Injectors not firing
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Intermediate
Joined: Sep 2025
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Injectors not firing
Hey guys this is my first post here and have found a lot of help in searching around prior to this. I recently picked up a 92 project, wouldnt even crank over when i picked it up. Got a new key made up for it and got it cranking, ooti was bad and got that replaced along with the ignition coil and spark plug wires. Now I'm down to fuel.
Fuel pump is working and I have fuel pressure at the rail. But the injectors are not firing, confirmed with a noid light.
So far the fusable kinks were pretty corroded so I got those cleaned up as well as the 2 grounds under the battery tray, next is to hit the ground locations on the bell housing.
It seems the wiring harness has been messed with in the past, wires that don't seem to be factory on the green plug in the ecm.
Would anyone be able to tell me which plug or plugs at the ecm have the 12v supply and ground? I found somewhere if I remember correctly that the black with white tracer was the ground for the fuel injectors (fuses are not blown on a side note). Or does anyone have any suggestions on what I should be looking in to next?
Any help would be greatly appreciated.
Fuel pump is working and I have fuel pressure at the rail. But the injectors are not firing, confirmed with a noid light.
So far the fusable kinks were pretty corroded so I got those cleaned up as well as the 2 grounds under the battery tray, next is to hit the ground locations on the bell housing.
It seems the wiring harness has been messed with in the past, wires that don't seem to be factory on the green plug in the ecm.
Would anyone be able to tell me which plug or plugs at the ecm have the 12v supply and ground? I found somewhere if I remember correctly that the black with white tracer was the ground for the fuel injectors (fuses are not blown on a side note). Or does anyone have any suggestions on what I should be looking in to next?
Any help would be greatly appreciated.
Safety Car
Joined: Aug 2009
Posts: 3,751
Likes: 276
From: Melbourne, Victoria, Australia
Hey guys this is my first post here and have found a lot of help in searching around prior to this. I recently picked up a 92 project, wouldnt even crank over when i picked it up. Got a new key made up for it and got it cranking, ooti was bad and got that replaced along with the ignition coil and spark plug wires. Now I'm down to fuel.
Fuel pump is working and I have fuel pressure at the rail. But the injectors are not firing, confirmed with a noid light.
So far the fusable kinks were pretty corroded so I got those cleaned up as well as the 2 grounds under the battery tray, next is to hit the ground locations on the bell housing.
It seems the wiring harness has been messed with in the past, wires that don't seem to be factory on the green plug in the ecm.
Would anyone be able to tell me which plug or plugs at the ecm have the 12v supply and ground? I found somewhere if I remember correctly that the black with white tracer was the ground for the fuel injectors (fuses are not blown on a side note). Or does anyone have any suggestions on what I should be looking in to next?
Any help would be greatly appreciated.
Fuel pump is working and I have fuel pressure at the rail. But the injectors are not firing, confirmed with a noid light.
So far the fusable kinks were pretty corroded so I got those cleaned up as well as the 2 grounds under the battery tray, next is to hit the ground locations on the bell housing.
It seems the wiring harness has been messed with in the past, wires that don't seem to be factory on the green plug in the ecm.
Would anyone be able to tell me which plug or plugs at the ecm have the 12v supply and ground? I found somewhere if I remember correctly that the black with white tracer was the ground for the fuel injectors (fuses are not blown on a side note). Or does anyone have any suggestions on what I should be looking in to next?
Any help would be greatly appreciated.
You should have 12 volts to injectors with ignition on and cranking, assuming the vehicle anti theft system (within the central command module) is happy with ignition key resistance. The ECM drives the injectors by grounding them "batch firing" one bank at a time.
The ZR1 went sequential not sure what year that became normal to go from batch firing one bank of injectors at a time to sequential in other years .... 🤔
Hopefully someone can post a pic fro. their 92 workshop manual, as they went optispark will be differences from anything in my 91 manual won't relate to your 92 ..
Good luck 👍
Thread Starter
Intermediate
Joined: Sep 2025
Posts: 25
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I am only familiar with early C4's and my 91, the fuel injectors got 12 volts from the injector fuse via ignition and later the ccm vats would be involved with enabling fuel pump and Ignition.
You should have 12 volts to injectors with ignition on and cranking, assuming the vehicle anti theft system (within the central command module) is happy with ignition key resistance. The ECM drives the injectors by grounding them "batch firing" one bank at a time.
The ZR1 went sequential not sure what year that became normal to go from batch firing one bank of injectors at a time to sequential in other years .... 🤔
Hopefully someone can post a pic fro. their 92 workshop manual, as they went optispark will be differences from anything in my 91 manual won't relate to your 92 ..
Good luck 👍
You should have 12 volts to injectors with ignition on and cranking, assuming the vehicle anti theft system (within the central command module) is happy with ignition key resistance. The ECM drives the injectors by grounding them "batch firing" one bank at a time.
The ZR1 went sequential not sure what year that became normal to go from batch firing one bank of injectors at a time to sequential in other years .... 🤔
Hopefully someone can post a pic fro. their 92 workshop manual, as they went optispark will be differences from anything in my 91 manual won't relate to your 92 ..
Good luck 👍
Thread Starter
Intermediate
Joined: Sep 2025
Posts: 25
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Thankyou! I completely missed the 10 and 11 at the bottom there. So I should have 12v across those terminals?
I've continued my search from this forum and found some old posts that say I should have 12v on each pin on the injector plug to ground, I'm only getting that 12v from the pink wire from the driver side and green from passenger.
