Hey all,

Yesterday I started up the truck after a short drive and it stalled out before I drove away. It had a rough time starting and a bad idle, and would stay running. Suspected a bad battery or alternator, so being without my tools I dropped in a new battery (mine was about due anyhow) and it hardly started, and idled erratically, then died. CEL flickered off a couple times (on due to smog/EGR delete). Towed to the shop and they have no idea, said the alternator is fine, but timing is erratic.

I have a spare ECM that I'm going to swap in at the shop tonight and hope that's the fix...otherwise I'll get towed home, pull codes and go from there. I couldn't find much on symptoms of a bad ECM so I want to start this thread for anyone else in the future. I'll keep you all posted.

Thanks guys,
-Glaser67

 

Diagnose first. Read codes. If the engine still runs, the ECM is working. It could be a faulty ECM, but that certainly is not the first thing to replace.

 

Don't ever go back to that shop if they can't be bothered to check the codes when asked to diagnose an engine problem.

 

I agree that hooking up a code reader is necessary, & that the shop sounds crappy. You might be able to rent one from an auto parts store since you can't easily drive the truck to one. I don't know much about ECMs, but I do know that a bad capacitor on the board should be visible when you remove ECM.

 

FYI - Capacitors are related to the 5vdc reference voltage. Measure this first, if the 5vdc is present, then your current issue is not related to these capacitors.

 

Sometimes. They are sort of like a flashlight battery say. Batteries that leak are always bad, but dead batteries don't always leak. If they are 10+ years old they are getting up there in terms of lifespan anyway.

 

Thank you everyone for your replies. I would like to report back:

Agreed that the shop (who has done good work for me previously) is off my radar. In order to pull codes you have to jump the STI wire that I put in the main test connector to the cod reader. Simple to do, but they could have called and said they were having problems with doing it...

About all I know they did was at least verify me alternator was good. Geez, thanks guys. Other than that no help.

Back when I did the MAF conversion, I didn't bother to re-loom/tape the main harness connector where it plugs into the ECM. I suspect the rain during when she was acting up might have caused the issue.

So I grab my code reader and old ECM, and when I go to start her up, low and behold she fired right up. I went home and taped up the connector on the firewall, and pulled the codes.

31: EVP - No surprise, whole EGR is blocked off and disconnected.
41: System lean - I'll dig into this one
91: System lean - System running lean, fuel control

So any suggestions for codes 41/91? Obviously I'll check for leaks, and before I re-pull codes I'll get the O2's nice and hot first...and post pictures of the plugs too.

Lastly, she has not cted up like that since I sealed up the harness connector. I did find that all 3 of my capacitors were leaking a bit on my A9L, so I'll get that handled and report back if I notice a change.

Thanks all,
-Glaser67