Yep, VW, Porsche, Mercedes, Renault....and a couple of others...used D-jet.
Ok. About adjusting the MPS. It will help greatly to read Brad Anders D-jet website. I think Brad is an electrical engineer. He has teh most comphrehensive research on what was in the system, how it works and why it works and a vast range of test data.
On a few points here and there...mostly performance and operation related, I disagree with some of his conclusions. But not his research. He is 100% spot on about what the electronic limitations and internal sequencing of the system are.
That being said, the system is NOT just the sum of its electrical limitations. There is vacuum involved, cam dynamics, fuel pressure stability, temperature fluctuations...and the ability to "lie" to the system to augment the data it gathers. While this will not ever get the ECU to do things that are not within its electronic limitations....it can greatly change the way fuel is delivered...at different times and temperatures. With fuel injection...timing and temperature is everything.
For instance....in the past, there have been conversations regarding the fact that the stock PCV valve and the way it operates has no real bearing on the system. I have found through direct tracking and a jillion miles of tuning and driving...that this is NOT true. It has a great affect. Also....although Brad is 100% spot on about the range of electrical effectiveness of responses within the ECU...to what parts like the MPS, CHT and ambient air temp sensor send to the ECU, there is a lot of tuning that can be done...that is not within factory literature. Just because they did not do certain things to take advantage of the way a given engine responds...does not mean that it can not be done. The last thing that I have ranted long about...is that fuel pressure stability is KEY...in any vehicle with a fixed fuel pressure. It must be spot on...rock solid...unwavering. Because...the system is assuming the pressure is at a fixed point and is making all of its decisions accordingly...and has no downstream sensors like 02 to tell it otherwise.
That much being said....some of the things I will tell you to do to the MPS...may go slightly against the grain of what others say. I will have to finish this post in a few..I'm at work.
Ok...to start adjusting...first you must look at a cutaway of teh MPS to understand what all the parts are. This will be adjusting...without the benefit of a wavetech unit for baselineing work. This also assumes that you have an MPS that has not been "fiddled" with. In other words...it ran good...but needs a tweek or two. This is for stock engines, stock engines with say...a better exhaust and ignition, stock engines withj a webcam 73.....or a near stock engine with all of these improvements...like webcam 73, slightly better exhaust, better ignition and slightly larger valves. In other words....the MPS basically at factory adjustment...runs decent...but is a little lacking here and there.
This will be assuming....no vacuum leaks, properly adjusted valves, stable fuel pressure , proper timing....after valve adjustment, good harness, no electronic issues, proper charging and good battery, clean ground connections, properly adjusted TPS, and all senors reading factory specs at cold and hot settings and at least properly operating PCV valve.
The basic layout of the MPS..from back to front (front is the end with the vacuum line) ...goes like this:
(1) Tamper proof plug with expoxy filler on outside. This plug is not just a plug. It is teh outer enrichment diaphram stop screw. When you remove the epoxy....make dang sure that you do not move this screw plug...yet.
(2) Under that plug...is visible the copper full load enrichment diaphram.
(3) In teh center of that diaphram...is a screw that takes a flat blade screwdriver. That is your main fuel mixture adjusting screw. In is rich...out is lean.
(4) SURROUNDING that flat blade adjustingscrew...is a ring....that appears to have what looks like teh shape of a hex bolt or but...machined into it. This is also an adjusting screw. It requires a "hollow" hex key to adjust that screw...while holding teh center flat blade mixturescrew still...with a screwdriver. That is the inner stop adjustment screw for the full load enrichment (copper) diaphram. It will beexceedingly rare that this adjustment needs to be moved. It sets the stroke "in-stroke" depth for the diaphram. If its set to go too far...you get too much enrichment...or can go so far as to exceed the range of useful measurement of the ECU and cause stalling. It can also cause the stroke to be so long on the diaphram that it causes unecessary fatigue and cracking.
(5) Key-hole stop plate. This is the inner plate that the inner stop screw for the diaphram bears against.
(6) Barometric aneroids. These are factory specified chambers that react to the atmosphere surrounding them by expanding or contracting. Under full vacuum at idle...they are fulling expanded...causing the iron rod (armature) to push further into the magnetic coil (lean). On opening the throttle and releasing vacuum...the aneroid chambers contract...moving the rod out of teh coil (enrichment)
(7) Armature rod....described above. It is suspended in two axis by axial coil spring in the back (whcih is the factory calibrated laod spring), and leaf springs laterally...front and rear....to suspend it centrally between ceramic guide bearings.
Thats the list of parts in play. Heres what happens: Upon adding vacuum (throttle closed) the twin barometric chambers expand. The rod pushes into the coil...leaning you out to maximum lean. At thissame time...the copper plate is vacuumed inward onto its stop...which is the keyhole plate. When you open the throttle.....atmospheric pressure rushes in....that "squashes" the twin aneroid barometric chambers....very rapidly. This moves the rod out very quickly from teh coil....causing a rise in pulsewidth in teh ECU to the injectors....it gets richer. Sowhat does the copper plate do at this moment? Its is actually slightly quicker than the barometric chambers. It flexes outward rapidly...releasing some of the tension on the barometric chambers...allowing the spring pressure on the rod to flex the barometric chambers inward at an even faster RATE. But...since it is more flexible (the copper plate)...it takes very little vacuum to pull it back in...plus it has spring force in it. So...it is an immediate extra enrichment blip..but returns some tension to teh chambers almost immediately. It allows a faster rate of movement on the aneroid chambers. It also has outside barometric pressure acting on it...so it is a slight rate limiter to the contraction....and re-expansion of the barometric chambers...according to the outside weather. It Is stopped from over flexing...and over-enriching...by that outside aluminum plug.
So...all in all...there are three main adjustments available to the MPS. more later....Ray
Not a single good MPS in the whole lot...
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
So...in general. If all is generally good with the engine and fuel injection system....all you should be adjusting.....is the main load adjuster screw with teh flat blade screwdriver in the middle of the copper plate.
Make sure you mark your starting position with a FINEPOINT sharpy. I also mark the surrounding screw ring (the innerstop adjustment to make sure that this is not turning while I make the mainload screw adjustment (flat blade screw).
