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Fun Electrical Problem: Dead ECM?


ns87
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Rather than check / fix each individual wire, have you thought about replacing the wiring harness? That would catch any intermittent shorts or breaks. Just thinking out loud here, but what if a sensor somewhere was shorted internally?

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Rather than check / fix each individual wire, have you thought about replacing the wiring harness? That would catch any intermittent shorts or breaks. Just thinking out loud here, but what if a sensor somewhere was shorted internally?

 

Oh jeez. I think I'd rather shoot myself in the foot than do that. It might work but I certainly don't have that kind of time.

 

long shot, but do you have a spare memcal to try?

 

I was actually running the car off a different memcal on computer #2. 19Cutlass94 has that computer at the moment, maybe I can grab it from him sometime this week.

 

 

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Didn't read it in the thread, but do you have a GM service manual? At least this way you can check all power and ground wires going to the PCM, along with continuity tests for everything else. This definitely seems like a power and/or ground issue for the PCM itself. I have also seen a failing ignition control module fry PCM's. I'll have to think out loud some more.

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Didn't read it in the thread, but do you have a GM service manual? At least this way you can check all power and ground wires going to the PCM, along with continuity tests for everything else. This definitely seems like a power and/or ground issue for the PCM itself. I have also seen a failing ignition control module fry PCM's. I'll have to think out loud some more.

Yes I do. I've actually done that, and 19cutlass94/ I found two bad ground wires. We grounded them properly, but figured those are what killed my ECM. Now my new ECM acts just like my two dead ones.

 

To be honest, if it is the ICM I'd rather sell my car. I have replaced 3 different times since I've owned it. Once "brand new", and twice used. I really don't want to again.

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Ok, I guess you're referring to this?

 

I found two grounds with a resistance of almost negative infinity. Looking at my handy shop manual, they both happen to connect to the Coolant level sensor, MAT sensor (which one is that again and where?), the TPS, MAP, and coolant temperature sensor. Explaining why I've had such random and diverse problems.

 

Here's the question of the day: Where on earth do I go from here? That's a lot of wire

 

We decided to ground the two bad wires ourselves, rather than search through the entire loom. They now OHM at 0 (fixed my meter to read 0 as 0 lol).

 

These two wires are supposed to be grounded by/thru the ECM? Did you splice into the two ground wires and connect them to the chassis, or cut them and connect to ground? If not, how did you repair them?

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also, if you could pass along the pinouts that were bad, I can take a look at my '90 service manual tonight to get an idea. It's been a while since I've dealt with your style ECM so I just need to refresh my memory.

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The two wires ground the ECM/ connect it to all of the sensors. I can take a picture of my service manual tonight.

 

We spliced into the two ground wires and connected them to the chassis ground point. Tested them with the multi-meter and they now read 0ohms instead of the previous infinity.

 

BrianP I really appreciate your interest in this. If I can fix it somewhat easily, then I would love to. The car is parked on a residential road (so no garage), and I am graduating and leaving this town in 2 weeks. Tall order :confused:

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What parts would you need that could help you out with this? I might be able to grab some parts from the junkyard here in binghamton and run up there. They have a 30 day return policy.

 

If you can't get it fixed or sold by the time you graduate, let me know and maybe we could get it down here and then it could be looked at/worked on without worrying about getting a ticket.

 

I had a issue that caused a lot of accessories to not work and caused a clicking from relays and a no start intermittantly and it was caused by a bad battery cable. I fixed that and it cleared up the whole issue. Might be worth it to just try it and see. or I can add it to the list of things to grab if I am at the yard.

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also, if you could pass along the pinouts that were bad, I can take a look at my '90 service manual tonight to get an idea. It's been a while since I've dealt with your style ECM so I just need to refresh my memory.

 

Hey. They were pins C5 and C10. They're both black and known as "sensor ground". I just double checked them right now, and they're both at 0 ohms.

 

Jimmyfloyd: That battery cable is a great idea. The only thing that bothers me, is that the car cranks over. Did yours do that too? Your other offer is great, I will let you know if I need anything

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Just checked the cables. They have 0ohms from negative end to all the grounds. I didn't see where the positive one ran other than the AUX post. Same for that

 

Also, for those playing at home:

 

D17 and C1 are two "battery feeds". With the ignition "ON", and my multi-meter to them, they barely move for the voltage. They go to a 20amp fuse (Fuse is OK), then to the + side of the battery. Shouldn't there be voltage on that?

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Just checked the cables. They have 0ohms from negative end to all the grounds. I didn't see where the positive one ran other than the AUX post. Same for that

 

Also, for those playing at home:

 

D17 and C1 are two "battery feeds". With the ignition "ON", and my multi-meter to them, they barely move for the voltage. They go to a 20amp fuse (Fuse is OK), then to the + side of the battery. Shouldn't there be voltage on that?

 

those feed the ECM 12volts(or whatever the alternator would bump it up to) and are absolutely necessary to run it. if there isn't power there its exactly like removing the ECM fuse, it'll crank but not fire. you might have found another issue.

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Just checked the cables. They have 0ohms from negative end to all the grounds. I didn't see where the positive one ran other than the AUX post. Same for that

 

Also, for those playing at home:

 

D17 and C1 are two "battery feeds". With the ignition "ON", and my multi-meter to them, they barely move for the voltage. They go to a 20amp fuse (Fuse is OK), then to the + side of the battery. Shouldn't there be voltage on that?

