Can anyone tell me which wires the TPS is connected to on the computer on my 94 Mark? I want to monitor the TPS voltage using an analog meter while driving to try to identify / find a intermittent problem. I know I can poke through the insulation near the TPS itself, but it would easier if I could ID the wires where they enter the computer. Any help is appreciated.
TPS Throttle position sensor wiring
- Thread starter ruswin
- Start date
I believe it's a green wire at the TPS
common sense would say it was the same colored wire at the PCM.
put your instrument on the TPS end of the loom and find the signal wire (the one that the voltage moves)
then go find that same wire at the PCM and verify....
it's not that terribly difficult if you think about it.
Not many times do wires change colors..
common sense would say it was the same colored wire at the PCM.
put your instrument on the TPS end of the loom and find the signal wire (the one that the voltage moves)
then go find that same wire at the PCM and verify....
it's not that terribly difficult if you think about it.
Not many times do wires change colors..
driller
Dedicated LVC Member
According to the '94 EVTM, at the PCM the TPS power wire is circuit 351/pin26 (BR/W) and the TPS signal wire is circuit 355/Pin17 (GY/W). The TPS ground is circuit 359 (GY/R) and grounds via splice S129.
OK, here's what I did. I removed the plastic cover from the computer connector to access the wires. I located the power wire, pin 26 (brown / white) and the signal wire, pin 17 (gray / white) and connected my analog multi-meter to it. I can now monitor the TPS signal while driving. It reads a little less than 1 volt dc when at idle up to just under 5 vdc when at WOT. Nice and smooth sweep as you increase the throttle position. I still have a bit of a high idle, it feels like the car is still pushing when coming to a stop, could the idle position or the calibration of the TPS be causing me the high idle? I will keep driving it like this until my funky transmission shifting problem resurfaces and then maybe I will catch the TPS giving a strange signal.
driller
Dedicated LVC Member
While the analog meter is nice to see the 'sweep', you really need a digital meter to calibrate the TPS. The TPS is factory calibrated and the screws are locked in with thread locker and are a huge PITA to loosen.
But as Tommy said, you want as close to .99VDC at idle as you can get without hitting 1.0VDC and you do not want the TPS to peg 5VDC at WOT. So, .99 to 4.99 is as good as it gets.
TPS not the problem with trans downshifting?
I checked the voltage from the TPS at the computer with a digital, and it is within the specs you quoted. I also drove it this weekend up to Phoenix and experienced the same intermittent problem with the car downshifting on it's own on the highway, and when it happens, a lot of time I can smell exhaust fumes backing up into the cabin. I have been chasing this problem now for a long, long time and would love to resolve it because the car is wonderful except for that problem, it only has 65K miles on it. Could it be some funky problem with the cats or something? Why would it drive fine for 1+ hours on the highway, and then randomly sometimes start downshifting from 4th to 3rd or even 2nd sometimes. The car will actually take itself out of OD over-ride on it's own when the problem occurs if I try to just run it home in 3rd w/o OD. I have now been monitoring the TPS sensor and it does NOT seem to be the culprit. My original post for the trans shifting problem is here. http://www.lincolnvscadillac.com/showthread.php?t=54247
I am also now suspecting either the computer itself, or maybe a faulty solenoid, wither the shift solenoids or maybe the TC lockup? I have removed the computer, inspected it and cleaned the connections, should I try another one? I installed this used trans from a 1998 Marquis to replace one that was completely toast, but this problem has not been resolved by the swap. The old 94 TC solenoid was re-used on the new 1998 trans when installed, is there any way to test the solenoids or monitor their function? I am trying to fight the good fight but damn!!!
I checked the voltage from the TPS at the computer with a digital, and it is within the specs you quoted. I also drove it this weekend up to Phoenix and experienced the same intermittent problem with the car downshifting on it's own on the highway, and when it happens, a lot of time I can smell exhaust fumes backing up into the cabin. I have been chasing this problem now for a long, long time and would love to resolve it because the car is wonderful except for that problem, it only has 65K miles on it. Could it be some funky problem with the cats or something? Why would it drive fine for 1+ hours on the highway, and then randomly sometimes start downshifting from 4th to 3rd or even 2nd sometimes. The car will actually take itself out of OD over-ride on it's own when the problem occurs if I try to just run it home in 3rd w/o OD. I have now been monitoring the TPS sensor and it does NOT seem to be the culprit. My original post for the trans shifting problem is here. http://www.lincolnvscadillac.com/showthread.php?t=54247
I am also now suspecting either the computer itself, or maybe a faulty solenoid, wither the shift solenoids or maybe the TC lockup? I have removed the computer, inspected it and cleaned the connections, should I try another one? I installed this used trans from a 1998 Marquis to replace one that was completely toast, but this problem has not been resolved by the swap. The old 94 TC solenoid was re-used on the new 1998 trans when installed, is there any way to test the solenoids or monitor their function? I am trying to fight the good fight but damn!!!
driller
Dedicated LVC Member
I installed this used trans from a 1998 Marquis to replace one that was completely toast, but this problem has not been resolved by the swap. The old 94 TC solenoid was re-used on the new 1998 trans when installed, is there any way to test the solenoids or monitor their function? I am trying to fight the good fight but damn!!!
