Ash Pat

Dear MB World People,

I recently bought a 2001 MB S600 W220 engine vehicle. The vehicle is misfiring in the following cylinders according to the Mercedes Star diagnostic:

Passenger side 3 cylinders and Drivers side 5 cylinders are misfiring.

I have done the following to rectify:

1. Added fuel cleaning additive to the fuel, and then put in Shell Hi Octane fuel as the previous owner was using cheap fuel.
2. Then had the car fully serviced and oil changed to Mobile 1 oil.
3. Changed the MASS airflow sensor
4. Changed all 24 Spark Plugs to Iridium OEM NGK ones.
5. Changed the Voltage convertor.

All parts were Mercedes original.

Having done all of the above, the misfiring persists and the car does not drive, it just dumps the fuel.

To Note: When I changed the Spark plugs, many of them were oil covered.

Anybody have any idea what I can do next.
Your help and advice will be much appreciated
Many Thanks.

Arrie

It could be a problem with fuel injectors but as you have misfire in so many cylinders at the same time it is not very likely they all have failed at the same time.

One common thing for all injectors is the fuel pressure. If pressure is too low the spray from the injectors does not atomize correctly leading to improper burn of fuel in the cylinders.

I don’t know what the fuel rail pressure should be. Some other folks around the forum probably have the value for you.

If the pressure is low it is either fuel pump or pressure regulator problem.

Another thing is to check the crank shaft and cam shaft position sensors. These sensors play the major role in spark timing, which could be the reason for misfiring.

Ash Pat

Hey Arrie,

Thank you for your comments, I very much appreciate you taking the time to assist me.
Can I just check the following with with regards to the above:

1. If the crank shaft and cam shaft position sensors go, wouldn't it cause a loss of power and act like the timing was out.
2. There was enough pressure in the fuel line when I was taking off the coil packs to replace the spark plugs.

What do you reckon?

chassis

There are many threads on this site with V12 engine and ignition problems. The problems are few in number and thoroughly discussed. Try the search function.

Arrie

1. Yes. If crank shaft or cam shaft sensor goes bad it exactly can cause misfire or the engine won't run at all/

2. If the fuel pressure is ok then that is not the issue.

I have not done this in my own car but I understand the cam shaft and crank shaft sensors are not expensive parts so if you can DIY the I would go get them changed out.. They need to be replaced on an old car some day anyway...

vettebk

If I had to guess, based on what you have already done being done right, you have two misfires on the same bank. I would replace the coil pack on that side. The V12 uses one coil pack on each side which has 12 red silicon boots that can easily be torn or cut or burned through causing misfires. Sounds like two of your coils on the same coil pack on one side have fried. Check out Clark's site at v12icpack.com. I used his coil pack to solve my misfire problem.

Good luck.