Missfire on W203 C240.

[Jerry May]

HELP NEEDED. I have a late 2000 C240, chassis W203, 41,000 miles.
My problems started with bad running last summer so the MAS was replaced, everything ok for a few months. 2 weeks ago in the upper rev. range car develops missfire, engine light flashes, car then goes into limp mode, stop the car and restart the engine everything back to normal except now engine light stays on. Took it to MB dealer to have the fault code read and it comes up with missfire on 4,5, and 6 cylinders (left hand bank), they are not sure what it could be, they say it might be the front, left hand Lambda probe. Anybody know of the problem? The cat has been taken off, inspected and found to be ok.
Jerry.

 

[Blobcat]

Hi & Welcome,

There is some info in the attached thread; http://forums.mercedesclub.org.uk/showthread.php?t=17650 whilst that was cured by a new MAS there is other info which maybe of use.

 

[Jerry May]

Missfire C240, (W203)

UPDATE, front left lambda sensor has been replaced with a new one but the missfire is still there (top of rev. range),
PLEASE HELP!!!!!!!
Jerry.

 

[jonathanjhann]

Think you will find that it will be the coil leads. They are prone to breaking down internally.
I would just replace the whole set.

 

[Blobcat]

Did you have a look at the link posted above?

 

[mercdriver]

hi, this happened to me when I first bought my C240. Everytime I pushed it (to the higher revs) it started to mis-fire and went into limp mode. Friend connected diagnostics to it and reported misfire on no.5. Took it back to where I bought it, they replaced no.5 plug lead but to no avail. They in turn took it to Mercedes stealership, who basically scratched their heads. Now what happened next, I can't offer an explanation for, but I was told that they took the car out, put the gearbox into manual, and accelerated to the red line on each gear (I think this resets the gearbox). This did not cause mis-fire. They done this a few times and the car has been sweet ever since (says he tapping loudly on the wooden desk). I was not there, I did not see it, but this is what they told me. All I know is the problem hasn't returned.

Cheers

Mark

 

[Jerry May]

Missfire,

Thanks everybody.... Mark my C240 is a manual but the problems sound the same. The plan today is to get the ECU out of the car and tomorrow send it to be fully tested.
Jerry.

 

[Jerry May]

Help....this might be my last Merc.!

This saga just get's better and better!!!... disconected the battery like it said in the manual to pull out the ECU so I could get the serial numbers off it, and guess what??? now have a dash malfunction, can't get in the boot, no wipers, no fuel reading, and more,
Jerry.

 

[robbo]

You've just blown the rear SAM module. It is common for it to blow fault when disconnecting/reconnecting the battery. I believe there is a procedure you need to follow when reconnecting the battery to prevent this happening.

Should cost about £300-400 to fix at a stealer, I would guess.

 

[ALAN@ECUCLINIC]

May I Stick My Nose In Here?
If You Need Your Ecu Tested May I Put Forward A Realy Nice Guy......me!!

 

[Jerry May]

Everything working fine now.

Disconected the battery and reconected by putting the earth on first then carefully putting the positive on.... everything now is working fine.... Our top Sparky at work says this is the safest way not to damage any of the cars components as you have a realy big earth that can get ground a power surge much faster than the components themselves.... I know there is going to be letters now saying the oposite but it's funny that every part of my car that had shut down are now working fine, without a trip to the Stealer,
Jerry.

 

[robbo]

Result!

How's the misfire now?

 

[Jerry May]

.... Can't get it to missfire now!!!!
Jerry.