DJet help bucking, stuttering

[akokarski]

Hi Guys,

Per Ray's suggestion posting here for help with T3. He's convinced me to keep at it, so I am giving it another go.

Here is what is happening with the car. It starts ok, no pedal need it to get started and first minute of driving is ok. But as soon as I get out of the parking lot I get this bucking, or stuttering on small acceleration and cruising. I doesn't really matter what gear I am in. Can be happening on freeway in 4th. Feels like somebody is jerking on the car and pulls it back. I am guessing missfire one or more cylinders. Also doesn't seem like it's getting full power. This is not consistent, but gotten progressively worse. It's done it 1st day I picked it up when we bought it. Just a few pops nothing major. Now it's at the point were you have to accelerate and decelerate in order to minimize this jerking.

Now this been going on for about a year just gotten worse and worse. Here is a list of all the things that have been done so far to remedy these particular issues.

1) fuel pump was going out, got it replaced with e2000, fuel pressure was double checked and left at 28 or 26lbs. I will have to double check as I think I did dial it down to 26lbs.
2) Generator rebuilt, with t1 armature (1st rebuild didn't last too long)
3) solid state regulator was also replaced at the time
4) ground strap to tranny was replaced.
5) new injector seals
6) intake manifold gaskets (phenolic spacers are in place)
7) intake runner boots, replaced, old ones were brittle and fell apart when I replaced gaskets
new ignition parts (coil, cap, condenser, points, rotor and plug wires, plugs)
coil was leaking, cap was crap had cracks and was arcing to distributor body, few cracks in wires.
9) new hoses, to MPS, and from cleaner to aar to throttle box
10) MPS was replaced, didn't hold vac. I have it in my hands and waiting for vac tester to double check myself
11) a few tvs units were tried, no changed.
12) #3 injector connector was replaced.
13) I did ran tests with bosch tester everything seemed to be more less in spec, and no smoking guns were found.

Obviously dwell, timing and valves were rechecked, #3 exhaust seems to tighten up fairly quickly, so I've been leaving it a bit looser .008. Vacuum leak tests didn't show anything either.

Also checked trigger points resistance and that was ok as well.

So what else can I look at? I am thinking I can go over the basics and checking tvs adjustment per this http://www.shoptalkforums.com/viewtopic ... 2&t=102000

Thanks,
Anton

[Piledriver]

CHT resistor reads how many ohm cold and also check hot.
(frequently flakey item, perhaps the most likely other than a wiring issue)
Try replacing it with a 5K potentiometer.

Shoot for 28-30 PSI.

[raygreenwood]

Welcome! akokarski

What Piledriver suggested is a good starting place. One thing to know about D-jet is that it is 100% vacuum and resistance controlled. When one part...actually virtually any part..... is out of whack....it causes changes to the vacuum signature. That vacuum signature changes how the engine is enriched....which in turn changes the vacuum signature further.

Typically the bucking is largely caused by a variation in baseline fuel mixture...either rich or lean. This makes the engine overly sensitive to small changes in acceleration enrichment.

Some things to check:

(1) as piledriver noted. We need to know your CHT reading cold and then fully warmed up.
(2) I need to know how the ignition is timed and also what your timing is reading at idle (what is your idle rpm). Is the timing jumping around when you have the light on it?
(3) have you checked your vacuum advance can for leaks? At a later point we will get to cleaning up slop in the distributor breaker plates and springs.
(4) What is your fuel pressure? What is it at idle? is it steady? if not..what level of fluctuation? Does it fluctuate wildly when you rev it?
(5) Have you adjusted your valves and how closely? D-jet is VERY sensitive to proper valve adjustment.
(6) what is the resistance reading of each side or your set of trigger points?

Now...this is usually a combination of things....but the TVS is usually a major part. Tell us exactly how it was adjusted and what the part # is...and which book you referred to when you adjusted it.
lets start there.
Ray

[akokarski]

Good morning!

Here is a list of things I can answer at the moment. I will get to check things on the car hopefully later tonight.

CHT was checked a while ago, it's one of the things that I forgot to list in the first post, I will double check it anyway it doesn't take long and who knows maybe a connection or sensor itself is acting up.

I am looking for something around 600ohms hot and 15k cold?

TVS wise I have 3, 2 newer style 0 280 120 040 and one older style (0 280 120 005). Currently newer is on the car and original is in my hands. It is adjusted per manual "turn counterclockwise till click + 2*"


Original infront and newer in the back.

Thanks,
Anton

[zooty]

Good morning!

Here is a list of things I can answer at the moment. I will get to check things on the car hopefully later tonight.

The D-Jet Points can cause this and not least the MAP.

Using an WBO2 can help to find the fault.

