I’m sorry to hear that you’ve been getting run through the chasing birdies mill...
Sounds like you’ve addressed all the possible ignition problems, and having swapped the injector with no positive results, did you check the injector wiring harness at the connector that plugs into the injector itself for bad wires or contacts ?
(23 year old wiring) insulation hardens, causing the wires to break at the weak points when bent or manipulated.
Arcing a distributor plate happens when there’s nowhere for the spark to go. That’s why you’re not supposed to turn the motor over with a plug wire not properly attached or grounded by holding the plug against a good ground surface when checking spark.
I was thinking the plug wire could be broken and resistance is too high so it’s jumping a gap and sparking in the distributor. But you’ve changed the plug wire, was it with one you KNOW is good and has been tested.
It ran good for a minute after replacing the cap and rotor then burnt the plate again ?
Sounds like spark with nowhere to go...
Beyond that, you may be dealing with a valve train issue, broken spring, bent valve not closing all the way, something mechanical specific to cylinder # 3.
Bad lifters you can generally hear, but a worn out roller bearing or a cam lobe worn down could cause the missing problems you’ve described. But that doesn’t explain the arcing... you could be suffering a dual problem which makes it very difficult to diagnose.
Oh ya, and don’t assume that because a part is new, that it’s working like it’s supposed to, I just went through that myself with a brand new ACDelco EVAP canister purge valve. I kept assuming since it was new it couldn’t be the problem.
I wish I knew more about how the pcm controls ignition, fuel and spark systems, or the test procedures and the proper values testing should produce.
Have you tried posting this on the ISSF forums. More guys with LT1’s over there.