Does your V6 do this... (Page 2/3)
Gall757 JAN 25, 04:33 PM


Now there is an explanation!

So you anticipate that it's some sort of grounding problem?
donuteater306 JAN 25, 04:56 PM
Good lord, carbureted Cadillac Cimerons!!! Thank gawd the Fiero wasn't carbureted!!!
cmechmann JAN 26, 07:07 PM
Those are just examples of what I have seen cause "tip in" break up.
Nah don't anticipate a wiring problem. That seemed to be one of weird quirks J bodies would get. They would get a bad connection where they put multiple wires together. Earlier ones would be in the harness where it goes along the firewall. The later ones would be around the left fender going towards the transmission. Some where so bad they would stall.
On a Fiero I would lean towards a TPS problem or primary ignition problem(corroded area where ignition module mounts) . But also disconnect the EGR. One with a weak diaphram spring could do it too and easy enough to rule out. (Causing it to open too early/easy). With that though, if it gets a little better but did not go away when disconnecting EGR, I would start looking for a fuel problem. EGR will make lean issues, seem more pronounced. Good example: cracked vucuum hose/tube to the fuel pressure regulator.
donuteater306 JAN 27, 12:13 AM
Thanks Cmechmann, I appreciate your help. Pulling the vac line off the EGR valve didn't change anything, but I haven't tried blocking off the flow yet. Funny you mention the TPS. I just went through 3 defective Delco units that I got from Amazon. Ended up putting my old one back on...but I never tested it. I know that there is no corrosion around the ICM because when I did the tune-up I pulled the dist to replace the O-ring. At that time, I replaced the heat sink compound under it.

I plan to go around the vac lines this weekend checking for leaks. What about the 02 sensor?
2.5 JAN 27, 01:56 PM
TPS and EGR would have been my thoughts.
cmechmann JAN 27, 08:37 PM
Yeah just a thought. I see a lot of older gm v6 distributors with the green or white crust around the module. Sometimes it can grow enough to cause a crappy ground and cause strange stuff.
Unless a TPS just goes out, they normally start to fail where they normally sit at. You guessed it, right at "tip in".
The newer stuff can have 4. 2 accelerator and 2 throttle position sensors for the throttle by wire cars. Almost everything from 2007 on. And yes they are showing their ugly faces. One goes out, ECM can't use the data, goes into reduced power mode.
I think I did over 10 throttle bodies on different makes last year.
Starting to see the auto start functions fail.
donuteater306 JAN 27, 10:20 PM
Ya, we have a few 08 Impalas at work. One of them had the gas pedal fail...flat out no signal. Had never heard of that before! Ahh, technology...gotta love it!

Hey, what method would you use to bench test a TPS like what's in the Fiero? We used a multimeter, and my OTC scanner on the ones I got from Amazon but two of the three would just drop the signal at closed throttle, read zero volts (the 3rd one set the SES light on immediately after starting the engine. None of these required much of a test. But if I have a bad spot just off of idle, I don't know if my multimeter or scanner will pick up that blip fast enough. How do you suggest that I test it?
dobey JAN 27, 11:56 PM

quote
Originally posted by 2.5:

TPS and EGR would have been my thoughts.



Could be engine ground strap too. Or could just be the throttle cable has stretched a little over its almost 30 years of usage.
cmechmann JAN 28, 10:37 PM
We test TPS with multimeters unless we see it drop out on data stream on a scanner. If you can use a scanner that can graph data even better. However the best way to "see" when a TPS screws up is with an old voltmeter with a needle. You can see the needle bounce where the TPS glitches out. Most of the time we can catch the drop out while in a scanner.
OK. except for early computer/microprocessor controlled cars, every TPS I have seen is a 3 wire, 5volt sensor. Very early ECC Fords used a 12 volt sensor. That kind of screwed things up when battery voltage was low.
So you have a ground, 5 volt reference from the PCM/ECM and signal return. If you have a code for no TPS or see no change on voltage, always look for a problem with the first 2. I can't count the times I have seen someone throw a TPS on and there was a broken ground. Or better, someone put on a MAP sensor and the vacuum hose is cracked.
So you know you have a good ground and good 5 volt at the TPS. It doesn't matter who's TPS it is.(except for late models with multiple sensors in the same module) If you found the ground and found the 5 volt reference signal , the last one is signal return.
Don't perform the following on a throttle by wire car without checking manual first. Do not manually move a throttle by wire throttle unless instructed to do so by service manual !!!
So. You took out your volt meter. Disconnected the TPS. Turn the key on, engine OFF. 1 meter lead on ground. Then you took the other lead and checked the 3 wires. In the connector not the TPS. 1 reads 5 volts. Unless there is a broken wire in the harness and I have only seen 3 PCMs in the last 20 years with a bad reference signal regulator and 2 of those have been smoked. next. Leave that one in the connector and pull the lead off ground and check the other 2 connectors and you should find your ground. If not wiggle the hrness around and check the engine grounds. See that one a lot. next So now you know what connectors are what. Turn key off. Plug the TPS back in. Raid a small paper clip from your desk. Straighten 1 end of it. On the wire that you haven't had anything happen on, use the paper clip to "back probe"(paper clip along wire, pushed through the seal/weather pack, to contact the metal connector inside, you'll feel it). Key on again. engine off. 1 lead on ground and the other on the paper clip. Use the other end of the paper clip, you didn't straighten, to hold the multimeter lead. At that point you should see somewhere in the range of a 1/2 volt. If not double check your connections/grounds again. If you are certain that that stuff is good, that TPS is bad. And it should have ran like crap. Now you want to watch the TPS "sweep" voltage. This can be done on a bench but you would be using ohms. And of course know which connectors. Grab the throttle and open it up just to watch its range. Nominal should be 0.5v-4.5v. If it starts too high. Look for something effecting throttle angle or weak ground. Grounds like to react different under a little load when connections are flakey. Might read OK on the earlier test but a little load changes things. Let the throttle drop back down. Do it again. You seeing if the range is consistent. If the range changes around, the TPS is most likely bad. The newer stuff seems to have this kind of fault. work, work ,work, nope, work, nope, nope, work kind of thing going on. Go up to a point and then stop changing or go back down and drop out. On the older stuff it seemed more of a bad spot. With those you sweep different. Unless you are using an old analog meter or expensive fast meter the refresh rate of the meter is not smooth. So you have to sweep them slowly. watching at each movement. You won't see the in betweens unless you are using an analog. On those you will see. up, up, buried, up ,up, up, up.
Check them both ways and multiple times.
Think of this. Small sheet of plastic with a piece of foil glued to it. You treat the foil so it turns in an oxide/rust/carbon track. If the resistance is right you can hook the ends to a battery and take a meter and as you move it up and down the track, it changes. You keep wearing in 1 spot and you wear a hole in the foil or start peeling the foil off the plastic. Or a piece of crap falls on your track and screws your reading up. Isn't amazing how well they do work?
And. When you are driving. Where is the TPS wearing itself at most of the time? Tip in?

[This message has been edited by cmechmann (edited 01-28-2015).]

donuteater306 JAN 29, 12:08 AM
That has got to be the most detailed diagnostic instruction I have ever seen! Thank you! I'm going to print this and take it to the car with my multimeter!