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Short back story: 2002 Z28 M6 with 67k. About a month ago, my headlights and dash lights started pulsing while my voltage fluctuated about the width of the needle in the factory cluster. Didn't get to a point of causing issues but depending on RPMs, it would range from about 12V to 17V. Battery is an Optima red top with an 11/18 date. When getting new tires mounted in 12/19, Firestone told me the battery was bad...can't remember specifics. Took it to Advance yesterday, they said it "was good but needed a charge because it only showed 12.1V, not 12.3V." Oreilly's said it "needed a charge and they couldn't tell if it was good or bad."
So the other morning on my drive to work, I got a P0308 Cyl 8 misfire and the P0200 injector circuit malfunction. Both injector fuses are fine, all injectors on Bank 2 show 13.6 ohms. Battery showed 11.97V, while #8 injector had 11.47V. Tested #8 with a noid light, which stayed lit constantly with the ignition on and the engine running. I'm about to start tracing wires today but I'm wondering if it's more likely the PCM. If I had a bad ground somewhere, could the issue only be isolated to the #8 injector? Does anyone have any thoughts? I've seen similar issues on here, but many went unresolved or at least were left with no ending. I appreciate anyone's help.
ETA: Since clearing the codes a couple times and working through diagnosing, it comes back with a P0300 and not the P0308. But I feel like the issue is still #8. Unplugging #8 injector doesn't affect the misfire, while unplugging any of the others does make it noticeably worse.
Make sure all wires connected to the ground bolt on the rear of the driver side head are secure and clamped down. Make sure you have a good ground at the battery and the post just aft of the battery on the inner fender passenger side. Make sure you have a good ground at the alternator.
Check the pins on the male side of each connection for each injector and coil. I had a similar issue and finally replaced the coil harness on each side. After 20 years the wires really get brittle and start to crack.
You can isolate which cylinder is misfiring and/or not getting fuel by shooting a temp gun at each exhaust pipe (assuming you have headers). If it's not firing at idle the pipe will be cold compared to the other pipes on each side. Obviously you want to make sure you have good plug wires where one didn't get broken when pulling the boots off of the spark plug. When reconnecting make sure to apply dielectric or silicone to each boot. Makes it a lot easier to remove the next time.
Figured it out. After tracing the wire from the #8 injector to the PCM, I found where the harness was rubbing against the lip on the firewall right above the PCM where the wires come out of the wire loom. You can actually see where it looks like it was shorting out on it. Needless to say, it was the blue/white wire coming from Cyl 8 injector. Quick cut, solder and heat shrink and it was good as new. I plan to get some small vacuum tubing, cut a slit in it and slide it onto that lip to prevent it from rubbing on it again. Glad it was a quick, cheap fix. Thanks for the input guys!
03-28-2021, 08:45 AM
P0200, P0300 & P0308? Bad battery, ground or PCM? 