To start off. DO REMOVE THE OUTER ALUMINUM PLUG....YET...unless the engine is idleing under vacuum. DO NOT EVER SCREW IN THE ALUMINUM OUTER STOP PLUG unless the engine is either under vacuum at idle...or you know the exact number of turns to move.
Mark the plug in the back with a sharpy. With the engine warmed up and idleing.....AND with the gray mixture knob on the ECU (if you have one) set in teh middle (11-12 clicks)......count the number of whole and partial turns it takes to remove the aluminum plug. Write it on the MPS with sharpy...and also on paper.
You can now see the adjuster screw. NOTE: if you rev the engine with the aluminum plug REMOVED...it will have arich flat spot...because the copper full load enrichment diaphram will be un-retsrained...and travel out to far.
If your engine is running rich slightly .....turn the center screw about 1/6 turn...counter clockwise. If it is slighlty lean....adjust the center screw 1/6 turn clockwise.
At this point...I recommend going to teh workbench to drill a 3/16" hole in teh center of the aluminum plug to get a small screwdriver through it....so you can re-install it to teh correct number of turns/depth...and then be able to rev the engine after each adjustment looking for overly rich flat spots.
After each adjustment....rev it a ocuple of times...re-set the idle...and drive it.
Drive it on a set course with some stop signs and ups and downs. Make sure the outside weather is...average. Get a pen and paper...and make notes...as to wether there are flats spots off teh line...or after gear shift or week spots...or stumbling when accelerating from say 45 mph or higher cruising speed....by pushing the pedal down about 2/3 way.
Yes...if you are very encremental...and take pains to let the car cool down when hot...and this is best if you have a CHT gauge.....then it can be almost dialed in like a carbuettor.
In moderate weather (like fall or spring)..when the ambient temp is between say 68-80 F....i sometimes tune by disconnecting the wiring harnes from teh CHT..and putting in a 125 ohm resistor...so as not to "taint" the tuning tweeks by maxing out the CHT. Minor temp flucuations will not affect the tune too much....but they do affect the CHT alot. It canquickly reach its max low OHMS...which is generally to low...and not recover due to heat banking anjd the inability to shed the heat.
If all ranges are excellent....but you keep getting a flat spot off the line, try to ascertain wether it is a rich flat spot...or a lean flat spot. If it is rich...(but only right off the line)....you can turn the outer stop aluminum screw in about 1/5 to 1/3 turn. It slightly reduces the amount of extra enrichment that the full load copper diaphram plate gives. If its too lean...go 1/5-1/3 turn counterclockwise (out). This will allow a slight amount more enrichment but only off the line. More later. Ray
Make sure you mark your starting position with a FINEPOINT sharpy. I also mark the surrounding screw ring (the innerstop adjustment to make sure that this is not turning while I make the mainload screw adjustment (flat blade screw).
To start off. DO REMOVE THE OUTER ALUMINUM PLUG....YET...unless the engine is idleing under vacuum. DO NOT EVER SCREW IN THE ALUMINUM OUTER STOP PLUG unless the engine is either under vacuum at idle...or you know the exact number of turns to move.
Mark the plug in the back with a sharpy. With the engine warmed up and idleing.....AND with the gray mixture knob on the ECU (if you have one) set in teh middle (11-12 clicks)......count the number of whole and partial turns it takes to remove the aluminum plug. Write it on the MPS with sharpy...and also on paper.
You can now see the adjuster screw. NOTE: if you rev the engine with the aluminum plug REMOVED...it will have arich flat spot...because the copper full load enrichment diaphram will be un-retsrained...and travel out to far.
If your engine is running rich slightly .....turn the center screw about 1/6 turn...counter clockwise. If it is slighlty lean....adjust the center screw 1/6 turn clockwise.
At this point...I recommend going to teh workbench to drill a 3/16" hole in teh center of the aluminum plug to get a small screwdriver through it....so you can re-install it to teh correct number of turns/depth...and then be able to rev the engine after each adjustment looking for overly rich flat spots.
After each adjustment....rev it a ocuple of times...re-set the idle...and drive it.
Drive it on a set course with some stop signs and ups and downs. Make sure the outside weather is...average. Get a pen and paper...and make notes...as to wether there are flats spots off teh line...or after gear shift or week spots...or stumbling when accelerating from say 45 mph or higher cruising speed....by pushing the pedal down about 2/3 way.
Yes...if you are very encremental...and take pains to let the car cool down when hot...and this is best if you have a CHT gauge.....then it can be almost dialed in like a carbuettor.
In moderate weather (like fall or spring)..when the ambient temp is between say 68-80 F....i sometimes tune by disconnecting the wiring harnes from teh CHT..and putting in a 125 ohm resistor...so as not to "taint" the tuning tweeks by maxing out the CHT. Minor temp flucuations will not affect the tune too much....but they do affect the CHT alot. It canquickly reach its max low OHMS...which is generally to low...and not recover due to heat banking anjd the inability to shed the heat.
If all ranges are excellent....but you keep getting a flat spot off the line, try to ascertain wether it is a rich flat spot...or a lean flat spot. If it is rich...(but only right off the line)....you can turn the outer stop aluminum screw in about 1/5 to 1/3 turn. It slightly reduces the amount of extra enrichment that the full load copper diaphram plate gives. If its too lean...go 1/5-1/3 turn counterclockwise (out). This will allow a slight amount more enrichment but only off the line. More later. Ray
-
ubercrap
- Posts: 1394
- Joined: Sun Apr 18, 2004 8:00 pm
So, given that the chances of getting a correct, new MPS are slim, should one buy any new one they can get (Volvo, Mercedes,etc.), if they are available then- adjust it to work as you are outlining? It seems like there is a good chance that even a good original used one will fail sometime soon, given that there are so many bad ones out there now.
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Yes. There are some minor differences. In all that I have opened ..between VW, Porsche and I think a few volvos...there is little difference if any...between the aneroid chambers. Brad anders may be able to tell you if there was any actual difference in the factory atmospheric pressures in the chambers or not.
In my book.....itwould make little difference if there was. It is...just a barometric spring. Thats all. If that barometric spring is just a little different...then adjust around it.
