I've been having some problems with my '91 Z28 5.7L.....
About a year ago I was washing under the hood at the car wash (I know... I know....) and later that night, she started running rough. It surged and stalled out as it was going down the road, but not enough to actually kill the car, or if it did, the momentum was enough to re-fire the car. The check engine light came on and I had her "plugged in" and it came back with low TPS voltage. I went thru my factory service manual and did all of the checks on the TPS and found that the ground wire at the TPS is at 8 ohm and it is not supposed to be any higher than 5 ohm. The service manual said to check the grounds in the electrical system. I checked the block to firewall ground strap and it was cut. I fixed that, but am still having the same problem.

Does anyone have any ideas of what may be wrong or where the elusive grounding problem might be? Can I just tap into the TPS ground wire and take it to a body ground to solve the problem? I would prefer not to "rig" it like that. I would prefer to fix the problem, but if it get's it running right while I fix the problem, I'm game!!!!

Thanks.......................

 

There has been much discussion on the topic of 'ground offsets' on the DIY Prom forum. Basically if you use different ground locations for critical sensors you can get the feedback signals to the ecm out of wack. So you want to use a common ground for all the feedback sensors, anything that is using a 5 volt input with the varaible output to the ecm.
Check the ground at your MAP, if it checks O.K. try tying into it from the TPS to see if it fixes your problem.

 

I think the TPS and the MAP share a common ground from the ECM on a '91 '7730 SD setup. I don't have my diagrams with me at the moment, but I thought that there was one ground output from the ECM that splits for TPS and MAP. I remember this only because when I repinned a TBI harness, there was the option then for providing two independant grounds from the ECM for each sensor. I'll try to look it up later and double check.

 

If that ends up fixing the problem, then what is the problem in the first place. Although this is gonna make it run right, I do eventually want to track down the actual problem and fix it so as it doesn't affect anything else.

 

Well, lets start with the 'low TPS voltage' can you expand on this?
Three wires in, one is 5 volts, one is ground, and one is feedback to ecm which should be around .53 volts when adjusted correctly at min air on the throttle body.
Describe the low TPS voltage you are referring to.

Have you checked grounds on any of the other sensors? Are they showing less than 8 ohms resistance?

 

Got your back Thirdgen88,
TPS and MAT are grounded together at B5. Might just be a loose pin in the connector.
Coolant Temp and MAP are grounded together at B6.
If they both read a little high then maybe check the grounds from the ECM to chassis at A12, D1, D6, & D7 to be sure they are all good. That should be all of them.
Just happen to have mine handy.

 

I'm bustin out the service manual today to check where all of those grounds are at.....

Rebuild man..... I had the car plugged into a service computer and it came back with some codes. I don't remember the exact code.....22 or 23 or something like that. The computer showed low TPS voltage....aka the voltage that was being received by me ECM was low. The wires at the TPS are correct. Mine has the 5 volt wire and it reads 5V when taken to a body ground. The feedback wire is reading low voltage due to the fact that the ground at the TPS appears to be bad or have come loose.

I am gonna have to check those connectors today and search and search for the grounds.....

 

Just a thought here: If your car ran fine before the washing I would find it hard to believe that spraying water on a ground connection, wire bolted to something, would change the resistance. What I would believe is that something happened inside the TPS itself that would cause the resistance to go up. Focus your attention on that item first.
With everything hooked up and power on, key to run, back probe the TPS with a volt meter and check the voltage to ecm, what are you getting?

 

One more thing to try, if you look for the grounds but can't find them easily, try creating a new one to see if problem is corrected. This can be a temporary jumper wire, if the voltage to the ecm from the TPS goes back to around .53 you are on the right track.