So, I was accelerating to pass a truck on the interstate today and all of a sudden my car started shuddering like it had a misfire. I took it to the local auto parts store and they read the code and said it had a misfire on cyl 1, 3, and 4. I have previously (about 10,000 miles ago) replaced those (1,3,4) ignition coils with Beru brand coils and 4 new Bosch plugs. I was inclined to think that it wasn't the ignition coils, but Advance had them in stock so I replaced the 3 in the parking lot and cleared the codes. When I fired the car up, thinking all would be well, it still had the same shudder, but now was throwing 2 of the same code for a misfire on cyl 4.
So what could this be? My brain tells me its not the ignition coils, since they were pretty new and swapping them at the store didn't help. I also don't think its the plugs after only 10,000 miles. I got the second codes for cyl 4 immediately, so I haven't driven it around to see if any other codes pop up, but it is confusing that the code for 1 and 3 went away.
Sudden failure of more than one coil or spark plug is very uncommon but anything is possible and your case it looks like they were not the root cause of the misfire detection. Initially it sounded like there might be a fuel delivery problem based on the high load condition when the fault occurred, however, the fact that it is still misfiring on #4 suggests that something else is "amiss".
The electrical connector plugs for the coils are known to get brittle over time and cracks the lock tab off, this can allow the connector to fit loose on the coil and cause misfires, make sure this is not your problem first.
The easiest thing to do next is to swap a coil and spark plug from a cylinder that is not registering misfires, such as #2, onto #4 then clear the codes and see if the misfire code follows the coil/plug set. If it does not follow them then the problem is truly on #4 and possibly due to air/fuel mixture issue such as a vacuum leak, poor injector spray, or compression loss. There are other anomalies that can cause misfire but these basic steps have to completed first.
If there are any other fault codes found in the engine control module, make sure you post them up as well.
The bottom plug is from cylinder 4. Safe to say at the minimum I have a plug issue. And I must not have put plugs in like I thought, These are Denso brand and I never would have put those in.
Hopefully the plugs are the only issue and it looks like they have at least 80k on them. The deposits on the #4 plug suggest oil contamination but if you drive them with it misfiring for a while you will get deposits because there is not enough combustion heat to burn them off. That plug also looks like the ground strap is burned back like there was some pretty serious detonation, this can happen if the engine is leaned out under high load, run under high load hot or, if tuned and the timing is too high for the fuel grade. If it was mine I would have to do a compression test just to sleep at night but You should know if its hurt within the first 100 miles.
My 2014 ml350 check engine came on and truck started running like crap. Took it to MB dealership they changed the distributor and said reposted some ignition coils. Probelm went away came back a month later and they said have some coil misfiring and replace coil #6. 4 months later problem came back, took it to different mechanic and they recommended changing all the coils. I did and problem went away for two months and back again… what else can it be??
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