I think the Type-3 D-Jet don't have the acceleration enrichment so no pulses if the TPS is used.

Make sure your Valve clearance don't change much if the Engine is getting hot.

[raygreenwood]

Good morning!

Here is a list of things I can answer at the moment. I will get to check things on the car hopefully later tonight.

The D-Jet Points can cause this and not least the MAP.

Using an WBO2 can help to find the fault.

I think the Type-3 D-Jet don't have the acceleration enrichment so no pulses if the TPS is used.

Make sure your Valve clearance don't change much if the Engine is getting hot.

Yes...the D-jet type 3...all type 3...used TPS pulses...when they have the multi pin (4 or 5) TPS. I was going to wait to get into the trigger points because they warrant a page on their own. But since zooty mentioned it...here goes.

The trigger points can only cause this problem for one of several reasons (a) If the three pin plug has any connectivity issues at all. But...bear in mind ...tou noted that it was at very small throttle openings. If it were connectivity at the trigger point plug (which is a common problem)...it would happen all across the rpm range. (b) the center wire of the three..the ground...is not grouning properly. Typcially it is grounded to two areas....one pin on TPS and one pin to the block. This is one of the most obscure tracings of the stock wiring diagram. (c) if the resistance is very high or imbalanced on either trigger set...it can cause poor or incorrect injection duration.

The trigger points should be no more than 1.2 ohms MAXIMUM for each trigger point as measured between center pin with the black probe and each side pin with the red probe.
More importantly....ideally...they should be lower resistance. You will be hard pressed to find a set even new whose triggers read below .5 ohms. each. If you do...suspect that your ohmeter is set in too high a range or is not a true 1 ohm meter and /or needs to be calibrated.
But...most improtantly...the difference between each trigger set in a pair....should not be more than .2 ohms.
Examples of what is good and bad:

1.2ohms and 1.2 ohms......good but at the extreme high end of resistance
1.2 and .9 ohms.....bad because the resistance is greater than .2 ohms difference from side to side.
.8 or .9 ohms and .8 or .9 ohms.....good and about average
.5 ohms and .7 ohms....good...decently low...but at the extreme of allowable difference.

Much of this can be cleaned up. Remove the points. Clean with circuiit cleaner and dry well. Then draw a piece of paper from a brown paper bag or construction paper through the points to simply polish. DO NOT USE sand paper...unless it is 2000 grit or better. We are polishing them ONLY. There is no carbon on these like ignition points.

Also zooty makes a good point. Its what I consider pretty advanced tuning. But I set my valves to .006 cold like factory. Then warm teh car up until it is as hot as it can get...and check them when hot. Typically they close up about .003". If you find any that are way off...correct them then warm up and check it again to make sure it wasnt a measuring error. This is down the line tuning. For now...just good valve adjustment will do. It MUST be accurate. Do not get sloppy on valves.

The MAP in this car...is the MPS. Do not touch it for the moment except for one thing....is there a fat aluminum plug in the back with a flatblade screwdriver slot....about 1/2" in diameter?

If its a late model there should be be. DO NOT remove it. It is not a plug....it is an actual adjustment. If the plug is gone....you have found your problem.
A good start to teh adjustment for this ....is....and this is ONLY when the engine is idling......at correct idle...screw the plug in until it just grazes the copper plate within. If you go even a 1/10th of a turn too far the car will try to stall. Then...back it out about 3/4 turn. Mark it with a sharpy marker. Drive it and see if its lean and popping off the line wit ha flat spot. If it is...turn it out 1/8th turn at a time until it stops.

Do NOT do anything else to the MPS at this time. All else must be done and correct before you start with it.

What is your outside temperature?
The CHT should start out around 1800-2000 ohms in say...75-80F weather on a cold engine. Maybe a little less. But it shoudl end up fully wramed up at about 125-250 ohms. It can in hot weather drop all the way to 70 ohms.

We will get into the TVS....later in detail. But most of the books are very incomplete. In reality you must hold the throttle plate closed. Cycle theswithc all the way closed. Observe the forked floating switch being on the rearward pole. With voltmeter on continuity...move until you hear beep or see needle swing....AND...AND also observe that the forked switch is forward contacting the forward round brass pole.
Lock one screw. Now...cycle the throttle plate through full arc and let the spring return it to full closed.
With a magnifying glass an light verify that the at rest position for the wiper contact is right at the edge....within about .003"...of making contact with one of the lines of the enrichment grid...or already making contact.....AND verify that in this closed position the forked floating switch is making contact with the rearward round brass pole....which is off.

