99 Rodeo ECM gets very hot....

My friend has a 99 Isuzu Rodeo 4x4. The ecu gets very hot after driving it for awhile. I have replaced the ECM with one from a local certified used parts place. He has informed me that he has sprayed WD-40 into the relay box under the hood because it was not running correctly and thought it was a relay problem. He soaked the replays. The motor would start sometimes when cold. Never when hot. The computer would give odd error codes. One was saying the EMC was an operating voltage error(if I remember correctly). So we replaced the ECM Now, when cold, it starts everytime. He's left it run idle for like 3 hours. He drives it a few blocks, and it dies. Let it cool down, and it cranks right up and he can drive it a little bit again. He has inofmrmed me that the ECM gets VERY hot (can fry an egg on it, he says). Any ideas?

check ground connections as well as alternator.

the old ecm wasn't getting hot. Nor was the relays. But with the replacement one, they do. I will have him check the voltage output of the alternator, though. Any other ideas to check on while we have the hood up?

Do you still have the old ECM? If so, I'd be tempted to put it back in and go from there.

What were the codes?

One of the codes that it gave off was something about the ECM operating out of parameters. He lost the paper the codes were written on.
Also, the transmission light would come on, gas light, and several other engine codes.
I wish I could provide more information than this, I know it's vague.

Also, the transmission light would come on, gas light, and several other engine codes.


This makes me think the alternator is bad. Classic sign of a bad alternator on these vehicles is odd trouble lights. The orginal ecm might have been ok. If the alt is bad it could probably cause odd readings for the ecm.

Try turning on the fan for the heat/ac if it doesnt work then I would say definatly a bad alternator.

I vote for the alt too.

If the tranny light comes on with another light then it is typically the alt.