Hit gas, car stalls. Bad ECU???

You fix one thing on these cars and something totally unrelated goes bad at the same time.

I put a new exhaust manifold gasket in to fix an exhaust leak. When I hit the throttle to back out of the driveway the MPI relay clicked and the car stalled. It fires up every time, but as soon as I hit the gas it will die or come very, very close to dying. The check engine light comes on, but never for long enough to check the code. It goes away the moment it dies or recovers.

It's been very difficult trying to find people with similar situations that were able to resolve their issues. It seems it could be a bad ECU or MPI relay? I need some advice and some places to check before I start throwing parts at it.

 

[Terry Posten]

Make sure the MAS plug it tight.

 

MAS plug is good.

Here's a few other things I've checked:

Pulled ECU and checked connectors. Everything seems to be tight. Caps were replaced by a previous owner.

Unplugged the ISC and closed throttle switch and it still does it.

I'm going to get my multi meter and test the TPS and ISC today.

It seems as soon as the closed throttle switch is opened it will die. The engine doesn't even have a chance to rev before the MPI relay will click, the CEL comes on, and it will stall.

 

Do you have a wideband that you can watch while it does this? If you can figure out what the AFR is doing as it dies it might help pin-point the problem.

 

[toybreaker]

The mpi relay dropping offline with the engine running points to an issue with the cas or ecu.

Be sure to thoroughly check the wiring harness/wires/connector at the cas for damage.

Do you have a spare cas? Might be worth swapping it out as a quick test.

If you need an ecu to plug in and test with, I've got a socketed one here I can get headed your way if need be.

 

No I don't have a wideband.

Hey John, long time no speak /ubbthreads/images/graemlins/smile.gif I don't have a spare CAS, but I can definately get a hold of one.

Something else I thought I should add. Monday the car died on me in traffic. I had the A/C and both fans going. As I was coming to a stop it wouldn't idle and died. It then had a very difficult time maintaining an 800 RPM idle with the A/C off. This is the first time I've ever had idling problems with this car. It has always held a steady idle and would fast idle when coming to a stop. Could it be the ISC died and fried the ECU?

 

Well, Mr. Terry Posten, you are the hero...and I am the complete definition of fail. The MAS plug wasn't completely tight. /ubbthreads/images/graemlins/banghead.gif

I was poking around the CAS, checking the plug and wiring, when something told me to check the MAS plug again. I blew off the feeling and continued to check other things. Later, I finally took another look at the MAS plug. I pushed REALLY hard on it and *click*...car runs great.

I'm going to go hide in a corner now /ubbthreads/images/graemlins/bawling.gif

 

[Terry Posten]

That's OK. I found a blown fuse on a friends car after he spent all day trying to fix it. He swore up and down he tested all the fuses. But I found it within 20 minutes. I figured out the circuit that was dead, traced the proper fuse and sure enough, it was popped.

It happens to everybody.

Most of the time it just take another pair of fresh eyes and to ignore what was tested before. Just check it again.

At least it is running...

 

Haha thanks for bringing up my missed fuse problem Terry.

I've actually done this with the MAS as well. I always get a check engine light fot it and instantly remember that I forgot to plug it back rn after taking it off for some reason or another

 

Yes, at least it is running.

I must admit this isn't the first time I've had issues with my MAS plug, but usually I don't plug it in at all and the car won't run one bit. This time it was plugged in, but not completely. Oh well, live and learn. Now I know and hopefully someone who has this issue in the future will find this and be able to solve their problem.

Thanks for the help everyone.