Some differences that are different.....there is what I call a "long horn" and "short horn" version of the MPS. I have seen both long and short...across all vehicles. Some are differnt in part number...some are the same. I have "E" series MPS's from 412 with both long and short horns.
That refers to the length of the case around teh main spring as it protrudes from the MPS body...by the vacuum nipple. There are minor response differences between teh two. Both will work on the same engine equally well..when adjusted for it. Once my beast is back on teh road....I will delve into mapping teh differences.
Late model D-jet stuff....like 73 to 75...I started noticing that the MPS's...were coming with paint mark grading. The adjustments are differnt on those.
It has long been my contention...for many good reasons....that in teh early days of both type 3 non-diaphram MPS and into the first year or so of diaphram type.....the MPS adjusting as it came from teh factory....was just kind of generalized. All the cars ran good....but no MPS seemed to be exactly 100% dialed in for theengine it came with. As engines started to get wear in them...and lose efficiency.....the delaer would swap in a new MPS with the same original factory baseline...and it would do no good.
The dealers NEVER adjusted the MPS's on site. They just put in new parts.
I found a great many 411/412 in great shape....that could not be made to run well...and wer deemed lemons by teh owners...and ended up sitting behind some repair shops shed for a long time. I speculate...that in the later years...when the paint marked versions started arriving....they had different grades of tune.
A couple years ago when Brad Anders first started talking about baselineing an MpS on teh bench with a wavetech meter...and setting to factory baselines...I had a few objections. Yes...its the best way to start so the car will run...so you can tune it. A while back there were a couple of people (I think Jeff Bowlsby was one) that were baselining MPS's for people through the mail. I have had a few e-mails from people upset...because their newly baselined MPS...did not run well out of the box.
Well ...of course it wouldn't run perfectly with just a baseline factory setting. Is your engine still factory fresh?....and even then....are the characteristcis exact for the baseline set?....and do you have any mechanical mods done at all? ie:..better cam, port work, bigger valves, better exhaust, higher or lower compression, different distributor, sloppy distributor, different harness, different ECU....the list could go on for a page.
Each MPS.....I have ever found...can almost ALWAYS be tuned to a higher state of tune than the facftory put on theirs.
If you put on a pertronix...its almost a given that your fuel mix will need a tweek. If you put on a better fuel pump and stabilize the fuel pressure....better the an the 2+ psi flux that teh factory had even when teh pump was new.....tuning the MPS...will open up a whole range of better driving. Ray
In my book.....itwould make little difference if there was. It is...just a barometric spring. Thats all. If that barometric spring is just a little different...then adjust around it.
Some differences that are different.....there is what I call a "long horn" and "short horn" version of the MPS. I have seen both long and short...across all vehicles. Some are differnt in part number...some are the same. I have "E" series MPS's from 412 with both long and short horns.
That refers to the length of the case around teh main spring as it protrudes from the MPS body...by the vacuum nipple. There are minor response differences between teh two. Both will work on the same engine equally well..when adjusted for it. Once my beast is back on teh road....I will delve into mapping teh differences.
Late model D-jet stuff....like 73 to 75...I started noticing that the MPS's...were coming with paint mark grading. The adjustments are differnt on those.
It has long been my contention...for many good reasons....that in teh early days of both type 3 non-diaphram MPS and into the first year or so of diaphram type.....the MPS adjusting as it came from teh factory....was just kind of generalized. All the cars ran good....but no MPS seemed to be exactly 100% dialed in for theengine it came with. As engines started to get wear in them...and lose efficiency.....the delaer would swap in a new MPS with the same original factory baseline...and it would do no good.
The dealers NEVER adjusted the MPS's on site. They just put in new parts.
I found a great many 411/412 in great shape....that could not be made to run well...and wer deemed lemons by teh owners...and ended up sitting behind some repair shops shed for a long time. I speculate...that in the later years...when the paint marked versions started arriving....they had different grades of tune.
A couple years ago when Brad Anders first started talking about baselineing an MpS on teh bench with a wavetech meter...and setting to factory baselines...I had a few objections. Yes...its the best way to start so the car will run...so you can tune it. A while back there were a couple of people (I think Jeff Bowlsby was one) that were baselining MPS's for people through the mail. I have had a few e-mails from people upset...because their newly baselined MPS...did not run well out of the box.
Well ...of course it wouldn't run perfectly with just a baseline factory setting. Is your engine still factory fresh?....and even then....are the characteristcis exact for the baseline set?....and do you have any mechanical mods done at all? ie:..better cam, port work, bigger valves, better exhaust, higher or lower compression, different distributor, sloppy distributor, different harness, different ECU....the list could go on for a page.
Each MPS.....I have ever found...can almost ALWAYS be tuned to a higher state of tune than the facftory put on theirs.
If you put on a pertronix...its almost a given that your fuel mix will need a tweek. If you put on a better fuel pump and stabilize the fuel pressure....better the an the 2+ psi flux that teh factory had even when teh pump was new.....tuning the MPS...will open up a whole range of better driving. Ray
-
vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
So can the output performance of the MPS be tested with a multimeter? So the MPS is vacuum driven; is the MPS just a vacuum switch or a dynamic vacuum switch? I mean is there only so many answers that the MPS gives to the ECU? Like on/off ,full on/off?.... Could you adjust the MPS by putting a adjustment type valve in the vacuum line or would that not work since there is a low vacuum setting and a max.? So does the ECU change based on a delivered resistance range of one of the source wires from the MPS, does that mean that a pourly adjusted MPS is out of the resistance range so it doesnt turn on the ecu switch? I was wondering if there was a plug type or jumper wire solution for the MPS source to ecu that could give you a tuning solution? Would be Nice to have a four wire plug you could make with adjustment screw for tuning!! Then you wouldnt have to chance damaging a working MPS..bill
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
The MPS...yes...technically runs on vacuum. That is to say, that the sealed chambers that are inside, react to vacuum by expanding and contracting. This moves teh rod or armature.
That rod....because of vacuum....moves in and out of a magnetic induction coil. Power is supplied to that coil....creating a magnetic field. That magnetic field is affected by the iron rod that moves in and out of it. The ECU....gets a reading oc the change in induction and uses that data just like info from the other sensors.
