General erratic stalling and starting/MPI relay/ECU

[tyhoppy]

Ok, had this problem a while back and it stopped for a few months. The car would stall out, and not start, let it sit a few minutes and it'll start up until the next time it decides to throw a fit.

I noticed today that if it dies while cruising and I just let off the clutch to try to get it to start, sometimes the MPI relay will click repeatedly very fast, and sometimes it won't click at all. This is all while going down the road with the key on and the clutch released and car in 5th gear.

When it dies I hear the relay click a few maybe three times, then sometimes it takes longer to get it started than others. Before when this happened I changed the ECU but it did it again with that ECU. And also, While it was in the middle of one of it's fits I changed the MPI relay and it didn't start with a different relay. A few minutes later though it started.

How do I fix this problem?

 

[Defiant]

Bad electric part. Sniff your ECU.

 

[tyhoppy]

It did this with both ECUs where in my other car it doesn't have this problem.

 

[steve]

It did this with both ECUs where in my other car it doesn't have this problem.

I assume that meant you've run both ECUs in the other car to check them since having this problem?

It could be a bad connector or a bad MPI relay. Make sure that the power feed from the battery to the MPI relay isn't cutting out. Then you can check to make sure that the signal from the ECU to activate the MPI relay is good. If the relay is clattering it's not likely an issue with the power feed post the MPI relay unless something is shorting and pulling the power down to where the relay cuts out. Get out your multimeter and test them.

 

[tyhoppy]

Yes I've run both ECUs and tried a different relay. where do I check the power feed from the battery to the relay? just check it at the plug going into the relay? How do I check the signal going from the ECU to the relay? The ECU sends a ground signal to the relay, correct?

 

[steve]

Yes I've run both ECUs and tried a different relay.

Where do I check the power feed from the battery to the relay? Just check it at the plug going into the relay?

Yes, but you need to do so while using the car in the manner that exibits the problem. So you need to use some jumper clips to your meter and insert a piece of wire into the connector to get access to the feed.

How do I check the signal going from the ECU to the relay? The ECU sends a ground signal to the relay, correct?

Send isn't quite the verb I'd use. The ECU pulls the signal to ground to cause current to flow through the relay coil and activate it. It might be easiest to ground this pin to see if the problem stops (and then you can track done whats broke in this section) keeping in mind that the MPI circuit will be hot as long as the pin is grounded. You can't leave the car like that or your battery will go dead.