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Discussion Starter · #1 ·
Hello, I am having issues with my truck and I need help. I have a 1999 GMC Sonoma and it is misfiring bad. I was reduced to a part swapper and spent loads of $$ like an idiot to no avail. The truck has new spark plugs & wires, new injectors, injector harness and fuel filter, and I also put on a new valve cover & intake gasket just because they were off and who knows how long its been since they were changed if at all. The truck is still having the same issues and I'm back at square one with no progress to show for it. I need guidance on how to go about fixing this truck before I dump more money into it. I understand the P0200 is most definitely causing the P0300 code, so I need to isolate why how I have an open injector circuit. I really need my truck fixed because my poor WS6 has 223k miles on it and doesn't need to be my daily any longer. Please help.

Thank you.
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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What’s your fuel pressure?
 

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Not familiar with S10 injectors access. Are the injectors mounted outside or inside the intake?
The reason I ask is ability to test if they are firing if mounted outside the intake. You can use a digital meter or you can buy a cheap noid light to test if they are firing. It's possible an injector output stage inside the ECM is bad since all injectors and harness are new.
 

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Discussion Starter · #5 ·
Not familiar with S10 injectors access. Are the injectors mounted outside or inside the intake?
The reason I ask is ability to test if they are firing if mounted outside the intake. You can use a digital meter or you can buy a cheap noid light to test if they are firing. It's possible an injector output stage inside the ECM is bad since all injectors and harness are new.
The injectors are mounted outside the intake. I used a test light since I don't have a noid light. I put both ends of the test light on each little pin of the "ev1" connector or whatever it's called and had my gf turn the key. Each connector was giving me light when tested. I saw that I should check for a bad ground by putting my alligator clip onto the positive side of the battery and putting the test light lead onto the ground of each connector, but I didn't think it was necessary when I had already used my test light essentially as a noid light. Tell me if I'm wrong on that one.

Thanks.
 

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The injectors are mounted outside the intake. I used a test light since I don't have a noid light. I put both ends of the test light on each little pin of the "ev1" connector or whatever it's called and had my gf turn the key. Each connector was giving me light when tested. I saw that I should check for a bad ground by putting my alligator clip onto the positive side of the battery and putting the test light lead onto the ground of each connector, but I didn't think it was necessary when I had already used my test light essentially as a noid light. Tell me if I'm wrong on that one.

Thanks.
Did your gf turn the key to ON only or did she start the truck? Gave you a flashing light or solid light with test light pins both connected to the injector connector?

With ignition key on, there should be 12V only at one pin of injector connector. Other pin is not connected to ground yet. Only time other pin is pulsed to ground by ECM is when cranking. So putting test light alligator clip to positive side of battery and the other to ground is not necessary since there is no path to ground yet with just ignition key to ON.

I just got home from a 14 hour drive, and I will have to crash to bed soon.
 

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Discussion Starter · #7 ·
Did your gf turn the key to ON only or did she start the truck? Gave you a flashing light or solid light with test light pins both connected to the injector connector?

With ignition key on, there should be 12V only at one pin of injector connector. Other pin is not connected to ground yet. Only time other pin is pulsed to ground by ECM is when cranking. So putting test light alligator clip to positive side of battery and the other to ground is not necessary since there is no path to ground yet with just ignition key to ON.

I just got home from a 14 hour drive, and I will have to crash to bed soon.
She turned the key fully and cranked the engine and my test light pulsed on each injector connector.
Thanks for your help, I'll keep this thread updated but I too have work eating up most of my time and I really only get to work on the truck on weekends.
 

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If all injectors pulsed while cranking, then the ECM is providing the ground pulse. Question is, was it consistent?
Why the P0200 then?

Possibilities:
Open or shorted injector - No, you said all injectors are new.
Injector low internal resistance (basically an injector that works, but is out of specs) No, you said all injectors are new. (verify all injector resistance vs specs)
Grounded driver circuit - No, test light pulsed on all injectors
Open driver circuit - No, all injectors pulsed.
Driver circuit shorted to voltage - No, all injectors pulsed.
Wiring harness intermittently shorting against underhood components - No, harness is new.

Verify your fuel pressure first.
Then perform compression test.
 

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Discussion Starter · #9 ·
If all injectors pulsed while cranking, then the ECM is providing the ground pulse. Question is, was it consistent?
Why the P0200 then?

Possibilities:
Open or shorted injector - No, you said all injectors are new.
Injector low internal resistance (basically an injector that works, but is out of specs) No, you said all injectors are new. (verify all injector resistance vs specs)
Grounded driver circuit - No, test light pulsed on all injectors
Open driver circuit - No, all injectors pulsed.
Driver circuit shorted to voltage - No, all injectors pulsed.
Wiring harness intermittently shorting against underhood components - No, harness is new.

Verify your fuel pressure first.
Then perform compression test.
I have some information I just wanted to add to this thread. My brother came down to help me diagnose and pin point the issue. After numerous tests of looking at graphs and live data with his fancy snap-on diagnostic scanner and checking the integrity of the wiring harness all the way from the injector connectors, to the fuel pump relay, all the way to the pcm, he found that the pcm ground terminal for injectors 3 & 4 is bad. Injectors 1 & 2 are on a separate bank with the blue connector, and 3 & 4 are on the black side. Going to get a new pcm and get it programmed and I'll report back my progress.
 

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Great!
Have you explored sending the pcm for testing and repair to ecu repair shops online? Cheaper than a new one.
 

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Discussion Starter · #11 ·
Great!
Have you explored sending the pcm for testing and repair to ecu repair shops online? Cheaper than a new one.
No I was not aware that was an option. I ordered one off ebay, not sure of the integrity of the pcm (if its a bad idea or not). I provided the vin for them to program the pcm properly and assumed this was the route I should take. Any thoughts on these ebay dealers programming pcm's?
 

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You already bought it so it's ok. Just make sure they have a warranty.

It was just a suggestion to get it tested and repaired because you know the pcm came from your truck and the injector final stage transistors for cyl 3 and 4 maybe just need to be replaced.
 

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Discussion Starter · #13 ·
You already bought it so it's ok. Just make sure they have a warranty.

It was just a suggestion to get it tested and repaired because you know the pcm came from your truck and the injector final stage transistors for cyl 3 and 4 maybe just need to be replaced.
It was the PCM. Got my new PCM in and the truck fired up fine. Thanks.
 

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I have some information I just wanted to add to this thread. My brother came down to help me diagnose and pin point the issue. After numerous tests of looking at graphs and live data with his fancy snap-on diagnostic scanner and checking the integrity of the wiring harness all the way from the injector connectors, to the fuel pump relay, all the way to the pcm, he found that the pcm ground terminal for injectors 3 & 4 is bad. Injectors 1 & 2 are on a separate bank with the blue connector, and 3 & 4 are on the black side. Going to get a new pcm and get it programmed and I'll report back my progress.
Hello
Might be better to have your original part repaired at UpFix - We save you money on rebuilding your failed electronics!

Here is the service link
 
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