 

those feed the ECM 12volts(or whatever the alternator would bump it up to) and are absolutely necessary to run it. if there isn't power there its exactly like removing the ECM fuse, it'll crank but not fire. you might have found another issue.

 

OK! Now, if that is the case.....could I run my own fuse in line wires to the ECM?

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diagrams002.jpg

This is for BrianP. The two "sensor grounds" near the bottom of the page . That's what we grounded ourselves

 

diagrams001.jpg

This is for robertisaar. Those two orange wires are the ones I tested that barely moved my multimeter for voltage reading.

 

Guys I'm excited. We can fix this. I have a feeling one of my harnesses got caught torn somewhere. But I'm not opposed to running new wires if I can get this stupid thing running

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Just, if I were you, I'd just run a jumper, with a fuse in line, across, and see what happens. There should be voltage there anyways, and if there isn't, atleast you'd be fixing one more problem.

 

Just do quick jumpers though, don't do a permanent job, then have to rip it all back apart lol!

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ummmmmm UH OH>>>>>>>>>>>>>>>>>>>> I don't understand the grounding issue.... I don't think you do either.... I think the ECM is grounding the sensor.... It should not be grounded to the BODY!!!!!!!!! You need to do an OHM test with the ground wire at the TPS, MAT sensor, and Coolant level sensors and the two grounds (C5 and C10) I also see that the ground circuits also go to the MAP sensor and coolant Temp sensor... BUT DON'T ACTUALLY GROUND ON THE BODY!

 

 

I will say and suggest what I think is your issue.... the wires on this car run through the c100 connector, IIRC... I bet you have corrosion there...

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I have a computer in the 91 regal I can bring down that I know is good, I just started and drove the car around the other day, and I also believe I have an ICM in the garage, unknown condition on that, I would have to check. 3.1s are all over the place at the yard here so I could pick up just about anything else you would need if you wanted help I could do Sunday, I have a jack and jill party to go to sat. I could maybe even swing it on a weekday, leme know. I also believe I have some spare relays and junk layin around too. I also have a fluke meter I could bring down which may be better than what you are using.

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Just, if I were you, I'd just run a jumper, with a fuse in line, across, and see what happens. There should be voltage there anyways, and if there isn't, atleast you'd be fixing one more problem.

 

Just do quick jumpers though, don't do a permanent job, then have to rip it all back apart lol!

 

Will do! But I will try Ken's suggestion first

 

I will say and suggest what I think is your issue.... the wires on this car run through the c100 connector, IIRC... I bet you have corrosion there...

 

Utoh! I will un-do that ground tomorrow.

 

The C100 is the firewall connector that you unbolt the middle bolt to detach?

 

I have a computer in the 91 regal I can bring down that I know is good, I just started and drove the car around the other day, and I also believe I have an ICM in the garage, unknown condition on that, I would have to check. 3.1s are all over the place at the yard here so I could pick up just about anything else you would need if you wanted help I could do Sunday, I have a jack and jill party to go to sat. I could maybe even swing it on a weekday, leme know. I also believe I have some spare relays and junk layin around too. I also have a fluke meter I could bring down which may be better than what you are using.

 

I'm using a crappy home depot multi-meter with a needle. I will PM you my phone number later tonight or tomorrow and we can plan something. I want to check on these other ideas before I drag anyone to Oneonta.

 

 

 

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ummmmmm UH OH>>>>>>>>>>>>>>>>>>>> I don't understand the grounding issue.... I don't think you do either.... I think the ECM is grounding the sensor.... It should not be grounded to the BODY!!!!!!!!! You need to do an OHM test with the ground wire at the TPS, MAT sensor, and Coolant level sensors and the two grounds (C5 and C10) I also see that the ground circuits also go to the MAP sensor and coolant Temp sensor... BUT DON'T ACTUALLY GROUND ON THE BODY!

 

 

I will say and suggest what I think is your issue.... the wires on this car run through the c100 connector, IIRC... I bet you have corrosion there...

 

I did this before I grounded to the body! So I guess there is no grounding issue afterall. Will undo that body ground tomorrow...

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ummmmmm UH OH>>>>>>>>>>>>>>>>>>>> I don't understand the grounding issue.... I don't think you do either.... I think the ECM is grounding the sensor.... It should not be grounded to the BODY!!!!!!!!! You need to do an OHM test with the ground wire at the TPS, MAT sensor, and Coolant level sensors and the two grounds (C5 and C10) I also see that the ground circuits also go to the MAP sensor and coolant Temp sensor... BUT DON'T ACTUALLY GROUND ON THE BODY!

 

 

I will say and suggest what I think is your issue.... the wires on this car run through the c100 connector, IIRC... I bet you have corrosion there...

 

I did this before I grounded to the body! So I guess there is no grounding issue afterall. Will undo that body ground tomorrow...

 

Yeah, this was one thing I was investigating (whether or not it was a sensor ground) now that I see it, I'll x2 with Ken to undo that splice added to chassis ground.

 

Now that you brought up the power problem at D17 and C1 that's a likely culprit, especially that you also mentioned the flaking out of the fuel pump (gets power on the same circuit)

 

Pull the fuse and check to see which of the two fuse terminals have +12V. Then check for continuity between the OTHER terminal and the D17/C1 pins. Maybe you can confirm if there's a wire problem before the fuse or after. Fuse is definitely good? Didn't blow recently?

 

You can always check the C100 connector, but how (Ken) might this cause the no start/rough running issue?

 

 

 

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You can always check the C100 connector, but how (Ken) might this cause the no start/rough running issue?

voltage drop causing runability issues?

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