Okay, so I haven't had much time to play with the 412 this summer to figure out why she was only getting around 10MPG, and I finally decided to check the temp sensors (cyl head and air intake distributor).
For the CHT, I have 2330 ohms cold, and 96 ohms after a drive, and a few minutes idling in the driveway (this seemed to lower the resistance/raise temps).
For the intake distributor, I had 372 ohms cold, and 157 ohms after the drive/idling (this figure was the lowest I acheived by leaving the probes on after the engine was shut down, and the engine heat had a chance to rise to the intake).
Q #1: Are these within limits, or should I be looking for new sensors?
Q#2: Is the air intake sensor still an available part?
Q#3: Is there any place in particular to shop for correct replacement parts? (CIP1.com ?)
Thanks for any tips.
Travis
Temperature Sensors; Within limits???
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SureFit Travis
- Posts: 168
- Joined: Thu Mar 23, 2006 10:23 pm
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
All the sensors are still available...and bothe are between $30-35 US.
Technically...the CHT readings you are getting are within advertized limits. But....I have found it rare except in winter to get one that actually gets to 2300 ohms. Generally most of mine stay around 1900+ ohms. The 96 ohms is actually better than some. The sensor can go down to 70+ ohms as it heats up. This leans the fuel out......but it generally over-leans the fuel out. This makes most mechanics overcompensate.....and teh factory did as well....on the MPS settings. This gives too much fuel across the board.
Add to that.....the intake air temperature sensor. This device.....I think acorrding to Brad Anders research....adds somehere around 10-15% mixture change. Usually richer and across the range. It is poorly designed in my opinion and rarely has any useful encremental range because once the manifold gets hot...the sensor stays that way. I Generally disconnect the sensor and get MUCH better tuning and drivability in all months except teh very coldest...wherin I simply reach in and plug it back up.
Also....I found that ballasting the CHT to let it never drop below about 200 ohms makes for much better tunability and running. I also used at one time a variable cermaic resistor of from 200 to 2kohm....that I bought at Radio shack for $10....plugged into the air temp sensor to give it a settable but constant range. It worked very well in spring and fall....but in the coldest and hottest months...it required readjustment. Predictable yeah?
So...I went back to teh unplugged in all seasons except the coldest...and have no problems.
What really is the best for the sensor...and I will be doing on mine soon....is to have it plugged in for winter...and always......and have a thermotime switch that breaks the circuit when the engine reaches a certain state of wramed up.
That has generally been the pattern. In the coldest weather......plug it in and she starts on the first bump. Ten minutes later...as the AAR closes and she starts to idle down too low....unplug it...the idle stabilizes...and we motor away.
Also....poor grounds and high resistance connections....and minute vacuum leaks that increase as the engine warms up....cause low gas milage like you have. Ray
Technically...the CHT readings you are getting are within advertized limits. But....I have found it rare except in winter to get one that actually gets to 2300 ohms. Generally most of mine stay around 1900+ ohms. The 96 ohms is actually better than some. The sensor can go down to 70+ ohms as it heats up. This leans the fuel out......but it generally over-leans the fuel out. This makes most mechanics overcompensate.....and teh factory did as well....on the MPS settings. This gives too much fuel across the board.
Add to that.....the intake air temperature sensor. This device.....I think acorrding to Brad Anders research....adds somehere around 10-15% mixture change. Usually richer and across the range. It is poorly designed in my opinion and rarely has any useful encremental range because once the manifold gets hot...the sensor stays that way. I Generally disconnect the sensor and get MUCH better tuning and drivability in all months except teh very coldest...wherin I simply reach in and plug it back up.
Also....I found that ballasting the CHT to let it never drop below about 200 ohms makes for much better tunability and running. I also used at one time a variable cermaic resistor of from 200 to 2kohm....that I bought at Radio shack for $10....plugged into the air temp sensor to give it a settable but constant range. It worked very well in spring and fall....but in the coldest and hottest months...it required readjustment. Predictable yeah?
So...I went back to teh unplugged in all seasons except the coldest...and have no problems.
What really is the best for the sensor...and I will be doing on mine soon....is to have it plugged in for winter...and always......and have a thermotime switch that breaks the circuit when the engine reaches a certain state of wramed up.
