I'm tryin to check the voltage on my tps, but the reading I am getting from the signal wire is less than 1/10th of what is should be. With the tps adjusted all the way up, I can't get it over .04v, when the reading should be around .54v. If you can please help!

 

Koeo what is the voltage on the grey wire ?

 

Ground to positive battery terminal shows 12v, signal to ground shows 5v. With throttle not depressed, the middle blue wire only shows 0.05v, and maxes out at 0.24v at wot. Not sure what to check to figure this out.

 

Replace the TPS sensor as that's what I had to do.

 

Disconnect the plug , ,probe the TPS terminals
The Gry / dark blue wire positions ?

Should see a steady change in resistance (ohm scale ) when you move the throttle through it's travel.
If not ,TPS is kaput

 

the tps is still good I already resistance checked it and everything looks good. The resistance climbs steadily as the throttle opens. I have a feeling its something else. One question my dad brought up was if the 88 tpi tps was different from a 92 tbi tps. The car came as tbi and was converted by the previous owner and rewired using an 88 harness.

 

I'm a little confused here just want to clarify....

You measured the Grey wire to ground and got 5V (with the TPS connected?)

You measure the Blue wire and get from .05V-.24V depending on throttle position?

The way the TPS works is the ECM applies 5V to one side of a variable resistance and depending on the position of the throttle varies its resistance from 0 to 100%. The voltage output on the blue wire also varies. From 0 to 100% of the supplied voltage (5V). If you do not see this as you say it means one of the following. You have a bad connection, 5V is not being supplied from the ECM, bad TPS ground, a short circuit, or the resistance while increasing steadily does not increase from 0 to 100% of the total resistance.

You need to....

Confirm you have 5V on the gray wire
Ohm from the black wire to ground confirm it reads 0 ohms
Clean your connections
Re-measure the resistance confirm that the resistance range sweeps across the total resistance

Also if your electronics are from a 1992, you do not need to adjust the TPS. The ECM internally adjusts automatically.

 

I am getting the 5v between the grey input and ground, and i am getting the correct battery voltage when I connect the ground to the positive battery terminal. The car is a 92, but all the engine electronics are for an 88, which makes things really confusing. There are not drops or jumps in the resistance as the tps is opened to wot, but I'm just not seeing the correct output voltage to the blue wire. I am swapping in a brand new tps and will update shortly if that works.

 

I just replaced the tps, the reading is now better but still way too low. at idle (no throttle) the most I can get the sensor to read on the blue wire is 0.11v. at wot, the most it shows is about 1v. I know the value at idle should be 0.54-56ish, anyone know what it should be at wot?

I am going to check the reading at the ecm and see if there is any difference in voltage too. Will report back soon.

 

Update: checked the voltages at the ecm and I am getting the same readings as from the tps. I swapped in an 88 tpi computer I had and there was no difference. I have no idea where to go from here

 

The below diagram shows how the TPS sensor works. If you have 5V on the Gray wire and a good ground on the black wire the 5V input will be distributed across the TPS sensors resistance. The blue wire is connected to the wiper that just taps off voltage from whatever point its touching. It should sweep roughly from .5 to 5V. If the TPS is new and you have 5V on the gray wire it means either your connector is bad, you have no ground on the black wire or the blue wire is shorted. Ohm the black wire to ground confirm you have 0 ohm. Also ohm the blue wire to ground you should not have 0 ohms.

 

Youngs92, Disconnect the MAF wire and check voltage on the green wire in the middle (Terminal C.) It sounds like something is draining the ECM. This will give an independent look to see if a drain is overall to the system and not isolated to the TPS ckt.

With KOEO, probe A16, C16 and B1 and voltage at the battery at the ECM. What are the voltages on these four?

Next, you can make a jumper wire with alligator clips on each end and use it to create a new ground to the ECM. I have found this to be a good tool when hunting down a very similar issue that remains unresolved.

Another potential issue would be the grounds on the back of the cylinder heads. I would suggest checking the grounds on the back of each head...broken or loose.

Here is the service manual for the '88. Good information in there related to wiring. Select regular download.


You are not supposed to ohm check these as they are solid state circuits and will cause damage! Diagnosis is done by voltage drop tests.

 

Thanks for the suggestions, I won't be able to get to them for a few days but I will report back when I can. The way my car was acting I thought the MAF might have something to do with it but it seems to be running alright now except for the idle. I reset the idle using the method in my manual to 600 rpm and it ran great for 20 mins or so. Left it overnight and went to drive it to work in the morning and it was idling around 2100 rpm and I couldn't get it to come down at all. I reset it again and am going to see what happens tomorrow morning

 

I was under the impression that 91-92 cars didn't have an adjustable TPS. If it ohmed out right you may have a wiring problem? Probably not the case, just trying to throw ideas out.

 

I believe that 88 and up had adjustable sensors. Would a short in the signal wire (blue) for the tps result in a lower voltage reading than expected? If so, how would I find the short? I know that it's not anywhere between the tps and the ecm since the voltage readings were exactly the same between the two, what else could be influencing this low reading?

I appreciate any suggestions, keep em comin hopefully we can figure this out

 

Yes a short on the blue wire would cause near 0V readings. If the blue wire is shorted to ground then the blue wire is at 0V potential (not truly 0V as the wire itself would have some small voltage drop across it). To prove this you could measure the resistance to ground on the blue wire or cut the blue wire at the TPS sensor. Cutting the blue wire at the TPS would cut out the short and you should see a normal output again.

 

I can't explain this but I took the car to our mechanic and he had no problem setting the tps. My voltmeter showed .11v, when he got it he said it was at .84. Anyway, the tps is now set, and I was told to swap out my 92 computer with an 88 with a prom for a tpi engine. I did this and the car drives much better, but it doesn't really know where to idle and occasionally gets stuck around 12-1300. If I shut it off and turn it back on then it resets to 7-800 where I set it. Any idea why it might be doing this?