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Can an active misfire (and the respective misfire error) go away just cause I deleted the error?


Topic starter

I mean - how is it even theoretically possible?

Here is the story:

Attempting to mitigate the LTFT discrepancy between left and right cylinders, I added a strong injection system cleaning liquid (Liqui Moly Effektiv Injection Cleaner) into my tank and drove like 180 km as one single ride. The engine behaved normally and ran smoothly, although the mentioned discrepancy did not seem to notice at all, that I was attempting to get rid of it.

The next morning, right after the cold start, I received the P0302 Cyl2 misfire error (smth I never ever had before on this car in my life), and actually noticed that the engine ran unevenly (yes it seemed to be real heavy misfire, not just a random error). I drove like 25 km with my scanner attached, and the misfire stayed with me the whole ride long, and so was the active misfire error.

Then I just turned the engine off, deleted the error, and started the engine anew. And it ran smoothly again, with no misfires whatsoever, whereupon I drove another 25 km with no problems at all.

Will try another cold start tomorrow, but now I am wondering:
- a misfire that severe must be obviously due to some physical condition not being OK - like misfunctioning injector, or similar fault condition. Such a physical condition cannot just magically disappear just because (and in the very moment) you delete the electronic error code caused by that condition, can it? Especially if this code reads "active", meaning that the fault condition is still being detected?
- what could have actually happened / caused this misfire, and how can it be eventually related to my attempt to clean the injectors, if at all?

I will also be grateful for any helphul advice on further troubleshooting. Thanks in advance!

About the car:
Mercedes-Benz ML 55 AMG 2001 w163 5,5l V8, no turbo, automatic, VIN: WDC1631741A297248, 243kkm.
Picture of a typical ML 55 AMG:!Alv3RQPn1ylAqE8bjbgqS9nj_mgh

P.S. The LTFT discrepancy between left and right seems cyls to be fuel delivery-related, since the LTFT on both banks lightly increases with load (like +3 to +5% under min. load vs. +6 to +9 % under medium to heavy load).

1 Answer

Probably a partially clogged injector that clears when it warms up.  Swap the injector (#2 you said) to another cylinder and see if the misfire moves with it.  Do the same with the coil pack.