12200411 PCM swap for 1996 to 2000 GMT400 trucks

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Douglas1300

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I have continuity from 26Red pin to ICM white wire, ICM WHT/Black to Coil, and ign power with key on to both, also good ground to ICM. so the only thing left is what signal to test for and how from PCM. if that's good, then what signal does the ICM send to the coil and how to test that?
 

AK49BWL

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I can't find anything wrong with your tune file while comparing it to mine.. Other than the differences between a 350 and 383 of course. I'd look into the hardware. The only signal from the ICM to the coil should be the spark trigger itself, not sure if there's any way to test that other than continuity - Pin D on the ICM goes to Pin C on the coil. I'm not sure what the PCM would send to the ICM to be honest..

In HPT Scanner, do you get all the various sensor readings? MAP, MAF, temp sensors, EGR, etc? Current firing cylinder? I'd enable the Current Firing Cylinder PID and see if it changes at all when you try to start the truck.
 

AK49BWL

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The only way to truly know would be to swap it out to a known-good working PCM afaik... personally? I would go through and replace everything ignition-related before I went so far as to replace a PCM I've already used a $100 note on for HPT credits, which would then require another $100 to license. ICM/Coil/Dist Rotor/Cap/Plugs/Wires, pretty sure still ends up under $200 :D Oh and the distributor caps LOVE to go bad on these so that might be a worthwhile replacement anyway. I don't think it was mentioned, how are you checking for spark?
 

Douglas1300

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The only way to truly know would be to swap it out to a known-good working PCM afaik... personally? I would go through and replace everything ignition-related before I went so far as to replace a PCM I've already used a $100 note on for HPT credits, which would then require another $100 to license. ICM/Coil/Dist Rotor/Cap/Plugs/Wires, pretty sure still ends up under $200 :D Oh and the distributor caps LOVE to go bad on these so that might be a worthwhile replacement anyway. I don't think it was mentioned, how are you checking for spark?

That is all brand new. except for the ICM I replaced them all as a tune up for my journey from SC to WA. all A/C Delco from GM except for the distributor I replace with the stock MSD replacement as it has the billet aluminum body and my original gm Distributor was plastic and had cracked.
 

AK49BWL

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Gotcha... Well, if not the ICM, then yeah, PCM would be the most likely culprit.
 

Douglas1300

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checked for spark with a new sprk plug grounded in #1 plug. and then tested coil output to ground with test light to check for the spark jump.
 
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