OldCelica

This one is making me lose my hair at the young age of 25!

1991 Chevy Camaro, 3.1L V6 MPI

Here are the current symptoms:
-Code 42 EST (No check engine light though with this code. All other codes seem to turn the light on by disconnecting sensors except the below code)
-Code 12 will not set when trigger wire is disconnected
-High idle (2k or so)
-Missing at all RPMs
-Stalls getting to a stop sometimes
-Car drives, but not drivable
-Running RICH (You can smell it and black sooty deposits on plugs)
-Driver's side bank of fuel injectors getting pulsing signal (By this I mean that they are pulsing properly, but go from a weak to bright pulse with the noid light)
-OP-DATA on scan tool (Only things that are out of whack)
--TPS voltage in spec, but voltage jumps around a little at idle (.64-.7)
--TPS open % jumps between 1%-4% at idle
--Spark advance jumps from 24-40 on the scanner (10 steady with a timing light and signal wire disconnected)

Here are things that have been checked:
-Spark plug wires are new (Less then one year and checked for resistance)
-New spark plugs
-New Cap/Rotor
-No vacuum leaks
-Timing does advance normally when revved and checked with timing light.
-TPS, IAC, MAP, CTS, EGR, O2, EST, PU-Coil, and coil all test fine.
-Fuel injector resistance is in spec on all
-Fuel injector wiring harness checked for shorts and continuity
-ECM has good ground
-No visual signs of wire harness damage

The back story:
-Started missing once engine was up to operating temp.
-The issue was determined to be the PU-Coil.
-Replaced whole distributor (I am lazy and did not feel like taking the distributor apart).
-Engine barely ran.
-Got a code 42.
-Replaced distributor again (Under warranty. Assuming that the issue was the EST module).
-Same thing.
-Traced issue to shorted (Not completely) fuel injector (driver's side).
-Replaced fuel injector.

It ran great for three days. Parked in driveway one night. Next day starting having issues above.

Going to replace the ECM as it is under warranty as a last ditch effort. I replaced it less then a year ago trying to troubleshoot what turned out to be a fuel pump (Never borrow a friend's fuel pressure gauge). I am not optimistic though.

I need to get this car running ASAP. Does anyone have any ideas on where to go from here? I'm stumped at this point and am now at the end of my DIY in the driveway knowledge.

OldCelica

Replaced the ECM yesterday. No change like I thought.

Looks like maybe a wiring issue. Any ideas on where I should start or what specifically I might be looking for?

I have two schematics that contradict each other. I want to check the wiring for the injectors first. The ground wire for all the injectors is pink/black. The signal wire for the drivers side injectors is green. Passenger side is blue. These colors match on the other side of the harness at the front of the engine. I also have these colors going into the ECM. This matches one book but in another book I have the colors change at some point. I can't remember what colors they change to, but I have those at that ECM side as well. Can I unplug the ECM, jumper the wires in question and figure out what is what to be sure without damaging anything? I guess I could disconnect the battery to be sure. Or does anyone know for sure?

OldCelica

Sorry to be a bit pushy, but I need to get this car running by the weekend if at all possible. I have had a rental car for over a week now due to this problem. I probably could have paid a mechanic to do the work on the car with what I will have paid for the rental I typically don't let anyone touch my baby but me. In this case I am reconsidering. I am completely stumped.

(End vent)

TheScaryOne

iTrader: (3)

Observe your throttle while the TPS jumps. If you know it's not moving at all (maybe a bad spring in your throttlebody?) and the TPS is moving around, it's bad and should be replaced.

Other than that, the only wiring schematics I have are for a 87. :/ You might want to check Autozone's online repair manuals for a schematic. You might get lucky.

If you can, try setting up a temporary big three (large gauge wires from alternator to batt +, engine to chassis, and ground to chassis.) and see if your problems get better or worse.

Iceeyes

I have exactly the same type of car with exactly the same issue. I am ready to scrap the v6 and go with a v8. But until that time any knowledge to fix this issue would be greatly appreciated

OldCelica

Thanks for the info! I didn't think to check the connections from the batt and alt. I will check that.

The TPS is good. I have a scanner that reads the opdata. With the key on and engine not running it doesn't jump around at all. Even when someone bangs on it a little with a screwdriver handle. I do have another '91 Camaro with a 305TBI. The TPS LOOKS the same. I'll cross reference the part numbers and verify, but I will try that before buying a new one.

I forgot to mention above, but I did check the butterfly in the throttle body. It is relatively clean and doesn't flop around at all. Return spring still nice and tight.

rgarcia63

I can only comment on the subject of missfire (for what it's worth.) I knew my problem was spark related, but all my ignition system is high performance, after much thought I decided to change the wires because they're the most common source of ignition failure. I've had MSD, and Crane fire-wires and still experienced misfires.
I found a wire fabricator, Kingsborne "Wire Werks" who promised me that low resistance wires don't have the OEM recommended resistance of 300-800 ohms per ft.
I had him send me a custom 8mm set, problem solved.

OldCelica

Ahhhh, the schematics on AutoZone.com are SOOOOO much easier to read then the manuals I have (And I have to read schematics everyday at work). They also seem to be more correct. I have noticed a few things that I need to check and double check with the wiring.

What are the symptoms of a bad air temp sensor? I noticed that that is in the same circuit as the TPS. I'm thinking that if it were grounding out if that would give me the weird readings on my TPS. I think I would be getting a code though right?

Anyway, I have some things to check out over the next couple days. Any more suggestions would be much appreciated. I'll let you guys know what I find.

TheScaryOne

iTrader: (3)

Bad Air Temp on a V8 defaults the sensor to -40* C, which then proceeds to richen the bejeesus out of your fuel mixture to compensate for the air temp. I'd think on a V6 it wouldn't be too terribly different. It's usually driveable though, but really rich.

OldCelica

Well, I don't know what fixed it but it is fixed (For now).

I disconnected the fuel injector harness and tested the wires. They were fine. I tested the air temp sensor and it was fine. Plugged it all back in and now it seems to be running more or less fine.

It doesn't run rich or miss anymore. The TPS reading doesn't jump around and no code 42 anymore.

The only thing it does now is if you come to a quick stop it sputters slightly and then goes back to a regulat idle. This is an AT BTW. Any ideas?

I need to recheck the timing, but if she is off it will only be a degree or two. I'll drive her around this weekend before relying on her to get to and from work. For now she is drivable.

OldCelica

Well, she started running worse before better.

She started not wanting to idle at all. So long as you were on the gas she was fine, but would not idle. It got a new TPS just to make sure that it was not the issue. It will eventually go out anyway right It was still not giving a correct reading. New one did not help. I started tracing wires and checking resistance etc etc. Did not ever find anything wrong. I still have .72 volts on the TPS, but now it is reading that as 0% open instead of 5% like it was when it was running bad.

Right now it is running perfect, but I think there still may be something going on. Any ideas?