Cls55 AMG misfire at 3,000 revs +

[gunning]

Afternoon gents, I’m hoping an expert can guide me in the right direction.

I have a cls55 and it’s playing up, it’s at the Mercedes specialist and he’s struggling with it.

Drives fine up to 3000 revs and then starts to surge, let off and it’s ok again. If you fully plant it and try to get it to rev out, it really isn’t happy and shuts down cylinders.

It has had all new spark plugs which didn’t do anything, fuel is reading 5 bar, it has a fault in there for post lambda but he doesn’t think that’s what will cause it and doesn’t want to replace parts for no reason.

It runs sports cats and but other than that it’s fairly stock as it did have a tune on that was taken off as it was blocking some of the fault codes coming through.

He’s at his whits end and I’m left with a broken car. Can anyone help? Has anyone had this before?

 

[AMGeed]

Has your specialist checked the coil packs?
After the plugs, thats where I'd start.
Has this specialist got Star diagnostics?
I don't see how a remap would block any fault codes from appearing.

 

[gunning]

Yes he’s been an MB specialist for 20+ years and mb tech before that. Yes he runs star diag.

All the obvious have been checked.

Remaps can map out fault codes now so a return to stock was important, probably the most common map is for fault codes now, not power.

 

[fabes]

Fuelling, despite the 5 bar reading?

There are other Mercedes Indi on here who might chip in.....

 

[merc85]

Failing fuel pumps under load? If memory serves me correct they run two pumps perhaps one is getting weak i had similar with my s211 e55k
Post lambda probably reading a lean or rich emission as it misfires.

 

[alabbasi]

Ignition would be the first thought, how old are the plugs?
I also remember having oddball behavior in my S55k at higher RPM when my intercooler pump started going that out.

 

[gunning]

plugs have all been replaced in this process.

I’m not sure it’s intercooler pump as it happens from stone cold not repeated full throttles.

Could be fuel pumps but he did test the fuel pressure out on drive apparently which is when it gave the readings of 5bar