Anyone Seen a Smoking ECM Before?

[HotRodPC]

Have you got a good digital volt gauge? Check your voltage just for ***** and giggles. You should have between between 13.2 and 13.8 to be safe. If it's 14 or higher, you need a new voltage regulator. You might be cooking ECMs. Check it right off the alternator wire. And rev it up too. Don't settle for it's good at 800 rpm while idling. Watch it as you rev up to about 2000 rpm or so.

 

[1987 GMC Jimmy]

While I'm the first to be suspect of a remanufactured ECM, this is sounding a little suspicious.
Service Engine Soon light and any codes?
The correct procedure before replacing an ECM (according to the shop manual) would be to check each pin for abnormal connection to power or ground that could cause damage. This is easier said than done, and does require the schematic. It wouldn't rule out an intermittent short either. All I can suggest is a through inspection of the entire ECM harness, which isn't easy either.
Another thing to be aware of is that most consumer soldering irons / guns are not remotely ESD safe. They can develop damaging, high voltage (to sensitive electronics) at the tip. It would be best to unplug the ECM, Electronic Spark Control Module, etc., anytime a wiring repair is required.
As a last resort, if you can get a good enough look (I know it is not easy and may require some disassembly) at the ECM to see the area that is damaged, AND see enough of the traces to where they connect to the harness, you could give that area of the harness a very thorough inspection for any abnormality.

I'm glad you told me that about soldering irons, and I'll unplug the sensitive stuff from now on. For now, there are no visible wiring problems. And I haven't gotten any codes in a while. I'll probe the harness for out of spec voltages, and I'll see what I can find. As far as tracing the circuits go, I can already tell you that the EST/ESC circuit usually fails, the diagnostic circuit always fails, and the MCS circuit failed once. This time the spark control circuit failed last night, and after some driving the next day, the diagnostic circuit failed. The MCS circuit and various sensor controls appear to be working this time around, as they usually do when this happens. You're right. Something's gotta be wrong here. I disassemble every one of these things when they fail. The original had a visibly burned integrated circuit, and it was just completely dead. Every time this happens after that, I can't see any visible burns in any of it. I've just seen the smoke and smelled the scorched on the actual board when it happens. I've about lost count, but this must be the seventh or eighth ECM I've gone through. The one I got in December worked great for about 4000 miles until it got wet a few days ago. I've only noticed a few electrical abnormalities. I'll sometimes get a Code 54 (MCS short) when I jump A and B, and the solenoid will start clicking at twice the speed. It'll quit when I undo the jumper. There's also a single underhood connector I haven't accounted for. I've noticed that if I physically pull on it, the compressor clutch will engage and hold as long as I hold. If I let go, so will the compressor clutch. The compressor clutch will also erratically engage/disengage once in a while. This is the only thing I've really noticed during normal operation, and I guess it's worth mentioning because the ECM gets a signal whenever the clutch engages. I'll attach a picture of the connector I'm referring to.

Have you got a good digital volt gauge? Check your voltage just for ***** and giggles. You should have between between 13.2 and 13.8 to be safe. If it's 14 or higher, you need a new voltage regulator. You might be cooking ECMs. Check it right off the alternator wire. And rev it up too. Don't settle for it's good at 800 rpm while idling. Watch it as you rev up to about 2000 rpm or so.

I do, and I will. That's a great idea. If that turns out to be it, I'll be so relieved. Thanks!

 

[CorvairGeek]

Excellent idea on voltage. Alternators can also fail and put out AC along with DC, but they are typically noisy and very hot when this happens. I can tell you from experience that the power windows are really fast with 16+ volts too!

That looks like it should plug into one of the A.I.R. valves, I believe that is one one right behind your hand.

Being able to pull on the wiring and engage the compressor sounds like when the main HVAC connector was melting on my car, and the repair we discussed off line. I was getting intermittent compressor engagement as the large gauge wire heated and turned in the connector.

 

[HotRodPC]

On a non ECM controlled vehicle, I had a buddy that couldn't figure out why he was always burning out light bulbs. Dash lights, interior lights, tail lights etc. Votlage was 14.8 at idle and 15.5 at about 1200rpm and above. Not to far out, but thin filaments are less tolerable. ECM's are too. Running them a little hotter will cause components in the ECM to cook. Even higher voltage might get them hot enough to melt solder. Just figured it worth checking out since it seems to be an ongoing problem here. Voltage regulators don't always go bad to the low side. I've even seen in my own truck before one just lost voltage regulation all together. Damn was my headlights bright at 2500 rpm. The more rpms the higher the voltage. I could sit there and see it on my Stewart Warner Volt gauge. At 3000 rpm in the 4.56 gear truck, the volt guage was pegged.

