Newbie trying to fix drivability problem, please help!

[Wingnut87]

Hello everyone, I'm new to both the forum and Flash scan. I have been using Autotap for a while and just bought the $250 Flashscan scan only tool because I couldn't figure out what my problem is with Autotap.

I have a 1987 RX7 GXL with a 2000 Camaro SS engine swap. From the time I got the new engine running, it has run poorly. It runs great for 2-5 minutes and then it almost dies at idle and feels like it is missing under acceleration. I have checked and rechecked the O2 sensors. I even replaced them eventually and the problem persists. Autotap reads reasonable values for the two front ones and 450-900mV for the rear two (I have eliminators connected). The MAP and TP sensors check out. The short term fuel trims eventually drift towards a -40% condition. I really have no idea what is wrong. One clue may be the VSS reads 0 mph all the time, but the wiring from PCM to sensor connectors checks out. Also, my aftermarket gauge reads the speed off the sensor just fine. Can the PCM have internal problems and still run the engine? I've been racking my brain about this for months.

My Flashscan with arrive tomorrow or Monday. What do you guys recommend I do first? I have been reading the FAQ's and tutorials and have a decent feeling about the system and am excited to try it out. I'm an engineer and learn quickly. Any advise is appreciated!

thanks,
Tom

[emarkay]

Did the engine perform 100% before the transplant?

It runs great for 2 minutes ONLY WHILE from a cold start? If so, that would be while it's in open loop and using the "average/best guess" fixed tables - you could pull 2 plugs and stuff a sock in the intake and it would still run fine then!

Any possibility of pinched wires or something mechaical like that or some bad grounding issue, fuel pressure, vacuum leak, exhaust backpressure, engine misalignment or other unintended loads?? With a swap like that you need to be an engineer as well as a mechanic!

Yea PCM's can be partially dead - ask any mechanic. They can also be intermittant. Wonder if you can get a "test" PCM to - um - test? Any possibility the PCM was "LSEdited"? They are not "bulletproof", and can be damaged by mishandling, moisture, vibration and other things when not bolted to and grounded in a vehicle.

Keep us informed.

[Wingnut87]

Thanks for your response.

I bought the engine, trans and computer from a yard on Ebay. I don't know how is ran before. I have done my best to check all vacuum lines. I ran shop air into the engine and found a few clamps to tighten. I ran big ass ground straps and am getting good signals from the sensors. Fuel pressure is a steady 62PSI.

The PCM has had some airconditioning codes removed, but the problem predated any modifications. I don't know anyone who can program and "lend" me a PCM. I was hoping Flashscan might be able to diagnose a partially dead PCM. Is this possible? I have dumped enough money down this hole and don't want to buy a PCM (although I will if I need to).

I am an automotive engineer (non engine stuff mostly) and have always been a gearhead. I built three Formula SAE race cars in college. I hope I know enough not to make silly mistakes and figure this problem out, but you never know. I have found so many problems and have fixed them all thinking I solved THE problem, only to find it must be something else. I am out of ideas now. Is there anything I should log first with flashscan that might give me a clue?

thanks,
Tom

[ringram]

wait4me will sort you a pcm for peanuts if you need one. Pity you dont have the tuning version you could run open loop. You dont know what injectors and so on you have do you? if the pcm doesnt match the engine you might have an early pcm with a later model engine. The injectors were larger on later engines. But closed loop should sort that out. I think with the scanner version you might be able to download the pcm tune, if thats the case then compare it against a stock tune to make sure its stock. Also check injector flows etc. Exhaust leaks will cause wrong 02 readings. But my vote is for a 99 pcm with 01 injectors or something. Basically 26lb vs 28lb. Any chance you can borrow a wideband as well?

[Darkness]

He said the fuel pressure is at 62 psi, I dont know if that would affect it but mine is about 58psi.

[joecar]

Can you capture and post a log (include as many parameters as you can) of it running and dying...?

[Wingnut87]

I got my Flashscan today. I will try to log a run over the weekend.

thanks!
Tom

[Wingnut87]

Ok, I used Flashscan for the first time today. It seems there is a lot to learn, but the more info the better! I am attaching a log file. Let me know if there are any other PID's I need to include. The car got pretty bad around frame 52. I was mostly just idling or reving the engine. I drove around the parking lot from frame 112-120. I'm also including a picture of the car.

thanks for your help!
Tom

[ringram]

Nice. A couple of suggestions. If you keep under I think 28 or 26 PIDs you will run at 10fps, over that your sample speed drops. You are logging too much stuff. There is a default pid selection file, use that as a good startpoint. If you have specific issues like idle tuning you can make a new selection up with the relevant pids and save it.

One thing thats often used is wideband input so you may want/need to add that.

Usually map, tps, rpm, ect, iat, kr, g/cyl, g/sec which should all be in the default list should form your base as you will build maps with them to track spark and fueling.

[TAQuickness]

Given the unknown past of the engine, I would start with a compression check, then systematically check each sensor with a meter (might want to send Joecar a pm for help on this one).

I would cross reference the engine, injectors, and PCM part numbers to verify compatibility.

Verify all injector connectors are secure, verify all spark plug wires "clicked twice", verify the grounds.