94' Cutlass 3.1 L82 ECM Issues?

[ezobens]

All,

I am trying to troubleshoot an issue on my 94' Cutlass Supreme SL that I just bought last week as a daily driver.

The issue I am having is that the engine seems to be low on power, but it starts up fine, idles fairly well at 750 RPM and doesn't smoke, knock or anything else weird. The car has 89K and was driven locally by a woman that probably never drove it over 50 MPH.

What is strange is that when I accelerate from a stop, the thing runs real rough but once I get up to speed it runs pretty smooth. At first I thought I had an ignition miss so I replaced all plugs, wires, ICM and Coilpacks- But that didn't help any.

As I was trouble shooting, I noticed that the "Check Engine" light works properly (comes on with ignition but goes out when the engine is running) but when I started unplugging sensors under the hood, the car doesn't run any differently AND the "Check Engine" light doesn't come on- Very weird.

The only sensor so far that I have unplugged that turns the light on is the throttle position sensor- But nothing else.

These sensors are what I had unplugged ALL AT THE SAME TIME while the engine was running and I could see no noticable change in engine behavior:

EGR-

Cam Postion-

Idle Control Valve-

Oxygen Sensor-

Crank Position Sensor (x3)-

 

I know the Cam and Crank postion sensors won't turn on the light, but the EGR, Idle Valve and the Oxygen Sensors should have!

After all of the above, the only thing that turns on the light is the TPS.

My guess is that I have some sort of ECM or wiring harness failure that is making this car run in "default" mode where it just is running on default system values but the computer isn't really controlling the engines ignition, fuel etc.

Am I barking up the wrong tree here?

Has anyone else experienced similar issues?

BTW- I also verified all the fuses are intact and good and the fuel filters have been replaced yearly and the fuel pump is less than a year old.

ANY suggestions or advice would be greatly appreciated!

Thank you-

Elm

 

[AWeb80]

i'm gonna have to fall back on my old Seafoam practice. Pick up 2 cans and give it a shot.

 

If it hasn't been driven fast every, that means in prolly never got really hot and then has alot of carbon built up in the engine and intake.

 

here is some good info.

 

 

http://www.seafoamsales.com/motorTuneUpConsumer.htm

 

 

 

 

and how to use seafoam

 

http://www.seafoamsales.com/motorTuneUpTechGas.htm

[ezobens]

Thank you for the tip-

But I don't see how carbon build-up would affect the way the ECM is managing the engine?

The plugs I pulled were clean and the EGR is new. I agree a little highway 'soot blowing' is in order but I don't see it being my soul source for this behavior.

I can Seafoam and Techron this thing all I like (and I will try it), but I honestly think there is something more than a carbon build up issue.

Any other suggestions?

 

[Brian P]

This is the type of ECM that will not give you an instant code when something is unplugged. I temporarily ran without an EGR on my '95 (same ECM and engine setup as your '94) I would not get an EGR code until after driving it 20-30 minutes or more. At idle the EGR isn't used, and the PCM doesn't check if it's there until it wants it open. Unplugging the IAT sensor on the air box will usually give a code within a couple of minutes. But anyway. What kind of roughness are you experiencing? Although I don't agree with the "seafoam cures all" idea, if it were my car that'd be one of the first things I'd do is run a can of GM top engine cleaner thru it. Only because my mom treated her Olds Cutlass similar to how your previous owner ran it, and there were heavy carbon deposit problems. When I drove it for myself and got on it, some black smoke exited the tailpipe and it pinged. When I cleaned the engine with the top engine cleaner, it was a smoke show like I never seen before. She may have been using cheap/old gas too.

[AWeb80]

yeah, i might have been too "forward" with the whole seafoam idea, but it does help alot.

 

i've personally seen 4 cars it has helped w/ idle, accel, and smoothness.....all after plugs, wires, egr and such was changed or checked.

[SigEpCutlass]

Welcome to the wonderful world of OBD 1.5. To my knowledge, you can only go to the dealer to see if it's throwing any codes when everything's all plugged in correctly. If it were a '93 and older or a '96 and newer with either OBD 1 or 2, you'd be able to use a scan tool. If there's a problem, knowing if the computer's throwing any codes might be a significant help here.

 

Also, have you checked the injectors or run any sort of fuel injector or fuel system cleaner through the car? If all else fails, you could always try swapping in another ECM that you could pull from another 3100 '94 or '95 Cutlass/GP/Regal.

[ezobens]

Thanks for all the feedback!

I don't doubt that I have carbon build-up but apparently it's not bad enough to affect combustion to the point of pinging. I have been flogging this thing for a couple of days (keep it in the lowest gear I can to keep the revs between 4-5K at speed etc) and I don;t have any issues with overheating, pinging or smoke out of the exhaust- But at idle, the exhaust does sound like it has a distinct miss or 'lisp' to it.

I'm curious at the OBD 1.5 comment- Is there REALLY such a thing?

I'll be bummed because I just dropped $150 on an Auto X-Ray scanning tool...

 

 

[Brian P]

I was able to scan mine no problem. As long as it scans OBD1 to show data, and doesn't just "flash the check engine light" then it'll work.

[SigEpCutlass]

I was able to scan mine no problem. As long as it scans OBD1 to show data, and doesn't just "flash the check engine light" then it'll work.

 

I guess it's the scanner then. My dad has a pretty damn expensive OBD 1 scanner, and it would not read the codes from my car when I lost an injector earlier this year at his house. Hopefully yours will work then. If it sounds like it is missing at idle, I would check the injectors, and if they are ok I would do an idle relearn. See this FAQ for that procedure: http://www.w-body.com/forum/index.php/topic,31176.0.html