I've continued my search from this forum and found some old posts that say I should have 12v on each pin on the injector plug to ground, I'm only getting that 12v from the pink wire from the driver side and green from passenger.
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Le Mans Master
Joined: May 2004
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I am only familiar with early C4's and my 91, the fuel injectors got 12 volts from the injector fuse via ignition and later the ccm vats would be involved with enabling fuel pump and Ignition.
You should have 12 volts to injectors with ignition on and cranking, assuming the vehicle anti theft system (within the central command module) is happy with ignition key resistance. The ECM drives the injectors by grounding them "batch firing" one bank at a time.
The ZR1 went sequential not sure what year that became normal to go from batch firing one bank of injectors at a time to sequential in other years .... 🤔
Hopefully someone can post a pic fro. their 92 workshop manual, as they went optispark will be differences from anything in my 91 manual won't relate to your 92 ..
Good luck 👍
You should have 12 volts to injectors with ignition on and cranking, assuming the vehicle anti theft system (within the central command module) is happy with ignition key resistance. The ECM drives the injectors by grounding them "batch firing" one bank at a time.
The ZR1 went sequential not sure what year that became normal to go from batch firing one bank of injectors at a time to sequential in other years .... 🤔
Hopefully someone can post a pic fro. their 92 workshop manual, as they went optispark will be differences from anything in my 91 manual won't relate to your 92 ..
Good luck 👍
I believe that was 1994 for the pushrod Vettes going to sequential.
Drifting
Joined: Oct 2004
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From: Hawaii
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The opti provides the crank position signal to the PCM. Without that, the PCM won't fire the injectors. A lot of new optis seem to come DOA, or you may have a problem in the harness from the opti to the PCM. You'll need to test for that opti signal at the PCM input to see if you're getting one.
Thread Starter
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The opti provides the crank position signal to the PCM. Without that, the PCM won't fire the injectors. A lot of new optis seem to come DOA, or you may have a problem in the harness from the opti to the PCM. You'll need to test for that opti signal at the PCM input to see if you're getting one.
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Got back to it, found out there was one ignition control module left out of any stores within 100 miles so I figured I would pick it up. Swapped that in and coincidentally? My info screen came back on and was able to pull some codes.
Got a c41, h41 and an err. Not sure what to do about that yet.
In the meantime i tested the connector at the igm plug, got 12v off of A and D and from what I understand I should have 12v and under 5v. The ground is good. Need to figure that one out next
Last discrepancy would be at the opti, the wires are landed correctly A-D on the connector, but if I'm looking at the picture/diagram in the service manual, how my connector lands is reversed. A is where D~ and so on, per the photo of the diagram.
Hunting all the gremlins continues.
Got a c41, h41 and an err. Not sure what to do about that yet.
In the meantime i tested the connector at the igm plug, got 12v off of A and D and from what I understand I should have 12v and under 5v. The ground is good. Need to figure that one out next
Last discrepancy would be at the opti, the wires are landed correctly A-D on the connector, but if I'm looking at the picture/diagram in the service manual, how my connector lands is reversed. A is where D~ and so on, per the photo of the diagram.
Hunting all the gremlins continues.
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Intermediate
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Going to keep posting in case anyone else has the same problems. I sent my ecm out to SIA electronics and they had to re flow the board. Got it back in the car and still no injector pulse. I guess next I'm getting to the ccm and testing the data wire that connects all the computers.
Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
Thread Starter
Intermediate
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The security light goes off when the engine is cranking but I'm not remembering if it stays off when the key drops back to run or accessory.
Thread Starter
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I will definitely look in to that as well. 😂😂 Nice to meet you over here! I was just about to respond to your reply on my other post that I ordered another memcal and I'll see how it goes and get back to you lol
Melting Slicks
Joined: Nov 2016
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From: So Cal
2023 C4 of the Year Finalist - Unmodified
"VATS" does not disable spark or the fuel pump. Only the injectors and starter. It should fire on starter fluid even with an active VATS.
The SECURITY light should never be ON with the key in RUN. If it is on, it is indicating a VATS inhibit, or if the engine is running a problem with the key resistance circuit. (Warning the driver that it may not start the next time.)
It is possible that a previous owner bypassed the starter relay. If the factory alarm is functional, there is a way to test if the starter relay is still active:
Unless the Fuel Enable requirement has been eliminated with a custom chip/tune, the really easy thing to do and remember is that the SECURITY light should never be ON with the key in RUN. If it is, there will be no injector pulse.
The SECURITY light should never be ON with the key in RUN. If it is on, it is indicating a VATS inhibit, or if the engine is running a problem with the key resistance circuit. (Warning the driver that it may not start the next time.)
It is possible that a previous owner bypassed the starter relay. If the factory alarm is functional, there is a way to test if the starter relay is still active:
- Get in the car.
- Have the ignition key in your hand, not in the lock.
- Lock the doors with the power door locks. The SECURITY light should go solid-on.
- Close the door. SECURITY light should go off after a few seconds. The alarm is armed.
- Insert the key in the ignition, the horn should start honking. If it doesn't, turn on the park lights as they are also a 'wake-up' that will set off the alarm.
- With the horn honking, attempt to start/crank the engine. (It shouldn't crank because the CCM also disables the starter if the alarm is set off.) If it cranks, the relay is bypassed.
- Get out of the car and disarm the alarm with the door key.
Unless the Fuel Enable requirement has been eliminated with a custom chip/tune, the really easy thing to do and remember is that the SECURITY light should never be ON with the key in RUN. If it is, there will be no injector pulse.
Last edited by IHBD; Nov 14, 2025 at 08:15 PM.