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Same cylinder ignition coil

Looking for some insight before throwing more parts at the problem. 2007 Mitsubishi Endeavor. 190k miles. Misfire on Cylinder 4. Swapped coil with cylinder 2 and confirmed misfire moved to cylinder 2. Bought a used coil from junkyard (60k miles). Put it in cylinder 4. Car runs great.

Replaced all 6 spark plugs with new NGK iridium. Confirmed all plugs were correct gap out of the box.

After about 20 miles of driving, cylinder 4 starts misfiring again. Swap coil. Code moves. Looks like I killed another ignition coil.

Did I just get a bad coil or is there something going on that could be damaging the number 4 coil specifically? Computer problem?

Replacing a coil with one from a scrap yard is like replacing a light bulb that burned out after 1 year with a used 1 year old light bulb.

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Agreed. It’s not ideal but I’d expect it to last longer than a day right?

No, used parts have a life expectancy of 1 minute to who knows how long.

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Buying a used coil is like buying used underwear. Yuck.

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be happy that you got 20 miles out of a used coil and go buy a new one.

With the plugs out on a 190k miles engine I would strongly suggest a compression check. A cylinder that is dropping compression can lead to subtle plug misfires which can kill a coil…

Alright, well after the public shaming over buying a used coil, I broke down and bought a NEW coil. Installed it yesterday in Cylinder 4. It survived the commute home yesterday. Hopefully it’ll hold up. I will say that the new boot fits much tighter over the plug. I’m thinking electrically that used coil was probably fine but with age the boots probably shrink/dry and no longer insulate properly (best guess). Maybe it’s less about miles and more just time.

Thanks for the suggestion on compression testing. I should have done that when I had the intake off. I’m planning on changing the timing belt over the Christmas break. Maybe I’ll do compression test first though.