The MPS...is not just a switch. There are an infinite number of positions that the rod could move....in or out of the coil inside the MPS.
BUT.....the ECU can only operate between a certain minimum and maximum range of reading. It is easily possible to adjust the MPS...so the rod moves so far in or out...that it creates no more readable change within the ECU. So the range for minimum to maximum enrichment....is limited....but between those two limits....there are an infinite number of encrements. Wether the the ECU can create an infinite number of outputs...I don't know. I don't think it can....because its not that complex.
The meter used for tuning the MPS...when off the car and on a workbench....goes by several names. It is technically an inductance meter. Wavetech is a brand name. It actually feeds a set current through teh coil and reads the output. Of course you will need to operate the MPS with a hand vacuum pump and very very accurate gauge....to see what teh wave tech tells you when certain ranges of vacuum are applied.
This tool is used to baseline adjust an MPS that is totally unadjusted...and "unknown". From there...once the car is running....yes ...a dynamometer will be agreat way to adjust. But the best way to get best driving and smoothest running is either driving and adjusting...or driving on a chassis dynamometer.
The difficult part of tuning the MPS.....is somewhat within its design. You need a certain amount of spring pressure to keep the aneraoid chambers compressed....and to make teh whole armature stack move teh right amount...and at the right speed ....so you get good throttle response....and also...so the amount of distance the rod is driven in...or pulled out of teh armature....is directly proportional to teh amount of load selected by moving the gas pedal.
The problem with all of that...is that teh main spring pressure...whenset correctly.....can also be "snappy" enoough to very quickly return the armature to a position of less enrichment...when you still need some enrichment. This is seen when the car does not have enough part throttle enrichment. Meaning the throttle is partway open...vacuum is low...nearly at external atmospheric levels....you are not really accelerating...but are still adding some power. What happened....is that upon opening the throttle.....the swelled out vacuum aneroids...collapse quickly. The spring...driving the rod out of the coil.....has some rebound. So do teh support leafsprings...and so does teh copper plate. So teh rod moves very quickly out of teh coil and teh car enriches. But then...instead of just hanging there where it is (the rod)...is subsides some..even though teh throttle has not been closed yet. You can have a tendency...like on high speed over run...to run a hair lean.
This is why...best running takes a very careful adjustment of the center screw...and also why TB sizing...and vacuum control are critical on D-jet.
Most of teh early MPS....all seemed to have teh short horn spring. This meant that it was pretty highly loaded spring. I think teh later long spring models seemed to have a little more flexibility.Ray
That rod....because of vacuum....moves in and out of a magnetic induction coil. Power is supplied to that coil....creating a magnetic field. That magnetic field is affected by the iron rod that moves in and out of it. The ECU....gets a reading oc the change in induction and uses that data just like info from the other sensors.
The MPS...is not just a switch. There are an infinite number of positions that the rod could move....in or out of the coil inside the MPS.
BUT.....the ECU can only operate between a certain minimum and maximum range of reading. It is easily possible to adjust the MPS...so the rod moves so far in or out...that it creates no more readable change within the ECU. So the range for minimum to maximum enrichment....is limited....but between those two limits....there are an infinite number of encrements. Wether the the ECU can create an infinite number of outputs...I don't know. I don't think it can....because its not that complex.
The meter used for tuning the MPS...when off the car and on a workbench....goes by several names. It is technically an inductance meter. Wavetech is a brand name. It actually feeds a set current through teh coil and reads the output. Of course you will need to operate the MPS with a hand vacuum pump and very very accurate gauge....to see what teh wave tech tells you when certain ranges of vacuum are applied.
This tool is used to baseline adjust an MPS that is totally unadjusted...and "unknown". From there...once the car is running....yes ...a dynamometer will be agreat way to adjust. But the best way to get best driving and smoothest running is either driving and adjusting...or driving on a chassis dynamometer.
The difficult part of tuning the MPS.....is somewhat within its design. You need a certain amount of spring pressure to keep the aneraoid chambers compressed....and to make teh whole armature stack move teh right amount...and at the right speed ....so you get good throttle response....and also...so the amount of distance the rod is driven in...or pulled out of teh armature....is directly proportional to teh amount of load selected by moving the gas pedal.
The problem with all of that...is that teh main spring pressure...whenset correctly.....can also be "snappy" enoough to very quickly return the armature to a position of less enrichment...when you still need some enrichment. This is seen when the car does not have enough part throttle enrichment. Meaning the throttle is partway open...vacuum is low...nearly at external atmospheric levels....you are not really accelerating...but are still adding some power. What happened....is that upon opening the throttle.....the swelled out vacuum aneroids...collapse quickly. The spring...driving the rod out of the coil.....has some rebound. So do teh support leafsprings...and so does teh copper plate. So teh rod moves very quickly out of teh coil and teh car enriches. But then...instead of just hanging there where it is (the rod)...is subsides some..even though teh throttle has not been closed yet. You can have a tendency...like on high speed over run...to run a hair lean.
This is why...best running takes a very careful adjustment of the center screw...and also why TB sizing...and vacuum control are critical on D-jet.
Most of teh early MPS....all seemed to have teh short horn spring. This meant that it was pretty highly loaded spring. I think teh later long spring models seemed to have a little more flexibility.Ray
-
vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
Hey Longbeach, do you have a t3 mps?
Sorry to change the topic but Longbeach do you have a type 3 MPS? I have been looking for one for my brother's t3 70 wagen!! I thought it looks a little different then my t4 one!
