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?
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.