92 Lesabre multiple bad TPS

OptimistPrime

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Hi. I've got a 92 Lesabre that I'm pretty much at my wit's end with. This thing has failed three different throttle position sensors. At this point I've tried two off-brand and one actual Delco model. Clearly there's some kind of fault in the wiring. Or, alternatively, the wiring is fine and the ECM is bad. I really don't want to pull this entire car apart, so I was wondering if anyone had suggestions on how to determine if ECM itself is faulty.

It's hard to see how the wiring could be bad. This car was garage kept most of its life, and only has about 40k miles on it. If the ECM went out, will any OBDI ECM from this platform of car (Pontiac/Olds/Chevy/Buick 3800V6) work? Or is it specific to the make and model?

The current TPS didn't last but a couple hundred miles. I've pretty much given up driving the car until I can sort out why it constantly fouls this sensor. If anyone has suggestions on tracking down my problem, I'd love to hear them.
 

Lubener

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"WAS" 97 Lesabre
Stop replacing the TPS because I doubt they were all bad, unless you actually tested them and found a dead spot in them.Start doing some diagnostic work, looking at the TPS connections and wiring. Mileage and garage kept mean nothing when a rodent has been nibbling on the wiring on a stored, garage kept car. You probably disturbed the wiring each time you replaced it. On some cars(not sure about yours) the sensor position has to be adjusted. If you see slotted mounting holes on the sensor, chances are it needs proper adjustment upon installation.
 

CorvairGeek

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1996, 92 Buick Century
Stop replacing the TPS because I doubt they were all bad, unless you actually tested them and found a dead spot in them.Start doing some diagnostic work, looking at the TPS connections and wiring. Mileage and garage kept mean nothing when a rodent has been nibbling on the wiring on a stored, garage kept car. You probably disturbed the wiring each time you replaced it. On some cars(not sure about yours) the sensor position has to be adjusted. If you see slotted mounting holes on the sensor, chances are it needs proper adjustment upon installation.

Those are excellent points. The Buick 3300 and 3800 have adjustable CPS and TPS through 1992 (unfortunately). Here is a scenario on an adjustable TPS; you replace it and the error clears. After some miles, the error returns because calibration is so far off after the computer 'sees' the incorrect throttle position (idle) long enough. The closed idle position need to be around 0.5 VDC, but a manual needs to be referenced for exact model and year.
At least the TPS is isn't immediately destroyed like an un-adjusted CPS.
 

OptimistPrime

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Thank you for the replies. The reason I suspected the TPS was bad had to do with the error indicated when I had a mechanic scan with his OBDI scanner. I don't have one of those scanners, so it makes the whole process difficult to pin down. Perhaps it was faulting not because it was bad, but because it was out of adjustment. However, one of the TPSes was a professional replacement, and the shop claimed they did calibrate it. The car started acting up again a few months later. The other ones I replaced myself, and they weren't calibrated because I have no idea how to do that. In both cases the car did run better for a while. The check engine light went off. Like I said, I don't know how to calibrate it, but I know it was at least installed correctly.

I don't know what else to do other than try to find the bad wire, if there is one. That's going to be difficult, and I probably will wish it was something easy to swap out like the ECM. This car has had other strange sensor problems. MAF went bad, O2 sensor went bad, and of course the TPS. The mechanic who replaced the O2 sensor claimed it appeared to show very little wear. The MAF I pulled out of it had very clean elements. In general, everything under the hood is about as clean as you're ever going to see for a car this old.
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OptimistPrime

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Sorry to bump this old thread, but we've only just now started having weather that's good enough for me to stand outside and work on this car. I traced back all the wires from the TPS/MAF etc to the firewall, and everything seems fine in that regard. All the wires are practically new, and have never been taken out of their little black wire wraps. I pried them open along the seem and peered in there, and didn't notice any fraying or cuts. I pulled the plastic cover off the relay, and that's where I discovered my first actual sign of trouble. There are several relays in there that clip into place, side by side. One of my relay clips is broken, causing the relay to hang loose and bang against the ones next to it, which in turn knocked them loose. I'm off to the junkyard to salvage a replacement, but I'm wondering if this would even cause the issue.
 

HotZ28

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1996 Roadmaster Limited Collectors Edition 58k - 1996 PAU 2019 Regal GS
One of my relay clips is broken, causing the relay to hang loose and bang against the ones next to it, which in turn knocked them loose. I'm off to the junkyard to salvage a replacement, but I'm wondering if this would even cause the issue.
The relays on the firewall panel has nothing to do with the original problem! Set the TPS with an VM to NO more than .38-.42v @ the closed position, otherwise it will be out of calibration. We have some post in the archives/search on how to do the wire voltage test. Do a search in both PA and LaSabre forums.
http://easyautodiagnostics.com/gm/3.8L/how-to-test-the-throttle-position-sensor-1
 
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