Ray, so it's kinda like moving the curve of the MPS and the initial jump of the curve of the MPS when you adjust the MPS? So is the MPS data just a input variable that changes the injector pulse? So the movement of the coil rod is the curve range/slope of the data to the ecu? So if the MPS is out of adjustment or there is a vacuum leak then the coil rod/curve range/slope to the ecu is out of dynamic range for the engine? I can see why you cant have any vacuum leaks! It really is amazing that the MPS is the main conditional element in the djet system and wasnt setup for easier adjustment! The MPS is such a big element in the basic running it seems it would be hard to actually get to the point where you could make an adjustment to the MPS! I mean even if you have a functioning MPS doesnt mean you have a working output to the ecu??? bill
Ray, so it's kinda like moving the curve of the MPS and the initial jump of the curve of the MPS when you adjust the MPS? So is the MPS data just a input variable that changes the injector pulse? So the movement of the coil rod is the curve range/slope of the data to the ecu? So if the MPS is out of adjustment or there is a vacuum leak then the coil rod/curve range/slope to the ecu is out of dynamic range for the engine? I can see why you cant have any vacuum leaks! It really is amazing that the MPS is the main conditional element in the djet system and wasnt setup for easier adjustment! The MPS is such a big element in the basic running it seems it would be hard to actually get to the point where you could make an adjustment to the MPS! I mean even if you have a functioning MPS doesnt mean you have a working output to the ecu??? bill
-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Yes...you are getting it. In reality...D-jet is just about the simplest EFI system made. That is....that it is not very complex. But...it IS...quite "complicated". Do you understand that difference?
The MPS...is just a MAP (manifold absolute pressure sensor). But...it incorporates an etxra function with the full load diaphram (the copper part).
What makes it exceedingly complex....and I think also....a much better reaction part....is the actual mechanical method that it works by.
As someone noted in a conversation here a while back....the modern MAP sensor is much more accurate technically. That is true.....but a modern MAP does not react "dynamically"....in the same fashion. The push and pull of the MPS...mimicks or reacts to the change of the airflow and the vacuum dynamic as well as outside atmospheric changes. It is NOT just equivalent to the MAP sensor. The MPS.....by itself....would not make a very good absolut: vacuum/pressure sensor in a modern vehicle. Likewise....a modern MAP sensor does not do well as the sole source of load sensing.
In that...lies the complexity of the MPS sensor....and its problems with tuning.
In the late 60's and 70's.....finding an accurate inductance meter....affordably....would have been out of reach of 99.9% of all drivers. As the manuals note, adjusting the MPS would have been beyond the scope of the average very good mechanic in those days.
Add to that...the need for everything in the engine to be as perfect or uniform as possible to make sure that you were not adjusting the MPS to react to a problem that may be fixed or adjusted later.
Because D-jet has no downstream corrections like 02...and very few sensors otherwise.....if you adjust the MPS when you have any of the problems I am going to list....there is no capacity in the system for the ECU to self correct.
Problems that will mess up MPS adjustment:
(1) Vacuum leaks of any kind. A vacuum leak reads as a throttle opening increase.
(2) Dirty, worn or high resistance trigger points. High resistance on the triggers and worn cam follower points...can change the injection cycle start and finish point and/or delay the signal start and finish. That may cut short...injection duration in the upper rpm ranges.
(3) Low, incorrect or unstable fuel pressure. This was an original tuning fault from the factory in my opinion. The car can still run fine....but remember....your fuel pressure is factory designed to be 28 psi. Every 1 psi you are off...at any time...is 3.57% of your mixture. Think of it like this. If 28 psi=100% fuel pressure...then there are 3.57 percentage points to equal 100...per each of the 1 psi encrements in 28.
With brand new from the box fuel pumps...of which I have a couple, with a very good gauge (mine goes to 40 psi and reads in 1/2 psi encrements anjd is accurate to 1/2 psi with 1% total scale accuracy)....I found that even with new regulators and even back-stopped regulators...you can have a standard fluctuation in fuel pressure from off idle when you crack the throttle.....of an average of 1.0 to 2.0 psi. That is 3.57 to 7.14% variation
. Because you have no 02 sensor...how is the ECU supposed to know the pressure is not the exact 28 psi it thinks it is?
I think it may have been Brad or someone else who commented that of course the factory knew of this variation ...and that it must be within the range of tolerance the system was designed to run ok with, so that this variation was not an issue. Well...yeah...so do you want to just run OK? Because in my opinion...thats all these cars did run...was OK...with factory tuning. Some ran really nice...others just ran smoothly and OK.
With a second fuel pump and some simple and thoughtful tuning to the fuel system...you can reduce this tolerance in fuel pressure to a max change of about 1/2 psi across the board. The tighter you can hold the variances in fuel pressure....the tighter and more exact you can tune the MPS.
(4) Poor adjustment of ignition timing. The injection timing itself was poor for low rpm use due to out of time injections. Since injection timing is done in the distributor and is therefore tied directly to ignition timing and also cam position...and again there is no 02 downstream to correct...ignition timing must be spot on. Also, these engines burned a pretty lean mixture for their day. The maximum advance nust be controlled as tightly as possible.
(5) Poor valve adjustment. The D-jet was extremely sensitive to valve adjustment. The standard range of adjustment for a carbed engine is just not good enough for these. I think I read somewhere that every .001 of poor adjustment at the valves was equal to about 2-3 dgrees of valve open cam timing error. One of these days I need to calculate that out . Wether its true or not....errors or differences in valve lash are very noticable on tehse engines. There was not much lift in the stock cam. You already have injection timing issues with reference to valve opening points. Any excessive slack in the valve lash also affects the vacuum signature. All of these factors combined make a large difference.
You will also find that any excessive advance, valve lash slop....have a large affect on the vacuum signature. You may not own a gauge that is sensitive enough to see this. You may also not see these vacuum fluctuations while watching at idle..............BUT.........with a very sensitive fuel gauge.....you will see....a 2-5 psi radical swing/oscillation in fuel pressure at idle...when either the ignition timing is too advanced...or the valve adjustment is far off...or both combined. This is because the MPS is affected by the fluctuation even though you may not have the vacuum gauge to see the fluctations. The fuel pressure gauge is one of THE BEST tuning tools for D-jet. This is also why I adjust all my valves cold, then re-check and re-set them hot if necessary. They should be between .002" and .003" when they are about as hot as is practical. There should not be a great difference between them. Not more than .001-.0015".....especially if the valve adjustment is being done prior to MPS adjustment.
(6) Heat banking and range problems in the CHT and the ambient air temp sensor. The aluminum extender that someone shwoed a while back for the CHT...is a great idea. Like I noted, when tuning the MPS...I will either replace The CHT temporarily with a fixed resitor...or ballast the CHT with a variable resistor...to keep it in a sane (non-maxed out...non fluctuating ) range...so I can adjust the MPS without wild range flucations affecting my adjustments.
