ECM randomly doesnt turn on!!

[Kyle Warning]

I have a 93 lincoln mark viii and at completely random times I cant get it to start due to the ECM not turning on. The reason I know this is because I try to get codes and nothing happens. Then when I can get codes the car fires right up! Once the car is started I have no problems. When the ECM doesnt turn on I just come back after a few hours and it will turn on. Please help me before I lose it!

 

[BILLBOATS]

Rule in or rule out the ecm being defective and then go buy one. If a good ecm dosen't cure it look for another cause of no start. That is after you found the ecm to be needing replaced and then replaced with a known good ecm

 

[unity]

Odd, the ECM is always on. Thats how the adaptive learning stays in place, such as O2 sensor conditions, etc. And why pulling the battery is a way to clear codes, reset the tables to factory.

So I sorta doubt its defective, but I agree on buying a replacement to swap out might be the quickest method in trouble shooting. But I feel its going to be wire/relay or ignition switch related. Because you say it does not randomly start, yet you dont say it dies when running. I lean towards a defective ignition switch - remember, the ODB port is not powered on unless the car is. So you are likely looking at a global power-up issues.

 

[joegr]

There is a constant battery feed that powers the static RAM all the time, but no the ECM itself is not always on. The processor is only powered and running when the key is turned to run or start.
I would verify that it is getting power on the switched power pin when the car won't start. If it isn't, then you can trace back to find the fault.

 

[slowmkviii]

Had this problem on a town car
About 10 years ago I believe it was a relay