Multiple random misfires but only on cylinders 1 and 6

[DSM10000]

About a month ago the C320 started throwing up occasional fault codes for multiple random misfires on cylinders 1 and 6 (only these two) always a few minutes after a cold start

Apart from the EML there was no other indication, the engine ran and performed as usual , as a service was due I also had all 12 spark plugs changed (Bosch) as well as both air filters, oil etc and fuel filter.

Despite this it has thrown up the error again last night about 3-4 minutes after starting, there seems to be no connection with outside air temperature etc

Once warmed up the fault never appears so I am a little lost as to where to look. If it were coil packs I would expect it to be a constant misfire.

One suggestion I have had (non MB mechanic) is a faulty MAF but I can not work out how that would only affect cylinders 1 and 6?

It will go to my local MB specialist when he is back from holiday for a Star session but any pointers gratefully received.

Thanks as ever.

 

[DSM10000]

Just to update:

No incidents on the last three cold stars, I did check the plug leads, all were firmly in place and no evidence of any moisture ingress anywhere near the coil packs etc.

Can Star test individual coil packs and injectors?

 

[Auto-mobile]

I assume it's a w203 m112 v6 petrol? Have you checked for water in the fuel? There is no fuel return so what gets pumped up to the engine gets used, if you have picked up water from a poorly maintained filling station it can cause random misfires.

 

[DSM10000]

I assume it's a w203 m112 v6 petrol? Have you checked for water in the fuel? There is no fuel return so what gets pumped up to the engine gets used, if you have picked up water from a poorly maintained filling station it can cause random misfires.

Yes that is the engine.

I now remember my Indie telling me this some years ago when I was getting a misfire on number 6 if I used the engine "enthusiastically".

Not sure how to check for water in the fuel, if that were the case would I not get random misfires more regularly and not just on a warm up from a cold start?

Thank you for your reply.

 

[Auto-mobile]

If my memory serves me right the fuel rail is a u shape 1 and 6 are at each end of the "U" so to speak, enersha pushes the fuel backwards when you move off, if there is water present it moves towards these cylinders.

Remove the fuel filter and drain into a clear jar to check for water.

 

[DSM10000]

Fuel filter checked, no sign of any water in the fuel that drained out so it looks like a Star session is required

 

[Doe1000]

Used up fuel and fill up again. possible bad fuel batch.

A workaround for misfire is to warmup the engine before you set off. i saw this often in developing countries.

 

[markmifsud]

If my memory serves me right the fuel rail is a u shape 1 and 6 are at each end of the "U" so to speak, enersha pushes the fuel backwards when you move off, if there is water present it moves towards these cylinders.

Remove the fuel filter and drain into a clear jar to check for water.

Also on the left hand side of the fuel rail there is a bleed valve, release this to evacuate any remaining water in the rail.

 

[DSM10000]

Solved

Having changed the fuel filter and drained off fuel from the rail the problem seems to have gone away.

Many thanks.

 

[edc]

I guess you could try swapping the coilpack with a known good one and one where there is no mis-fire it the problem returns.