(7) Injector resistance, spray pattern, cleanliness. The injectors need to be as close as possible in balance.
(8) Wiring harness, ground points and voltage supply. I cannot stress this enough. Your harness must be good...with few if any patches...and the cleanest, tightest, lowest resistance connections possible. Any extra resistance in the wiring or connectors...is read by the ECU....as changes in the sensors. It is worth every penny in tuning...to go out and buy a 12 volt voltage stabilizer for the fuel injection supply. The system can absorb some fluctuation by design and still run well....but just like fuel supply...the tighter you can hold the voltage supply...the tighter and more exact you can tune the MPS.
Lastly.....PCV valve. The factory one is driven from the inside...by cylinder blowby pressure. It is driven from the downstream side as well...by vacuum from the engine. It has habit of popping open...any time the combination of case pressure and vacuum exceed the unseating pressure of the spring inside. Since there is no sensor link to tell the ECU that this is happening.......how do you keep the MPS from reading this quick momentary addition of atmosphere into the plenum...as a throttle movement?...especially since the PCV tube dumps in about 1/2 inch from the MPS vacuum line? You can't. That is why I make my PCV valve wide open and then install a constant 3mm drilled orifice in line. That way you get plenty of PCV.....but its at a constant rate with no fluctuations. this wide open version can be adjusted for in the MPS baseline settings. Others have noted that they see no real changes coming from tehir PCV. I counter that if your system is as highly tuned as it could be...and you have an accurate enough gauge...you will definately see negatives from PCV...and get noticable performance benfits from tuning them out.
So how did I ascertain that the PCV was actually giving problems? Simple. I replaced the 12mm tube that goes from the PCV to the plenum...with a clear piece of vinyl tubing temporarily. I had to put a coil spring in it to keep it from collapsing. I cleaned the living crap out of the PCV valve. I glued a 1/16" diameter red plastic tooth-pick to the plate/disc in the PCV with JB weld. It sticks up into the clear tube like a flag on the 18th hole of the golf course.
Start the car with your very accurate fuel gauge on...and watch the movement of the toothpick with the gauge right next to it so you can see them both together. You can also put the tachometer right next to this and see the movment. It can also be seen in with the dwell meter or timing strobe. Every time there was oscillation or movement of the red plastic pick....signaling opening of the PCV by combined pressure or vacuum....there was a corresponding dip in fuel pressure of about 1- 1.5 psi...as the MPS reacted to the disturbance in vacuum. Clamping off the PCV hose..stopped this dead (I already had two pumps so the pressure was rock solid stable otherwise).
These are some things to look at. Ray
The MPS...is just a MAP (manifold absolute pressure sensor). But...it incorporates an etxra function with the full load diaphram (the copper part).
What makes it exceedingly complex....and I think also....a much better reaction part....is the actual mechanical method that it works by.
As someone noted in a conversation here a while back....the modern MAP sensor is much more accurate technically. That is true.....but a modern MAP does not react "dynamically"....in the same fashion. The push and pull of the MPS...mimicks or reacts to the change of the airflow and the vacuum dynamic as well as outside atmospheric changes. It is NOT just equivalent to the MAP sensor. The MPS.....by itself....would not make a very good absolut: vacuum/pressure sensor in a modern vehicle. Likewise....a modern MAP sensor does not do well as the sole source of load sensing.
In that...lies the complexity of the MPS sensor....and its problems with tuning.
In the late 60's and 70's.....finding an accurate inductance meter....affordably....would have been out of reach of 99.9% of all drivers. As the manuals note, adjusting the MPS would have been beyond the scope of the average very good mechanic in those days.
Add to that...the need for everything in the engine to be as perfect or uniform as possible to make sure that you were not adjusting the MPS to react to a problem that may be fixed or adjusted later.
Because D-jet has no downstream corrections like 02...and very few sensors otherwise.....if you adjust the MPS when you have any of the problems I am going to list....there is no capacity in the system for the ECU to self correct.
Problems that will mess up MPS adjustment:
(1) Vacuum leaks of any kind. A vacuum leak reads as a throttle opening increase.
(2) Dirty, worn or high resistance trigger points. High resistance on the triggers and worn cam follower points...can change the injection cycle start and finish point and/or delay the signal start and finish. That may cut short...injection duration in the upper rpm ranges.
(3) Low, incorrect or unstable fuel pressure. This was an original tuning fault from the factory in my opinion. The car can still run fine....but remember....your fuel pressure is factory designed to be 28 psi. Every 1 psi you are off...at any time...is 3.57% of your mixture. Think of it like this. If 28 psi=100% fuel pressure...then there are 3.57 percentage points to equal 100...per each of the 1 psi encrements in 28.
With brand new from the box fuel pumps...of which I have a couple, with a very good gauge (mine goes to 40 psi and reads in 1/2 psi encrements anjd is accurate to 1/2 psi with 1% total scale accuracy)....I found that even with new regulators and even back-stopped regulators...you can have a standard fluctuation in fuel pressure from off idle when you crack the throttle.....of an average of 1.0 to 2.0 psi. That is 3.57 to 7.14% variation
. Because you have no 02 sensor...how is the ECU supposed to know the pressure is not the exact 28 psi it thinks it is?I think it may have been Brad or someone else who commented that of course the factory knew of this variation ...and that it must be within the range of tolerance the system was designed to run ok with, so that this variation was not an issue. Well...yeah...so do you want to just run OK? Because in my opinion...thats all these cars did run...was OK...with factory tuning. Some ran really nice...others just ran smoothly and OK.
With a second fuel pump and some simple and thoughtful tuning to the fuel system...you can reduce this tolerance in fuel pressure to a max change of about 1/2 psi across the board. The tighter you can hold the variances in fuel pressure....the tighter and more exact you can tune the MPS.
(4) Poor adjustment of ignition timing. The injection timing itself was poor for low rpm use due to out of time injections. Since injection timing is done in the distributor and is therefore tied directly to ignition timing and also cam position...and again there is no 02 downstream to correct...ignition timing must be spot on. Also, these engines burned a pretty lean mixture for their day. The maximum advance nust be controlled as tightly as possible.