Now..slowly open the throttle plate....observe that before the wiper contact moves off of the contact strip that it is either entering or sitting on....that the forked switch has moved forward and made contact with the round forward pole or pin...which is on.
IF....IF....the wiper contact moves off of the first metal contact strip on the circuit board BEFORE the forked switch makes contact on the forward pin....it means that you have more than 2* of slop in teh switch (very common...and very correctable...on late switches)........this alone will cause the bucking syndrome. Ray

[akokarski]

I am back. Wasn't able to check everything, just too late and dark, but I wanted to check at least what can in the mean while.

CHT Cold came up with 3620-3650 ohms it is about 62* outside according to weather channel...
Ran a car for a few minutes just idling, so no load and it is nowhere normal operating temp measured it again and was just under 300ohms. I watched it go from 295ohms to 300ohms with in a min.

Checked trigger points, i didn't remove them from distributor just yet so I don't disturb the timing. One side came up with .4 and other at .3ohm. I did try my multimeter before hand with a set of trigger points on my desk those came out to 1.0 and .4.

Also I did polish my set in the past with brown paper.

The rest will have to wait till the weekend, 3 more days

Thanks,
Anton

[zooty]

The MAP in this car...is the MPS. Do not touch it for the moment except for one thing....is there a fat aluminum plug in the back with a flatblade screwdriver slot....about 1/2" in diameter?

If its a late model there should be be. DO NOT remove it. It is not a plug....it is an actual adjustment. If the plug is gone....you have found your problem.

Yeah! Very good Post Ray.

"First" Type-3 (Germany 68) have had the sort version of the MAP (MPS) so it as always important to know what the used D-Jet have in real.
Yes, the Kangaroo-Effect is mostly the TPS alignment or or an Air-Leak.
If this D-Jet-Computer have an Co2 POT this can also influences this Kangaroo-Effect. (too lean)

[akokarski]

Quick question about vacuum leak test on mps and distributor advance can. What should I pump it too and how long should it take to leak? Or it should not leak no matter what.

Thanks,
Anton

[raygreenwood]

About the maximum you should expect in vacuum is about 18" hg....about 15" hg is normal. Pump it to about 10-15. It should hold indefinately....but dropping a few inches over say...3-5 minutes....is not a big problem. Apply a littkle light oil around the seam and see if that stops it.

Also...what is the part # on your MPS....and does it have the large round slotted screw cover in the back.....or a cast-in plug of epoxy covering that large screw, or is is a small slotted screw or an allen wrench adjustment? A picture of the back end would also be nice. Ray

[akokarski]

original is out of the car, it was swapped as it was not holding vac. Original has a rounded slot screw (out of the car). The one in the car is expoxied. I will get part #s.

Is there a spec in one of the manuals to what resistance I should be getting from MPS at certain vac?

Thanks,
Again

[Lars S]

The resistance in the MPS is fixed (only changes a bit due to temperature, not by pressure). The feedback used when pressure changes is a change in inductance, this can be measured with an inductance meter which will show the inductance in Henry.

There is a lot that can be told about the MPS, Paul B. Anders has already written most of it, thanks again Paul!
Please se this link:
http://members.rennlist.com/pbanders/ma ... sensor.htm


/Lars S

[zooty]

Quick question about vacuum leak test on mps and distributor advance can. What should I pump it too and how long should it take to leak? Or it should not leak no matter what.

All Air-Leaks make trouble.
At part load the Injector sealing can become an leak. I have seen the are new but how knows.
Sometimes the Housing of sensors can suck air also the Cold start valve seal if you have one.

Dump Questions;
Is it possible to put this old distributor 180° wrong in place, or the D-Jet trigger Connectors?
Have you changed the placing of the MAP (MPS)?

[raygreenwood]

Zooty, it is possible to put the distributor in 180* out. It will be an odd fit with the vaccum can....but its possible. Its also possible to have a type 4 distributor for D-jet in a type 3 car...and have it run very strangely. So its probably a good idea to post the distrubutor part # just in case.
If the distributor is in 180* out...the trigger points will be as well...though that will be less of a running problem than the ignition timing issue.

With the distributor in correctly...it is not possible to install the D-jet points 180* out of time.....but this is a good point you make. So it is not a dumb question.
You CAN have the injector plugs plugged into the wrong injectors....and that WILL make the injection timing 180* out of time and will cause running issues.

So make suure that they are plugged in with the black boots toward the back of the car...on #'s 2 and #4...and the white/gray boots go toward the front of the car on #1 and #3.

The reading on the CHT is a bit high. Can you tell us what the part # is on your ECU and what the part # is on the CHT? Ray

[zooty]

You CAN have the injector plugs plugged into the wrong injectors....and that WILL make the injection timing 180* out of time and will cause running issues.

I have some winter's Day plugged in the D-Jet three pin connector on the distributor 180° wrong and that makes the same problem.
So control it!