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If your saying number 2 spark plug coil is getting no ground from computer when cranking, I'd have to check wiring connectors on both ends and do continuity test of the ground wire to computer. If everything checks out, check computer.
I suppose you swapped the coil from one cylinder to the next, to see if problem followed the coil?
You do have primary voltage going to coil, correct?
I would be more inclined to think the wiring in the coil pack for that coil may have a problem. Have a shop check your ignition system, before springing for a new pcm. There should be a hot wire to the coil primary wire going to that coil. May have to run continuity tests on the wiring for the coil pack. Or if you could find a used coil pack, and use your good coils on it to try it.
You use the codes & diagnostic manuals, to decide what testing to do,not replace anything at all
Spark plugs seldom go bad or fail to fire,maybe never in your lifetime
I may be the exception, but never replace plug wires. If you have a used vehicle & depend on a repair shop that too many hands abused them, then change them
The idea is to use professional tools such as reference material & an oscilloscope to look into things & spot a problem part,then change it
Now your coil for #4 may have not been the problem A code for a misfire such as a PO304 but not the coil causing it or a different coil spiking the pcm/ecm & giving you all sorts of misleading codes
You could have a bad injector on#4 or a vacuum leak on injector & you go down the trouble chart or tree on your reference material & continue testing
I can write a book but can't diagnose without the vehicle
You either go to Helm.Com and buy the necessary manuals or go to a repair shop to have them do other testing, keep in mind they know not to do the plugs,wires etc you did
There are shops that will throw parts at it, then ask for you authorization to continue, they should be working only on the main problem you go there for,then you build the relationship, if they prove they can solve your complaint
On some chevys the oil pressure sending unit closes the circuit to continue the fuel pump to run after start. In the event of a wreck ,the car stops running thus no oil pressure thus turns off power to the fuel pump .A safety to help prevent fires. When you first start the car, the computer turns on the fuel pump for about 20 seconds just enough time to start and allow the oil pressure sending unit to close the circuit to allow it to continue running. when the car car has NO oil pressure or the sending unit fails ,it will start then shut down..as many times as you try to start. replace the oil pressure sending unit and secure a good conection. Dan
Replace and/or check the the coil packs for continuity associated with the cylinders that are not firing.
Also, check for fuel delivery using a fuel pressure gauge on the rail, and verify that the fuel injectors are firing using a noid tester or a stethoscope on the fuel injector to check that they are clicking.
Try to add starter fluid to the intake manifold through the throttle body to see if it starts that way, signalling a fuel delivery problem if it starts right up.