(5) Poor valve adjustment. The D-jet was extremely sensitive to valve adjustment. The standard range of adjustment for a carbed engine is just not good enough for these. I think I read somewhere that every .001 of poor adjustment at the valves was equal to about 2-3 dgrees of valve open cam timing error. One of these days I need to calculate that out . Wether its true or not....errors or differences in valve lash are very noticable on tehse engines. There was not much lift in the stock cam. You already have injection timing issues with reference to valve opening points. Any excessive slack in the valve lash also affects the vacuum signature. All of these factors combined make a large difference.
You will also find that any excessive advance, valve lash slop....have a large affect on the vacuum signature. You may not own a gauge that is sensitive enough to see this. You may also not see these vacuum fluctuations while watching at idle..............BUT.........with a very sensitive fuel gauge.....you will see....a 2-5 psi radical swing/oscillation in fuel pressure at idle...when either the ignition timing is too advanced...or the valve adjustment is far off...or both combined. This is because the MPS is affected by the fluctuation even though you may not have the vacuum gauge to see the fluctations. The fuel pressure gauge is one of THE BEST tuning tools for D-jet. This is also why I adjust all my valves cold, then re-check and re-set them hot if necessary. They should be between .002" and .003" when they are about as hot as is practical. There should not be a great difference between them. Not more than .001-.0015".....especially if the valve adjustment is being done prior to MPS adjustment.
(6) Heat banking and range problems in the CHT and the ambient air temp sensor. The aluminum extender that someone shwoed a while back for the CHT...is a great idea. Like I noted, when tuning the MPS...I will either replace The CHT temporarily with a fixed resitor...or ballast the CHT with a variable resistor...to keep it in a sane (non-maxed out...non fluctuating ) range...so I can adjust the MPS without wild range flucations affecting my adjustments.
(7) Injector resistance, spray pattern, cleanliness. The injectors need to be as close as possible in balance.
(8) Wiring harness, ground points and voltage supply. I cannot stress this enough. Your harness must be good...with few if any patches...and the cleanest, tightest, lowest resistance connections possible. Any extra resistance in the wiring or connectors...is read by the ECU....as changes in the sensors. It is worth every penny in tuning...to go out and buy a 12 volt voltage stabilizer for the fuel injection supply. The system can absorb some fluctuation by design and still run well....but just like fuel supply...the tighter you can hold the voltage supply...the tighter and more exact you can tune the MPS.
Lastly.....PCV valve. The factory one is driven from the inside...by cylinder blowby pressure. It is driven from the downstream side as well...by vacuum from the engine. It has habit of popping open...any time the combination of case pressure and vacuum exceed the unseating pressure of the spring inside. Since there is no sensor link to tell the ECU that this is happening.......how do you keep the MPS from reading this quick momentary addition of atmosphere into the plenum...as a throttle movement?...especially since the PCV tube dumps in about 1/2 inch from the MPS vacuum line? You can't. That is why I make my PCV valve wide open and then install a constant 3mm drilled orifice in line. That way you get plenty of PCV.....but its at a constant rate with no fluctuations. this wide open version can be adjusted for in the MPS baseline settings. Others have noted that they see no real changes coming from tehir PCV. I counter that if your system is as highly tuned as it could be...and you have an accurate enough gauge...you will definately see negatives from PCV...and get noticable performance benfits from tuning them out.
So how did I ascertain that the PCV was actually giving problems? Simple. I replaced the 12mm tube that goes from the PCV to the plenum...with a clear piece of vinyl tubing temporarily. I had to put a coil spring in it to keep it from collapsing. I cleaned the living crap out of the PCV valve. I glued a 1/16" diameter red plastic tooth-pick to the plate/disc in the PCV with JB weld. It sticks up into the clear tube like a flag on the 18th hole of the golf course.
Start the car with your very accurate fuel gauge on...and watch the movement of the toothpick with the gauge right next to it so you can see them both together. You can also put the tachometer right next to this and see the movment. It can also be seen in with the dwell meter or timing strobe. Every time there was oscillation or movement of the red plastic pick....signaling opening of the PCV by combined pressure or vacuum....there was a corresponding dip in fuel pressure of about 1- 1.5 psi...as the MPS reacted to the disturbance in vacuum. Clamping off the PCV hose..stopped this dead (I already had two pumps so the pressure was rock solid stable otherwise).
These are some things to look at. Ray
-
Longbeach412
- Posts: 308
- Joined: Thu Aug 19, 2004 6:34 am
Yes I do, check out my earlier postings for the datails & P/Ns. Jees, I thought they were the same basic component. Mine is still available to whomever needs it. Just let me know.Sorry to change the topic but Longbeach do you have a type 3 MPS? I have been looking for one for my brother's t3 70 wagen!! I thought it looks a little different then my t4 one!
-
412jen
- Posts: 34
- Joined: Mon Oct 03, 2005 2:55 pm
I really appreciate all the thought and effort into all this information. It is all completely over my head. My car's insurance runs out on Thursday. I will be parking it and hunting for a good used MPS and installing that. My main goal is to get it to have better mileage and to pass Aircxare emissions testing. Without that, it is a paperweight. After much discussion with my partner, we've agreed that I should sell my car after that. At this point in our lives we cannot afford to have a car that requires this much time effort and money. I need a relaible daily driver that isn't costing me $400 in fuel a month. If anyone has any information about selling Type 4's I would appreciate it. If you could send it to me via a MP that would be best so there isn't much space taken up on the board.
-
vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
Great info Ray!!! Thanks!! Our car's have amazing engineer componants!
Longbeach, I would like to buy your T3 MPS for my brother's squareback djet! Let Me know what you want for it and I'll send out a money order!
