Wiring Issues

[ikeG]

LLY was towed in here for a no start. Had codes P1226, P0302, and a 1094. Wont build rail while cranking but would fuel smoke some out the tailpipe. Pulled a couple glow plugs to find an injector hung open. Customer agreed to start with a set of injectors. Got them in today, fires right up running great. Soon after set a P1223. Injector 1 output circuit. Which the truck came in with same code for cylinder 2..... It is intermittent, it will run like a top then start missing on cyl 1. What is everyones thoughts? Tommorrow going to test circuits for injector 1, ive already confirmed injector 2 circuits were good prior to recommending new injectors. The pins in the bale connector seem fine.....

 

[2004LB7]

Put a 10 amp fuse in the EDU slot before running it any longer. In case the FICM is going out. You don't want the board to blow a hole in it from an oversized fuse not blowing. Might allow it to be repairable if a capacitor shorts out

I would take the connector off the FICM and prob all the injectors from there. This will test the connection at the injector along with the harness. If you have an LCR meter use that too. Should he around 120 uH for each injector. + Or - about 10 uH seems to be normal but much more then that will throw codes.

 

[ikeG]

Those p1223, etc codes were for the circuit between ficm and ecm based on the diagnostic instructions. But I am going to have to check everything before sending the ficm out.
I just wonder why it switched cylinders after the injector change.

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[2004LB7]

Ah, ok. I didn't look up the code and just went off what you said. You'll need a scope to see the ECM signals to the FICM. I'd check that before condemning the ECM. Could just be a broken wire or bad connection at one of the pins

But if I remember correctly. The FICM doesn't know when the ECM signal is supposed to be there and will happily run with one or possibly two absent signals without throwing a code. So I think it's more about having a signal out of time. Basically two injectors commanded at the same time or having an overlap. So maybe those two injectors have a shorted wire between them and the FICM is trying to guess which one is correct and which one is a false signal. Would explain the fuel smoke exhaust. Commanding the wrong injector will do that.

 

[ikeG]

I only pulled 3 glow plugs, cyl 8 was the one with thw injector hosing fuel. Cyl 2 had the code set upon arrival. Get it running with new injectors, cyl 1 sets the code now.....

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[Ron Nielson]

P1226 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

P1226 Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

www.dtcdecode.com

 

[2004LB7]

P1226 - Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

P1226 Chevrolet Diagnostic Trouble Code (DTC) Definition, Causes and Diagnosis

www.dtcdecode.com

That's pretty much what I was guessing. Nice to see an official bulletin on it

 

[ikeG]

It's those stupid round pins in the ecm connector. I've had trouble with those on 4l60 tcm connectors in the past. I should have some saved here somewhere

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[ikeG]

I could get injectors 1, 3 & 8 to shut down and trip their respective P12xx code by wiggling the injector control wires at the back of the ecm connector. So I replaced those 3 female pins as well as cyl 2, since it had that code set when the truck was hauled in. Problem solved.

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[1FastBrick]

Nice find!