I've check all i can think of and am unable to come up with any leads anywhere.

Here is the situation,

After rescuing this old, and immaculate montero from someone for $500, I put in a new ecm, clean injectors and rebuilt all of the brakes, it went from a non-running truck to a really well running one. I thought this has to be too easy, but everything seemed to be in great shape.

Well, i was driving down the highway at 55mph, and my truck died, it looked as if the ECM had taken a crap on me, no check engine light or anything. I check it out and see I am getting proper referance voltage in, but I was getting absolutely nothing out, no diagnostics, either no or minimal voltage out. So i sent in the ecm under warranty to get it rebuilt, they send it back and i plug it in suspecting that it would work, well it didn't, so I throw a fit, and send it to another rebuilder, well after spending a day on their test bench they could find nothing wrong. I suspect maybe they fixed a loose pin or something and didn't say anything. Well i get it back today and plug it in hoping it works. I plug it in and have same condition. My truck acts like the ECM is not there. No check engine light, reference input, but no voltage or diagnostics out.

Anyone have ideas???? I was thinking ECM relay, but before i go buying more parts or tearing stuff apart I was hoping for another opinion.

Thanks ahead of time for your help.

 

Did you check your wiring harness and connectors?

 

Check your fuses and the mpi relay.

 

youre probably ruining each ECM when you install it due to a short circuit.
most likely the idle control motor has failed.

 

Would you mind explaining how an iac would cause this?

 

there are 4 coils in each IAC motor. rated at 30 ohms a piece (the updated ones are 45), the average current flow would be about .3 or .4 amps.
when one or more of those coils short circuits (anything below 10 ohms usually does it), your current flow suddenly can rise to 2, 3, even 5 amps depending on the severity of the short. The driving transistors cant deal with that much current, and melt.
when they melt, they often take out part of the circuit board with em. especially on older monteros.
this was a very common issue on any mitsu from roughly 89 to 99, depending on the model. Hence the reason for the redesigned IAC motors (now made of plastic with a higher resistance, and better insulated coil wiring).
Ive probably repaired 500 or so. the first symptoms are usually goofy idling problems. but people ignore that, and let the problem get worse until the ecm is fried.

 

Thanks for the good info manybrews.