 

[1987 GMC Jimmy]

Have you got a good digital volt gauge? Check your voltage just for ***** and giggles. You should have between between 13.2 and 13.8 to be safe. If it's 14 or higher, you need a new voltage regulator. You might be cooking ECMs. Check it right off the alternator wire. And rev it up too. Don't settle for it's good at 800 rpm while idling. Watch it as you rev up to about 2000 rpm or so.

You were right! 15V at idle coming right off the alternator. I don't even want to know what was happening at 2000-3000 RPM. So I guess the voltage regulator on the ole Delcotron is bad. What do I need to do to fix it? No wonder my headlights were brighter than my mom's '02 Suburban's at night. Ahh, I guess you can't win them all. Thanks, HR, for telling me about that. I never would have thought about it.

That looks like it should plug into one of the A.I.R. valves, I believe that is one one right behind your hand.

Being able to pull on the wiring and engage the compressor sounds like when the main HVAC connector was melting on my car, and the repair we discussed off line.

You were right! Plugged straight into the diverter valve. I don't know how I missed it. I don't know why it would still be that connector. I fixed it several days ago, and it all works great now.

 

[CorvairGeek]

Glad you got things straightened out.

 

[1987 GMC Jimmy]

Got it off, and I see the regulator in there. I checked to see if there was a BWD or better regulator around here in stock, and there's not. I need the car Thursday, which is why I'm in a slight hurry. I also noticed that the pulley wobbles pretty good when you spin it, kind of like a top that's loosing centrifugal motion, so I'm guessing that's an issue with the shaft or the bearing? I can take it to the guy down the road (Bobby), and he'll rebuild it for like $50. He's done the starter on the same car, the alternator on my dad's truck, the starter on the tractor, and he did an alternator on my dad's plane once, and all of them turned out great.

 

[HotRodPC]

You were right! 15V at idle coming right off the alternator. I don't even want to know what was happening at 2000-3000 RPM. So I guess the voltage regulator on the ole Delcotron is bad. What do I need to do to fix it? No wonder my headlights were brighter than my mom's '02 Suburban's at night. Ahh, I guess you can't win them all. Thanks, HR, for telling me about that. I never would have thought about it.



You were right! Plugged straight into the diverter valve. I don't know how I missed it. I don't know why it would still be that connector. I fixed it several days ago, and it all works great now.

That's good. Mystery solved. I wished I had suggested it much earlier in the thread. I also didn't think nothing about it when I first seen the thread. Then I seen your comment about how many have gone bad, getting only about a week out of them, then I went into a short pause and thought, start at the basics and then go from there, and the first thing that popped in my head was VOLTAGE to high. Sometimes we overthink things and forget the basics.

 

[1987 GMC Jimmy]

I took the alternator to the shop, and he put it on the machine. He told me it was charging correctly, but my voltmeter said 15V at idle right where the battery cable bolts on. He said that I might have a cable or connection issue, but there's no way. I took it to another guy I know, and he went ahead and installed a new regulator for $25. I hope this fixed it. He put it on the machine afterward, and I saw that it was charging normally.

 

[HotRodPC]

I'll be curious to see what voltage reading you get off the alternator after you install it. 13.2 to 13.8 would be optimal.

 

[1987 GMC Jimmy]

I'll be curious to see what voltage reading you get off the alternator after you install it. 13.2 to 13.8 would be optimal.

It's saying 14.6 at idle now. Both at the terminal on the alternator and the battery. I tested my dad's truck the same way, and it was saying 14.6, and the voltmeter on my mom's car is saying about 13.8. I don't know where to really go from here with the alternator. If the voltage is acceptable, I guess I'll have to go through and check the harness pin by pin. I found an ECM voltage diagram for an Olds 307 with CCC, but I imagine it's exactly the same. There's very little literature available for this system. I also noticed that my warning lights aren't working as of a few days ago when I turn the key to on like before. I'd see a choke light, a parking brake light, and a battery light do a little self-test thing. The ECM light is staying on, but I don't have one in it right now so that's why. When I turn it to start, they'll flicker like normal, but the warning lights are dead when the key's on, and the engine's off. Could there be something going on with my ignition switch? I checked the fuses, and they're good, and I watched my choke, and it's working fine. I also checked to see how much voltage the ECM was getting straight off the harness pin. It's saying 10.75 key on, engine off, and it's supposed to be 12, and it's getting 12.1 key on, engine on, and the chart says it's supposed to get 14. My ECM ground is right there sticking up off the top of the floor pan, and I'll double check that, but I think it looks good so I'm not sure...