johnng117

Hi guys, I hope someone can shed some light on what I should do...

3 weeks ago on start up the engine light came on and the error code was P0304 Cylinder 4 Misfire Detected, it was running lumpy. Considering that my last spark plug and plug change was about 100k ago I thought I should just change all the Ignition Coils (Bosch), Spark Plugs (NGK LASER IRIDIUM), Ignition cables (MAGNECOR KV85 8.5MM) and I decided to change all the injectors (Bosch) too. 2 days ago after changing all the ignition parts the car started up great and the engine response was back, it was smooth for about half a day. The following day on a start up again I had the same error again. Does anyone have any idea why this could be happening, after switching off and starting again it starts without problems. But you do feel a slight vibration through the steering wheel on idle which does seem like something not running smooth.
The car when driving is fine and smooth, power delivery is good too but I'm sure something is not right with the electronics as this morning it gave me a Cylinder 4 Misfire again, but after a restart it seem ok.

I would appreciate any input, if someone also had a similar problem I would love to hear from you..

chassis

Mods on this vehicle?

Replace sensors (cam, crank, O2, water temp, air temp) if this hasn’t been done. On old cars like this most electrical components need replaced.

Celeris AMG

They say that MAGNECOR cables fail, the connections loosen.
Original cables are better.

johnng117

Just now I have changed all the plugs back to stock, still the same. First start sometime its lumpy (same error).

johnng117

These sensors will effect Cylinder 4 misfire?

cdk4219

This can also be a spun cam lobe, that’s how it starts. Not saying it is, but it seems to be a problem that is hard to diagnose. # 4 was one of the the cylinders that destructed itself in the 112k I bought. The previous owner spent lots of money trying to figure it out. Ran well off idle, but spun I believe the exhaust lobe I would go for a compression check on that cylinder and rule that out.



there’s the aftermath, and upon checking the cam, the lobes are off. Hopefully yours is an injector or something much simpler

chassis

It's a system. If any of the components are borderline, which in an old car is certainly the case, unexpected things happen. I am a throw-parts-at-it guy and these are the parts I would throw at it, to rule them out of the picture.

johnng117

Today I check the fuel pressure at the rails and its healthy, compression test passed too.

One thing I didn't mention, when cylinder 4 is misfire, I get a whining noise come through my speaker. After a restart and everything is fine again, with the whining gone.?? So strange?
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brauhaus313

Did you check your wiring at the connectors and along the line for breaks/corrosion/rat damage?

Throwing parts at it, especially things that have nothing to do with a single cylinder misfire is not a good approach.

chassis

Mods on this vehicle?