Electrical (ECM?) Issues
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Electrical (ECM?) Issues
Recently I've encountered some electrical issues with my car. Frequently, I'll turn the key to on, but my C68 screen will just show 3 horizontal dashes instead of the temperature, and the climate control blower will turn on high. Tonight I took it for a test drive and noticed that the dash LCD intermittently flashes "SYS."
I know low voltage can cause the latter, but my battery tests at 12.9v and somewhere around 15v with the engine running.
My only thoughts are that I have a bad ECM ground or possibly my ECM is going out?
I've been trying to connect to my ECM via a bluetooth adapter plugged into the ALDL port, but have getting lots of errors and garbled data. I think I may not have the correct ADX file, but is it possible that whatever's causing my other problems is causing ALDL datastreams to be corrupted?
My car is a 1990 6-speed coupe, ECM number 1227727.
I know low voltage can cause the latter, but my battery tests at 12.9v and somewhere around 15v with the engine running.
My only thoughts are that I have a bad ECM ground or possibly my ECM is going out?
I've been trying to connect to my ECM via a bluetooth adapter plugged into the ALDL port, but have getting lots of errors and garbled data. I think I may not have the correct ADX file, but is it possible that whatever's causing my other problems is causing ALDL datastreams to be corrupted?
My car is a 1990 6-speed coupe, ECM number 1227727.
Safety Car
Joined: Nov 2008
Posts: 4,328
Likes: 15
From: Jacksonville FL
I know nothing about your issue except wouldnt think the ALDL port would be a good place to "connect" anything except test equipment. Ive never heard of it but that dont mean anything, lol.
The C68 issue may just be a bad ground. Whether that comes from the ECM I dont know. Doesnt the C68 have its own ECM unit?
Hopefully someone that can truly help will chime in.
Good luck!
The C68 issue may just be a bad ground. Whether that comes from the ECM I dont know. Doesnt the C68 have its own ECM unit?
Hopefully someone that can truly help will chime in.
Good luck!
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
I know nothing about your issue except wouldnt think the ALDL port would be a good place to "connect" anything except test equipment. Ive never heard of it but that dont mean anything, lol.
The C68 issue may just be a bad ground. Whether that comes from the ECM I dont know. Doesnt the C68 have its own ECM unit?
Hopefully someone that can truly help will chime in.
Good luck!
The C68 issue may just be a bad ground. Whether that comes from the ECM I dont know. Doesnt the C68 have its own ECM unit?
Hopefully someone that can truly help will chime in.
Good luck!
Diagnosis tools to read ECM data, basically code readers, connect at the ALDL port.
I believe the C68 does have its own computer module, but I thought it might somehow be connected to the main ECM.
When I replace my engine I guess I'll just have to clean every ground I can find.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
Most of the engine grounds connect to G104, which I believe is attached to a bell housing bolt on the driver's side on your year. I know it was in 1989. Mine is on the side of the block above the oil filter, so sometime between 1986 and 1989 it got moved.
The dash grounds connect to G201, which is on the driver's side hinge pillar just above where the round dash brace attaches. You will have to take off the frame rail cover to see it.
The dash grounds connect to G201, which is on the driver's side hinge pillar just above where the round dash brace attaches. You will have to take off the frame rail cover to see it.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Most of the engine grounds connect to G104, which I believe is attached to a bell housing bolt on the driver's side on your year. I know it was in 1989. Mine is on the side of the block above the oil filter, so sometime between 1986 and 1989 it got moved.
The dash grounds connect to G201, which is on the driver's side hinge pillar just above where the round dash brace attaches. You will have to take off the frame rail cover to see it.
The dash grounds connect to G201, which is on the driver's side hinge pillar just above where the round dash brace attaches. You will have to take off the frame rail cover to see it.
On a hunch, I tested the alternator tonight. Before starting I had 12.4v, then it jumped to 14.5 or so when I started the engine. However, not long after I started it, my low battery light came on, the charger said I had a bad alternator, and the current across the terminals was back to 12.4v.
What can cause an alternator to stop working intermittently? Is it something that I can fix without replacing the alternator?
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
My alternator would sometimes go to zero output. I could see it on the voltmeter and the red light would come on. I hit the alternator (gently) with a hammer and the voltage jumped up. I took it apart and didn't see anything obvious. I cleaned it up and put it back together and it's been fine for several years since then. Obviously a loose connection in there somewhere.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
My alternator would sometimes go to zero output. I could see it on the voltmeter and the red light would come on. I hit the alternator (gently) with a hammer and the voltage jumped up. I took it apart and didn't see anything obvious. I cleaned it up and put it back together and it's been fine for several years since then. Obviously a loose connection in there somewhere.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
My alternator would sometimes go to zero output. I could see it on the voltmeter and the red light would come on. I hit the alternator (gently) with a hammer and the voltage jumped up. I took it apart and didn't see anything obvious. I cleaned it up and put it back together and it's been fine for several years since then. Obviously a loose connection in there somewhere.
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Melting Slicks
Joined: Oct 2000
Posts: 2,158
Likes: 9
From: N.E. WA
My alternator would sometimes go to zero output. I could see it on the voltmeter and the red light would come on. I hit the alternator (gently) with a hammer and the voltage jumped up. I took it apart and didn't see anything obvious. I cleaned it up and put it back together and it's been fine for several years since then. Obviously a loose connection in there somewhere.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
Well, the problem is back. My sister killed it when I was teaching her to drive a stick, and I think that shook something loose, because the battery light immediately came on and the voltage needle dropped.
