1991 c4
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Heel & Toe
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1991 c4
My 1991 C4 with T.P.I. has absolutely no power coming to the injectors. I've unplugged all of them to check for a signal and the wires are all completely dead. There's a gray wire coming off of the ecm that makes some of the injectors click when I ground a test light and probe the wire. Anybody got any clues as to what I've got going on here?
Thread Starter
Heel & Toe
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I checked both fuses, neither is blown. I also pulled them out to see if there was power coming to the injector slots on the fuse panel and they both have power. Any idea why there's no power at the wire harness to the injectors?
So the ecm could be bad, and not providing a sufficient ground?
So the ecm could be bad, and not providing a sufficient ground?
Last edited by marlonb601; Jun 11, 2011 at 12:00 PM.
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From: Kingman AZ
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I used to own an 87 where the previous owner had to have the passenger side harness replaced due to mice chewing on them. Hard to believe that this would affect all the wires though.
Good luck!
Good luck!
Thread Starter
Heel & Toe
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All of the wires on the harness are in tact, but thanks for your response.
Race Director
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From: Phoenix Arizona
The ECM does not supply power to the injectors. One side is upplied by one fuse, the other by the other fuse. Check again that none of the injectors have power. Check the pink black wire on each injector to a known ground.
Thread Starter
Heel & Toe
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You're absolutely correct!! What I thought was a sufficient source for a ground was not. With a good ground I found that all the injector terminals had power. I also checked the injectors and all but one registered at 16.5 to 16.7 ohms. The injector that didn't read 15.5 ohms. I checked the fuel pressure at the rail and it reads 50 psi when the pump primes. After the pump stops the pressure goes to 25 psi and holds steady. When I try to start up the pressure gauge goes to 50 psi, but the car still won't start. I replaced the oil pressure switch. Could the throttle position sensor be the problem? It did test bad. What are the chances that the VATS system has something to do with the no start state?
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Thread Starter
Heel & Toe
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I have squirted gas directly into the throttle body and the car starts, but once the gas burns off it dies.
Race Director
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From: Phoenix Arizona
Do you have 12v on your ecm fuse? Do you have a check engine(service engine soon) light when you juston the ignition? Do you have 12v to the oil pressure switch - orange wire? (D17 on the computer)
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Heel & Toe
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I check all of that and log on later with the info. Thanks for your help.
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Heel & Toe
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Jump terminals A and B on the ALDL and turn the key on. The check engine light should flash 3 "12" codes.....flash pause flash flash. Post if that is happening.
Now....check continuity between the injector wires where they go into the ECM and the injectors themselves with the harness unplugged from the ECM. Tell me what you have. Your '91 is batch fire....ie....all left injectors fire at the same time, and all right injectors fire at the same time.
If you have power to the injectors, continuity from the ECM to the injectors, but they aren't firing, either the ECM isn't receiving a crank signal from the distributor, or the ECM itself is faulty.
Happy hunting....post what you find out.
Now....check continuity between the injector wires where they go into the ECM and the injectors themselves with the harness unplugged from the ECM. Tell me what you have. Your '91 is batch fire....ie....all left injectors fire at the same time, and all right injectors fire at the same time.
If you have power to the injectors, continuity from the ECM to the injectors, but they aren't firing, either the ECM isn't receiving a crank signal from the distributor, or the ECM itself is faulty.
Happy hunting....post what you find out.
Race Director
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From: El Paso Texas
VATS would likely cause a no-crank condition along with disabling fuel trim.
Thread Starter
Heel & Toe
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Jump terminals A and B on the ALDL and turn the key on. The check engine light should flash 3 "12" codes.....flash pause flash flash. Post if that is happening.
Now....check continuity between the injector wires where they go into the ECM and the injectors themselves with the harness unplugged from the ECM. Tell me what you have. Your '91 is batch fire....ie....all left injectors fire at the same time, and all right injectors fire at the same time.
If you have power to the injectors, continuity from the ECM to the injectors, but they aren't firing, either the ECM isn't receiving a crank signal from the distributor, or the ECM itself is faulty.
Happy hunting....post what you find out.
Now....check continuity between the injector wires where they go into the ECM and the injectors themselves with the harness unplugged from the ECM. Tell me what you have. Your '91 is batch fire....ie....all left injectors fire at the same time, and all right injectors fire at the same time.
If you have power to the injectors, continuity from the ECM to the injectors, but they aren't firing, either the ECM isn't receiving a crank signal from the distributor, or the ECM itself is faulty.
Happy hunting....post what you find out.
Last edited by marlonb601; Jun 27, 2011 at 05:23 PM. Reason: New Info to add
Le Mans Master
Joined: Oct 2008
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From: Houston Texas
Put one end off the lead on the injector side of the ground and the other of the ECM side while unplugged. Put the OHM meeter on the Simbold that looks like a Jet airplane LOL.
Here is a video.
Here is a video.
Thread Starter
Heel & Toe
Joined: Dec 2010
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Thanks for the tutorial and the video!!! I feel a lil smarter now! LOL!!! Again. Thank you.
