clk 55 amg misfire

[Frankho9]

Hi

My CLK 55amg has a misfire which is driving myself and mechanic nuts, its 2003 model, no fault codes, been on star machine,

Changed Plugs, Leads, MAF, core packs, injectors tested, new injector seals, rail pressure good, compression tested, new hoses,

after checking internet i can only find two other options, intake manifold gasket or ECU,

Any suggestions greatly appreciated especially if you have experienced anything similar,

 

[SL03WLY]

Hi,

Could you confirm which brand of plugs you fitted please? and the brand for the other parts? I remember using some cheaper Beru spark plugs which didnt work well, changing to NGK worked well.

Thanks

 

[Frankho9]

Hi
Thanks for the reply,
Tried ngk iridium and Bosch
MAF was from Ebay says original , race leads Ebay £200.00 highly rated everywhere i checked, injector seals from Germany as nobody including Mercedes had sets with all parts,
but the misfire began before changing the parts and these were all attempted remedies

Thanks

 

[SL03WLY]

The MAF, was it a genuine part or similar like Bosch and was it new?

 

[Frankho9]

New part, Delphi

 

[fabes]

Fuel quality issue?

 

[Frankho9]

? dont really understand, only ever had higher grade fuel and filters and pump checked as good

 

[AndrewOl]

Have you carried out a compression test?

 

[Bellow]

When does it misfire? Under what operating conditions?

 

[TDE1again]

They often have lumpy idles.
My 55k does.
As Bellow said, when does it happen?

 

[Frankho9]

it has been compression tested, happens at low revs once warm, just a stutter as accelerating,
disappears at higher speeds,
mechanic says burning lean one bank,
i did find a thread last night on here looked promising, c63 similar/same issue, was Cat so have mentioned that to the mechanic

 

[m2287]

If you plug it in does it say which cylinder is missing?

 

[Frankho9]

nothing showing misfire when plugged in,

 

[Bellow]

, happens at low revs once warm, just a stutter as accelerating,

If you mean on initial opening of throttle - misfires on tipping into the throttle are usually (but not always!) caused by ignition failure on the high voltage side. (The spark falters when being asked to appear in the cylinder when there is higher pressure there after throttle opening. NB, moderate throttle openings (not WOT) are enough to cause this at low rpm).

mechanic says burning lean one bank,

If they have evidence of this then obviously a possible cause.

 

[Frankho9]

Thanks, that definately
sounds like a good test addition,
when i mentioned cat to the mechanic he said he has seen that occur 3-4 times in 35 years but thinks the symptoms could add up to that, he is planning to check over the weekend, in the meantime i will add your advice to the list of possibilities and mention to him,
many thanks, keep you posted