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A 2018 Duramax with a phantom misfire cost me two full days
Had a truck come into the shop last week with a rough idle and a check engine light. The code pointed to a misfire on cylinder 3, so I figured it was a simple injector swap. I put in a new Bosch injector, cleared the code, and it ran smooth for about ten minutes before the light came back on. Spent the next day checking the wiring harness, the glow plug, and even swapped the injector to a different cylinder to see if the problem moved. It didn't. I finally broke down and did a full compression test, which showed a small but steady drop in that cylinder. Turned out to be a tiny crack in the piston crown you could barely see. That simple injector job turned into a full teardown. Has anyone else had a misfire code lie to them that badly on a newer diesel?
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james_martin931mo ago
That's a brutal way to find a cracked piston. @christopher_west1 has a point about the code just showing the symptom, but man, it still feels like a trap when everything else tests fine. How do you even begin to suspect a piston on a truck that new without chasing every other possibility first?
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Totally disagree that the code lied. It told you exactly where the misfire was happening. The computer can't see inside the piston, it just knows cylinder 3 isn't firing right. You followed the normal steps but the root cause was just way deeper than usual. I've seen plenty of weird stuff cause a misfire code, like a bad fuel filter messing with pressure on just one cylinder. Isn't it better the code pointed you to the right area instead of giving you nothing?
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