1G Intermittent ECU Offline

[nightracer91]

Okay, I'm having a problem that seems to be getting worse. Sometimes, when I go to start my car, the ECU does not turn on.

I first thought is it was my MPI Relay but after 3 of those I've decided something else is the problem. After looking at the Wiring diagram of how the ECU is powered by the car I think my problem may lie in the transistors within the ECU which control the MPI relay to send power to the ECU. Anybody else seen this problem?

Also, at times I can hear the relay click rapidly for a while, sometimes not stopping until I shut the key off. Even when the Relay clicks properly, the ECU still does not power up. Just looking for some guidance trying to rule out vehicle wiring from internal ECU.

Car has AEM EMS BTW.

Nobody has any thoughts? No similar situations?

 

[nctsiawd]

I had the same problem, and I'm running AEM EMS too... Mine turned out to either be the turbo timer or the turbo timer wiring harness. I unhooked the plug and play harness for the turbo timer and I haven't had anymore problems with it going offline. Never did hook the turbo timer back up. This happened about a year ago.

 

[91Bomb]

Over past 13-1/2 yrs with three 1g's I ve had quite a few ECU's go bad and some went all at once and a couple went bad slow over the course of a few weeks. I had one cause serious running issues for a full year. I thought was due to other unfound problems only to be completely shocked when it went 100% bad and replacement ECU solved all problems.

I'd open up the ECU and check caps and both sides of the board. Also highly recommend buying another used ECU to swap in and even if the ECU isn't your problem this time you'll have a good spare and test ECU around which imo is a good idea for DSM owners since these cars are all between 11 and 21 yrs old now.

 

[nightracer91]

Over past 13-1/2 yrs with three 1g's I ve had quite a few ECU's go bad and some went all at once and a couple went bad slow over the course of a few weeks. I had one cause serious running issues for a full year. I thought was due to other unfound problems only to be completely shocked when it went 100% bad and replacement ECU solved all problems.

I'd open up the ECU and check caps and both sides of the board. Also highly recommend buying another used ECU to swap in and even if the ECU isn't your problem this time you'll have a good spare and test ECU around which imo is a good idea for DSM owners since these cars are all between 11 and 21 yrs old now.

I'm running AEM EMS, I don't have the stock ECU in the car. Is is AEM's Plug and Play ECU Series 1. If it is a bad ECU, it should be covered by AEM's Lifetime Warranty.

 

[nightracer91]

Of course, now that the weekend is here and I actually have some time to work on the car, it won't act up for me to diagnose what is going on... should have expected it

 

[nightracer91]

Wow... ECU Still turns on every key cycle. Whenever I want my car to mess up it won't. I hate Murphy and his dumb law

 

[luv2rallye]

The ECU itself turns the MPI relay on which supplies power to the ECU main power pins. So the ECU may still be intermittently bad. Open it up and check for leaking caps. If the ECU is the problem it will only get worse.

 

[AWD-TSI]

I was also having a similar problem, although I am still running a OEM ECU the harness is the same. My ECU was having intermittent problems. I would touch the ECU and it would turn off.

Some times it would not turn on or the MPI relay. I checked my harness and it seemed fine. Then I checked the power feeding the ECU and it was dead. It ended up being the MPI feed that is on the battery. The one with the J-case fuse. The black and red wire going to the ECU was being pulled out.

It didn't look like it from just looking at it but if I pushed the wire back in it turned the ECU and the MPI relay on. It might be the same problem. I hope this helps.