While trying to diagnose the problem, I wondered if there could be a bad connection somewhere, so I broke out the multimeter. Voltage at the battery was 12.1v, about what I expected, but I got an entirely different reading at the alternator.
Testing from the alternator positive wire to the battery ground, I got a reading of 17.6v! Is there some sort of battery protection circuit in the wiring that cuts off alternator current if the voltage gets too high? Or is it possible that there's a short, so the regulator keeps amping up voltage to compensate?
EDIT: I started it to do some more testing with the DMM and it seems the problem fixed itself. No battery light, no abnormal voltage gauge reading, and 15.15v from the alternator. Perhaps the problem is caused by something overheating?
I just took it for a drive, and now the idle's all messed up. It was already a little high from a vacuum leak, but now it's about 500 RPM higher and it is hunting a bit. I have no idea how that's connected to my alternator.
While trying to diagnose the problem, I wondered if there could be a bad connection somewhere, so I broke out the multimeter. Voltage at the battery was 12.1v, about what I expected, but I got an entirely different reading at the alternator.
Testing from the alternator positive wire to the battery ground, I got a reading of 17.6v! Is there some sort of battery protection circuit in the wiring that cuts off alternator current if the voltage gets too high? Or is it possible that there's a short, so the regulator keeps amping up voltage to compensate?
EDIT: I started it to do some more testing with the DMM and it seems the problem fixed itself. No battery light, no abnormal voltage gauge reading, and 15.15v from the alternator. Perhaps the problem is caused by something overheating?
I just took it for a drive, and now the idle's all messed up. It was already a little high from a vacuum leak, but now it's about 500 RPM higher and it is hunting a bit. I have no idea how that's connected to my alternator.
Last edited by C4ProjectCar; Dec 22, 2014 at 09:26 PM.
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
While trying to diagnose the problem, I wondered if there could be a bad connection somewhere, so I broke out the multimeter. Voltage at the battery was 12.1v, about what I expected, but I got an entirely different reading at the alternator.
Testing from the alternator positive wire to the battery ground, I got a reading of 17.6v! Is there some sort of battery protection circuit in the wiring that cuts off alternator current if the voltage gets too high? Or is it possible that there's a short, so the regulator keeps amping up voltage to compensate?
Testing from the alternator positive wire to the battery ground, I got a reading of 17.6v! Is there some sort of battery protection circuit in the wiring that cuts off alternator current if the voltage gets too high? Or is it possible that there's a short, so the regulator keeps amping up voltage to compensate?
The alternator has a voltage regulator circuit inside it that determines what voltage comes out. It also limits the current so nothing burns up.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
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From: Lynchburg, VA
The wire between the alternator and the battery has a fusible link in it to protect the connection. The fusible link is on the end that attaches to the "jumper post" behind the battery. You might have a bad connection there. The voltage at the alternator should be the same as the voltage at the battery (within a few tenths of a volt). If not then there's a problem with the wiring between them.
The alternator has a voltage regulator circuit inside it that determines what voltage comes out. It also limits the current so nothing burns up.
The alternator has a voltage regulator circuit inside it that determines what voltage comes out. It also limits the current so nothing burns up.
Why would the alternator voltage have been at 17v though? Does the ECM crank up alternator voltage if the battery voltage drops?
Race Director
Joined: Apr 2002
Posts: 10,036
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From: Anaheim CA
The ECM has no control over the alternator voltage. It's all done inside the alternator by the voltage regulator.
Melting Slicks
Joined: Jun 1999
Posts: 2,931
Likes: 127
From: Ashland Alabama
Hmm, I replaced most of the fusible links there when I first bought it (PO shorted a jumper cable to the frame) so that seems likely. I either didn't put it back together right or I missed one of the fusible links. Guess I'll take the battery out and see what I find. Thanks for the tip.
Why would the alternator voltage have been at 17v though? Does the ECM crank up alternator voltage if the battery voltage drops?
Why would the alternator voltage have been at 17v though? Does the ECM crank up alternator voltage if the battery voltage drops?
Simple test is when its not "working" use one of the leads on a set of jumper cables to go from the ground terminal on the battery to the alternator case. If it suddenly goes back to charging then you've found your problem.
If that is the problem then check the ground wires to the motor.
Thread Starter
Drifting
Joined: Jul 2014
Posts: 1,426
Likes: 46
From: Lynchburg, VA
You probably didn't have a good reference ground for your meter and picked up some extra voltage. To do it right you need a solid connection to some point that you call "ground". There will be slight voltage differences between that point and anything else connected to it because of the resistance of the metal in the block, frame, etc. I use the negative battery terminal.
The ECM has no control over the alternator voltage. It's all done inside the alternator by the voltage regulator.
The ECM has no control over the alternator voltage. It's all done inside the alternator by the voltage regulator.
Id check the ground to the block. 99% of the time if the alternator isn't bad and just stops charging randomly its a ground problem. Ive seen it so bad before on one vehicle the volts would drop on the gauge just by turning the wheel to make a turn.
Simple test is when its not "working" use one of the leads on a set of jumper cables to go from the ground terminal on the battery to the alternator case. If it suddenly goes back to charging then you've found your problem.
If that is the problem then check the ground wires to the motor.
Simple test is when its not "working" use one of the leads on a set of jumper cables to go from the ground terminal on the battery to the alternator case. If it suddenly goes back to charging then you've found your problem.
If that is the problem then check the ground wires to the motor.