97TAMONEYPIT

Hi, this is my first post. Thanks in advance for any help. I own a 1997 Trans Am, with an LT1. It has many mods, including Cam, hollowed out cats, custom tune, lifters, ported heads I believe, etc. I had the motor rebuilt by a professional local shop with a good rep 900 miles ago, and the car has been a headache. It has ran well for the last 900 miles, however, recently, it now runs terrible. It hard starts, runs rough, and smells of raw fuel. Was running great. No codes, but mechanic says the fuel readings show its trying to compensate and dumping fuel. He is trying to tell me the PCM is most likely bad. I have googled this problem and seem to find MANY links with similar issues, but almost never a solution. It was running VERY poor, right from cold start, where it was very rough and wouldn't;t idle, and needed a good 5-10 second crank to start and maybe some gas pedal. Usually it fires right up. While mechanic was testing it while running, it made a "pop" stopped blowing as much black smoke out of the rear, and starting running "better" but no where near correctly or "good". I have 5 kids, 6 if you count this money pit, and really can't afford to just throw parts at it. Optispark, plugs, wires, O2 sensors were all replaced since engine rebuild or during. I am going to check for melted wiring etc, but wanted to reach out and see if anyone had an answer to this magic problem that seems to haunt LT1's before I drop too much money I don't have on a PCM I'm not convinced I need. Thanks again for all the help, if I forgot to mention something that helps, let me know. Thanks again.

97TAMONEYPIT

And Pacesetter headers, borla exhaust, again, was running great, then out of nowhere this, and no SES light.

Injuneer

Have you checked the fuel pressure? Have you checked the fuel pressure regulator vacuum line for wet fuel? Did your mechanic check the coolant temp sensor in the water pump?

97TAMONEYPIT

I believe he did check the fuel pressure, but I will triple check with him. Water pump was replaced during rebuild, and coolant gauge works correctly, not sure if that means its ok or still need checked. Upon further inspection in the engine compartment, looking for the passenger side O2 wires, came across two harnesses sitting on the headers. One looks to be near the back passenger side exhaust header, is a two wire that runs up near two connectors on the passenger fender, is a twisted green/orange or green/brown see pic attached, and runs into the loom going towards the fusible links by the battery junction. The other is a larger harness sitting on the middle two exhaust headers passenger side, and looks to run into a larger loom up by the pcm, that connects to the main harness that runs across the top back of the motor. I took pics but I guess phone didn't save them. This harness would be about dead center, maybe a little rear of the inside of the wheel well, running up to that back passenger corner. Any idea what these harnesses are? I moved them, reconnected the battery, and it fired right up, but still wasn't quite right. Let me know your thoughts, thanks again for the help.

97TAMONEYPIT

more pics of wiring on headers

Injuneer

There are two coolant temp sensors. The one in the driver side head if for the gauge, and doesn't affect how the engine runs. The one in the water pump feeds the PCM, this is the one you need to check. Gauge can work fine, but faulty circuit on the water pump sensor can cause the engine to run rich, if it's telling the PCM the engine is cold, when it isn't.

Here's a 1995 harness. Your 97 would have additional connectors for the EVAP vacuum switch, the two after-cat O2 sensors, and the crank position sensor. None of those should be causing your problems. A pre-cat O2 sensor shorted to ground could cause it to run rich.

1995 Z28 A4 Engine Harness

I'm not in a location right now where I can access my factory manuals and check the specific wires you mentioned.

97TAMONEYPIT

Thanks so much for the help. The harness wedged against the header contains the ground for the pcm, a knock sensor wire, and the precat RH O2 sensor wires. At this point, after showing my mechanic the pictures, we believe this harness is arcing/shorting to ground and is the cause of the problems. My mechanic has offered to fix it, I will update on whether this was the problem or not. The help is REALLY appreciated, thanks for taking the time to read and respond!

CamaroSS30thAnn

This is very interesting. I seem to be having the same problems in a way and I can't figure it out. My harness does not make contact with the headers but is very close to it. I can't remember if If it started after I took my starter off to do the plugs but I did move that harness around a little so maybe it disturbed the wires inside.
I can see the heat sheidling keeping heat out but maybe not as much as the headers put off
I also did hear some knocking noise coming from that side of the motor which sounded metallic but could have been arching wires.
Keep me updated
Mine is a 97 also

97TAMONEYPIT

So, wanted to update on this. All wiring near header fixed, no change. Mechanic checked under fuel rail, found 2 injectors leaking bad and one seeping. Replaced all injectors, runs great again, sorta, BUT, just threw SES light after 16 miles, so will need to recheck some stuff. Was told it didn't throw SES light with injectors due to custom tune on ECM to eliminate misfires due to Cam....if this helps anyone else.

Injuneer

The leaking injectors should have been picked up when the fuel pressure was checked. Always check the pressure when the pump primes (engine not started) and watch how fast the pressure drops. One of the four main causes of rapid pressure loss is leaking injector(s).

97TAMONEYPIT

Final update on this, at least for now lol. SES light was unrelated, purge solenoid blew cap off again and needed replacing. Seems the injectors fixed this poor running issue as the cars runs better than it has in a long time.