412Jen, I think our 30 plus year old cars once maintained like any other daily driver is very reliable and I used to get 28 mpg on the highway and that is good even these days! Any car needs hoses replaced and tuneups and parts replaced as needed! It's hard to have any car and not be able to fix it yourself but todays cars can be more expensive because of the componants that make the driveability! Basically it always comes down to the maintance cost and when you want to pay that bill,lol, it's gonna get you sometime on any car and when you have to do it all at once it hurts more but then you have to remember that you get to start fresh and know what you are driving that's why I think a car loses so much value over time because that bill is coming due,lol!! My brother's wife's Honda tranny had the recall bearing winey sound which I caught just before her warranty was out but if I hadnt it would have cost them 3,500! I had to take it for a drive with the Honda mech to prove it was the tranny! I dont know how much you spent on her but the 412 is a great car and good performer for it's day even compared to some of todays car; like I was reading the est mpg of a 1.6 twin cam econo car and it was for some reason 20 city/28 hwy?? Sorry to ramble on but the cost of the repair to a 412 by a good mech. could have been saved in a few month that was lost in poor performance and you would have a daily driver?? If a MPS rebuild was 188$ and that is your issue you make that up fast spending 400 a month! Too bad you cant find a good VW guy up that way!! I know it's hard these days when you could buy a new car and have a monthly payment and get all the goodies and good mpg but we are those who love the last of the aircoolers and have VW in our blood I guess,lol, or just like a challange! Sorry it has been so frustating for you but you have joined the club to bring her 30 year old beauty back! You might have done better with a carbed version maybe or a Ljet setup...later models! Even when my Mom's friend had a 69 convert beetle restored she spent 12-14k but had a head turner and a great daily driver! I always get caught saving the cars and spending the now due maintance cost but get a car I know what I have and feel safe and by that point have some understanding of the car for trouble shooting and where the issues are to keep a eye on! I must admit I did always love that availibility of parts when I had a beetle or early van with the 1600 but they still had there issues too,lol! Just you paid it in smaller increment,lol! I hope you'll find her a good home or get to see the job through to enjoyment! bill
p.s.Even the Chevy blazers when they came out with the new fuel line connections had fire issues and that was off the lot the first year that change came out! All makes have production issues with vendors and design changes needed!
Longbeach, I would like to buy your T3 MPS for my brother's squareback djet! Let Me know what you want for it and I'll send out a money order!
412Jen, I think our 30 plus year old cars once maintained like any other daily driver is very reliable and I used to get 28 mpg on the highway and that is good even these days! Any car needs hoses replaced and tuneups and parts replaced as needed! It's hard to have any car and not be able to fix it yourself but todays cars can be more expensive because of the componants that make the driveability! Basically it always comes down to the maintance cost and when you want to pay that bill,lol, it's gonna get you sometime on any car and when you have to do it all at once it hurts more but then you have to remember that you get to start fresh and know what you are driving that's why I think a car loses so much value over time because that bill is coming due,lol!! My brother's wife's Honda tranny had the recall bearing winey sound which I caught just before her warranty was out but if I hadnt it would have cost them 3,500! I had to take it for a drive with the Honda mech to prove it was the tranny! I dont know how much you spent on her but the 412 is a great car and good performer for it's day even compared to some of todays car; like I was reading the est mpg of a 1.6 twin cam econo car and it was for some reason 20 city/28 hwy?? Sorry to ramble on but the cost of the repair to a 412 by a good mech. could have been saved in a few month that was lost in poor performance and you would have a daily driver?? If a MPS rebuild was 188$ and that is your issue you make that up fast spending 400 a month! Too bad you cant find a good VW guy up that way!! I know it's hard these days when you could buy a new car and have a monthly payment and get all the goodies and good mpg but we are those who love the last of the aircoolers and have VW in our blood I guess,lol, or just like a challange! Sorry it has been so frustating for you but you have joined the club to bring her 30 year old beauty back! You might have done better with a carbed version maybe or a Ljet setup...later models! Even when my Mom's friend had a 69 convert beetle restored she spent 12-14k but had a head turner and a great daily driver! I always get caught saving the cars and spending the now due maintance cost but get a car I know what I have and feel safe and by that point have some understanding of the car for trouble shooting and where the issues are to keep a eye on! I must admit I did always love that availibility of parts when I had a beetle or early van with the 1600 but they still had there issues too,lol! Just you paid it in smaller increment,lol! I hope you'll find her a good home or get to see the job through to enjoyment! bill
p.s.Even the Chevy blazers when they came out with the new fuel line connections had fire issues and that was off the lot the first year that change came out! All makes have production issues with vendors and design changes needed!
-
vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
-
Longbeach412
- Posts: 308
- Joined: Thu Aug 19, 2004 6:34 am
Hey Bill, here is a requote of my earlier posting regarding selling it :
So, once Ubercrap passes on it, I'll gladly send it to you.Hey, its not that big a deal, I got a couple laying around, been helped before by many members of this list, so am just passing on the deed. I'll try to get the P/N, if it matches yours, pay me the shipping (should be $5-$7) and when it gets there and it works, then you can pay me what I paid for it ( 20 bucks).
-
vwbill
- Posts: 970
- Joined: Sat Feb 15, 2003 12:01 am
Hey Uber, I tought you were looking for the 049 unit? My brother's T3 has the 007 or 051c in it. If you can use the 007/051c, I didnt want to jump in line!! It seems all us Djet 412 guys are looking for the 049 unit! LOL! Are you going to try the rebuilders? I'm thinking on that lines too since I only have a weird numbered one and one that leaks down slow in the car. I wont be getting to my re/rebuild till feb/march since I need to finish House siding on Mom's place before I do any car work! My brother's T3 is a nohold vacuum MPS,lol and a very leaky oil cooler or seal! It sounds like 412Jen needs a 049 first or she'll sell her baby or maybe that is already the case! What about you Uber, are you looking to get a driver now or setting up for the rebuild also? I dont think the MPS is something I could rebuild! I think it sounds like it is worth the price to have one done right! What you guys thinking? Longbeach if Uber doesnt want to try the 007/051c Email me your address and tell me want you want and I'll send it tomorrow! Thx bill
p.s.Believe me guys the only reason I sounded fast to jump on the 007/051c is because I got my brother his t3 wagen as a wedding gift and I am still after two years trying to get it running,lol!
p.s.Believe me guys the only reason I sounded fast to jump on the 007/051c is because I got my brother his t3 wagen as a wedding gift and I am still after two years trying to get it running,lol!