That has generally been the pattern. In the coldest weather......plug it in and she starts on the first bump. Ten minutes later...as the AAR closes and she starts to idle down too low....unplug it...the idle stabilizes...and we motor away.
Also....poor grounds and high resistance connections....and minute vacuum leaks that increase as the engine warms up....cause low gas milage like you have. Ray
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SureFit Travis
- Posts: 168
- Joined: Thu Mar 23, 2006 10:23 pm
Hi Ray,
Yeah, I still have to replace the vacuum lines, but I noticed last night when checking the CHT that the nut on the closest intake manifold stud (to the CHT) was loose. Hmmm, vacuum leak perhaps?
I have new injector seals, new pushrod seals, new valve cover gaskets & intake gaskets........I just have to pick up some vacuum hose and get at 'er.
Thanks for the info on the sensors. I have a few booklets & manuals on the VW/Bosch F.I. (Elfrink, Harold T. Glenn's, an HP book on Bosch F.I., and a Bosch one which seems to be the vaguest of them all.....plus others....) as well as the usual Haynes and John Muir 'Idiot' book, but the best info I found within them were broad readings of 2500 cold and 60 hot for the CHT, and 500 cold to 100 hot for the intake. I felt it was better to ask the 'experienced community' for more realistic answers.
Again, thanks for repsonding.
Travis
Yeah, I still have to replace the vacuum lines, but I noticed last night when checking the CHT that the nut on the closest intake manifold stud (to the CHT) was loose. Hmmm, vacuum leak perhaps?
I have new injector seals, new pushrod seals, new valve cover gaskets & intake gaskets........I just have to pick up some vacuum hose and get at 'er.
Thanks for the info on the sensors. I have a few booklets & manuals on the VW/Bosch F.I. (Elfrink, Harold T. Glenn's, an HP book on Bosch F.I., and a Bosch one which seems to be the vaguest of them all.....plus others....) as well as the usual Haynes and John Muir 'Idiot' book, but the best info I found within them were broad readings of 2500 cold and 60 hot for the CHT, and 500 cold to 100 hot for the intake. I felt it was better to ask the 'experienced community' for more realistic answers.
Again, thanks for repsonding.
Travis
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
The Elfrink manual is very good....but bear in mind that 100% of all of the mnauals were written in the 70's. There was absolutely nothing any of these manuals could tell you.....that was not about JUST what factory set upo specs were on brand new systems. Thats brand new wiring, brand new parts.
As engines break in....parameters change. As engines get older, parameters change. As climates where cars are located are different from the factory...parameters change. Problem is....in none of these manuals is there any info on adjusting the actual fuel mixture at the MPS. Everything is just snap it together...check the hoses and wires, set timing, valves and TPS....and therefore it MUST run.
By the way...high resistance in connectors ....in general...in the wiring EFI harness can cause your milage problem also.
As you get these engines tuned out tighter an better....they run very well. But...the tighter they are tuned... the more susceptable they are to very small vacuum leaks. Be sure to check teh adjustment of the deceleration valve if you have one.
You will eventially get down to very minor leaks in things like throttle valve shafts. To combat that....I went to a 1.8 or 2.0 TB from a bus. A couple mm larger...and it has replaceable throttle shaft seals. It also fits the available o-ring. Use a tail pipe expander to widen teh spigot on the plenum about 2mm...and its straight bolt up and works well. Ray
As engines break in....parameters change. As engines get older, parameters change. As climates where cars are located are different from the factory...parameters change. Problem is....in none of these manuals is there any info on adjusting the actual fuel mixture at the MPS. Everything is just snap it together...check the hoses and wires, set timing, valves and TPS....and therefore it MUST run.
By the way...high resistance in connectors ....in general...in the wiring EFI harness can cause your milage problem also.
As you get these engines tuned out tighter an better....they run very well. But...the tighter they are tuned... the more susceptable they are to very small vacuum leaks. Be sure to check teh adjustment of the deceleration valve if you have one.
You will eventially get down to very minor leaks in things like throttle valve shafts. To combat that....I went to a 1.8 or 2.0 TB from a bus. A couple mm larger...and it has replaceable throttle shaft seals. It also fits the available o-ring. Use a tail pipe expander to widen teh spigot on the plenum about 2mm...and its straight bolt up and works well. Ray