Do you have the solenoids from the '98 tranny?
Have you checked the MLPS adjustment?
There is a test harness that can be used to test the solenoid operation but it's a needle in the haystack to find. Short of using a breakout box, I don't know what you could use to monitor the transmission solenoids.
FYI - the resistance for the shift solenoids are supposed to be between 20-30 ohms. The TCC solenoid resistance should be 1-3 ohms. The TOT sensor will be between 1K and 100K ohms depending upon temperature. You would need to disconnect the bulkhead harness or pull the solenoids to check their resistance.
Yes I think the MLPS is adjusted correctly, but I am unsure if it is still working OK. I replaced it once already, I have to assume it is OK.
Everything else you said makes sense,... What is a TOT sensor?
Everything else you said makes sense,... What is a TOT sensor?
Does the TOT sensor have any active role in the shifting schedule? I have installed an aftermarket cooler and the trans temp now stays below 180' all the time. Are the solenoids for the trans all 12 volt? In other words if I could figure out where the actual wires enter the PCM, and provide voltage directly to the solenoids bypassing the computer, I would be able to isolate the PCM and then it would have to be something in the trans wiring or a solenoid internally. Anybody have the ECM diagram that shows the connection to the trans solenoids? The other question is how would I get the TCC to lock up? Give it straight 12 volts?
No that solenoid os PPW, pulse width modulated.
putting 12V to it.. might work on the short term
But it's gonna SMOKE the solenoid in a very short time.
Some folks wired their TCC to lock up with a flip of a switch, and while it does work...it does cause other issues with failed parts.
to some extent, yes.. but I dont think it's the root of your issue here.
because there are also "timers" that tell the trans to exit the "cold shift strategy" as well at the TOT sensor.
So is there any other ideas to why the car will suddenly and randomly drop out of 4th, into 3rd or even 2nd at low speeds? The other symptom is the smell of exhaust and sometimes the AC clutch will be disabled... I am running out of things to look for.
as mentioned before that sounds like the common MLPS issue, but you've assumed the new part is both good and properly adjusted.
If your hell bent on a wiring issue, a common place to look is the trans harness where it runs next to and IMHO too close to the driver side exhaust.
Have you look at that stuff, since the issue has started?
I know you just put it in, and remember what it looks like..but.. ya might have to get under there and check things out.
you could swap another PCM into the car if you feel that might be the problem.
wish I could help more
If your hell bent on a wiring issue, a common place to look is the trans harness where it runs next to and IMHO too close to the driver side exhaust.
Have you look at that stuff, since the issue has started?
I know you just put it in, and remember what it looks like..but.. ya might have to get under there and check things out.
you could swap another PCM into the car if you feel that might be the problem.
wish I could help more
if you look at those two symptoms and ignore EVERYTHING ELSE.
that is a sign of WOT
car goes pig rich and the AC turns off.
then if you add in the trans downshifting, that's another sign of WOT or increased driver demand via the TPS.
MLPS causes some goofy downshifting stuff, but usually not accompanied by smelly exhaust and AC cycling off.
Only issue there is, you've check the TPS so much you probably know if it's prostate is in good health.
here is a thought, from the far side.
There is a lower dash panel that you've likely removed to get at the PCM wires, so when and if you can duplicate this issue.. reach under there, carefully and put your hand on the PCM. is it hot to the touch?
My 95 did some stupid shifting stuff once in a while and I thought it was a loose chip connection (DO YOU HAVE A CHIP?) but when I reached under there to pull the chip out the PCM burned my hand, it was too hot to touch for more than about 4-5 seconds.
^does your car have a chip?
No I do not have a chip, but the heating up of the PCM be possible. The problem did not occur until after 1 hour+ of operation the last 2 times it happened. But then again, the problem tends to disappear after a few minutes and then run OK again, so that sort of blows the overheating PCM theory. I also agree that the symptoms of the AC turning off, the trans downshifting, and the rich exhaust smell all points to an issue between the TPS and the computer. It seems like you are connecting the exhaust or rich exhaust smell to the TPS WOT condition for the first time... I could not make the correlation to the exhaust smell and a WOT signal. That would tend to make sense IF the TPS sensor is directly responsible for the fuel mixture, but I would think that the MAF would "disagree" with a funky WOT signal and the fuel mixture would remain constant. There is no real stumble when it downshifts, it continues to run pretty smooth. I would pay hundreds at this point to find and fix this problem, anyone good with the Mark viii in the Casa Grande / Phoenix / Tucson area? I am almost ready to wave the white flag...
this wouldn't be the first time that a chip was found where it was thought there was no chip..it does happen from time to time.
Pull the PCM down and make sure the access panel on the back side is still in place.
it's opposite of where the wire loom plugs in. its about a 2X3 opening.
Just verify it's still covered.
Pull the PCM down and make sure the access panel on the back side is still in place.
it's opposite of where the wire loom plugs in. its about a 2X3 opening.
Just verify it's still covered.