Misfire that is driving me crazy

[w221 s350 2006]

Greetings all dear members,

I have a w221 s350 2006, first it was misfiring, I changed the plugs switched the coils and it didn't work, then I went to another shop, who suggested that I change the battery. I did and it didn't work. Then someone told me that it's pressure is not good. I suspected that was not a correct answe as the misfire would go somtimes when I switch off then on, I checked with another shop they said pressure is fine but it's an ecu problem, I chnged the ecu and it misfired then on the new ecu I changed one misfiring coil and magically it worked like a bee, then later I said to my self I should change all coils and plugs, so I bought kella and boschwhen I installed the new stuff it misfired again. Then later on the misfire was on two cylinders, I went to the shop, changed the ecu the misfire disappeared for a short time, to reappear shortly, he said it's the MAF, he disconnected it and I tried it it was shaking but not misfiring, he plug it again and it didn't misfire until next day, it sarted to misfire again.. I think I said misfire like a 100 times, but it's really driving me crazy, if you can help me I would relly appreciate it..

 

[DSK]

I take it your plugs are all the same brand and your coils are also the the same brand as each other? Also only premium or OEM options should be used and not the cheaper offerings.

Even if the EML is not on, has it been read for any codes?
When was the fuel filter last changed?
Anyone tested the flow rates of your injectors?
Anyone tested the fuel pressure, fuel pump?


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[brandwooddixon]

From what you say the misfire is inconsistent and you've already replaced a lot of parts.
Has the engine earth strap been replaced? The car is nigh on 18 years old, would be worth a try and very cheap.

 

[w221 s350 2006]

The plugs are the same, mercedes original, the coils are different, they're delphi and hella,
The there are faults, like p301 always showing
The fuel filter I didn't change
No one tested the injectors
No one tested the fuel pump or fuel pressure
When I turn on the car in the morning, it starts normaly then starts to make something I call hiccups like the cylinder is misfiring then coming back to normal, then the misfire continues
I changed the coil for this misfiring cylinder myself, when I remove it from the spark the electric spark coming out of it was not consistent, this was something I noticed maybe I misfigured how to check this but this what happened

 

[w221 s350 2006]

From what you say the misfire is inconsistent and you've already replaced a lot of parts.
Has the engine earth strap been replaced? The car is nigh on 18 years old, would be worth a try and very cheap.

Thank you for your suggestion, I will give it a try

 

[DSK]

As your coils are a mixed bag, I’d ensure they are all the same. Whilst technically a coil should work, a mixed set can experience differences in tolerances.


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[w221 s350 2006]

I have a cheap obd2 and I wanted to share the results, if you can help me

 

[brandwooddixon]

I suspect that the emissions related ones are all related to the misfire. There seems to be a lot of other faults that would be unrelated to the misfire directly, but it suggests to me that there may be a common electrical issue. Hence get checking continuity and resistance earth straps, including back to the battery.
It only takes a missing or poor earth to trigger multiple faults as voltage levels will bounce around.

 

[w221 s350 2006]

I cleared all the faults, the p301 fault keep coming, I tried to replace the coil nothing happened

 

[Malcolm Johnson]

P301 Cylindar 1, spark plug good? coil good? fuel injector good? fuel and electrics all good to cylinder 1.