The first one failed at around 90K miles, the second around 130000K, the third around 165000 and again this week at 167000K. I've changed spark plugs and plug wires. Always the same cylinder and the frequency has increased. I've checked the ground and the wiring harness for damage. Not sure where to go from here?

  • Welcome to Motor Vehicle Maintenance & Repair! What are you replacing them with? Aftermarket ones or OEM GM ones? And are your numbers correct? Looks like you are adding zeros. I would be highly surprised if you had gone 167 million miles in your truck, especially since the truck is only 6 years old. Instead of replacing it, have you tried moving it to a new location. IE: Exchange the "bad" coil with a known good one? It may be the plug is coming undone or something. Aug 26, 2018 at 12:32
  • Plug wires? I'm surprised that isn't a coil-on-plug motor.
    – 3Dave
    Aug 27, 2018 at 18:00
  • @3Dave it’s coil near plug. To the OP maybe use an attenuator and min/max the coil ground see if there’s some kind of noise when it fires.
    – Ben
    Aug 28, 2018 at 0:51
  • Is water getting under the hood and into the plug wires? Are wires routed near sharp metal edges like heat shields? Arcing to ground will kill those coil packs quickly. Run it in a dark garage with all the lights off and look for sparks to ground. Dec 4, 2019 at 15:18

1 Answer 1


Heat is the big killer. The wires themselves get so hot that their protective coating melts and they short... not completely, but enough for the overall resistance to go down. I mean the wire inside the coil...If you've ever seen a coil of wire (transformer, choke etc.) you will see a colorful wire (usually gold, sometimes other colors like red - but translucent - looks like the wire is copper) that is actually a plastic coating over the wire that has to be scraped off to solder - or melted off.... Could be caused by a) being someplace hotter than usual OR b) running too large of a spark gap. The larger gap causes more voltage to be built up in the coil and the coil finds new and creative ways to arc. Note: theoretically it can be too small of a gap as well - weak spark, but more current flow.

Also note: the LS style motors had different coils at different times. Make sure you get the correct one for your vehicle.

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