C32 amg

[ammo1980]

Hi,

2002 C32 AMG, high mileage.

I'm getting a serious misfire after changing spark plugs. Any ideas?

Recent History:
There was a very slight misfire on idle. About once every 3 seconds. Never triggered engine light, but needed sorting. No code came up ever. This went on for at least a year.

Changed all 12 spark plugs, NGK Iridium swapped like for like (IFR6D10).

Cylinder 6 came back misfiring (code P0306).

Checked all spark plugs on that cylinder. Same misfire on cylinder 6.
Moved ignition coil to another cylinder. Same misfire on cylinder 6.
Replaced all plug leads on that bank, same misfire on cylinder 6.
Put a couple of old spark plugs back onto cylinder 6. Same misfire on Cylinder 6. The spark plugs removed were black carbonated despite being only few miles old.

Occasionally have had P0300 (Random Cylinder misfire) as well as P0306.

Any ideas on what to check for next before taking to a garage and checking compression? Can a new spark plug accentuate a problem with ignition?

Thanks for your help.

 

[BlackC55]

Try draining the fuel rail and checking the fuel pressure.

 

[ammo1980]

Hi

Thanks for reading and replying.

Engine ran fine today for about 4 miles. Wide open throttle, performance was back to normal AMG standard, and then a mile later the car misfired badly, Cylinders 1,4,5,6. Barely made it home.

I'm looking for the best way to drain the fuel rail. Can't find any AMG specific guides, is this the best procedure:

Pelican Mercedes-Benz Tech Article - Mercedes Fuel Injector Replacement - C230 / E320 / S320 / ML320 / CLK320 / SLK320

I've not messed with fuel rails or injectors before on any car. Should I just drain using the "Schrader valve", or go all the way to removing the fuel rail? Would removing the fuel rail automatically drain the fuel from the rail?

I will replace fuel filter as well.

Another question - why would the engine decide to misfire if the spark-plugs have been changed? How is this related to water in fuel rail?

Thanks,

 

[ammo1980]

Also, will this procedure return similar results as draining the fuel rail:

DIY "Pro" Fuel Injector Cleaning!!! - MBWorld.org Forums

Thanks again.

 

[BlackC55]

The miss can be caused by a faulty injector.

The fuel rail has no return and water can build up inside it.

The rail has a valve on the end of it. Use that to drain it.

Do a compression check too.

 

[ammo1980]

Hi, thanks. How many hours labour (approx) to drain the fuel rail?

Thanks

 

[markmifsud]

Hi, thanks. How many hours labour (approx) to drain the fuel rail?

Thanks

Why not try bleeding from the valve first, then if you feel you want to take the rail off for a manual clean you can do it in around an hour, maybe less.

 

[BlackC55]

Hi, thanks. How many hours labour (approx) to drain the fuel rail? Thanks

About 5 mins.