1998 Mercedes s320. Misfires under load. But, when I restart, she runs like a champ till i give her a load.

 

Fixed it! gave her a tune up. but now when its cold, if i floor it, it will miss. only when cold.

 

Hi

I have a 2000 W208 CLK320 with a similar problem.
She too runs like a dream until hitting around 4300rpm. A miss develops and holds until restarting.

So far, I have replaced:
- Plugs
- Fuel Filter
- Air Filter
- HT leads to coilpack 4
- MAF Sensor

What did your 'tune up' include and have you gotten rid of the miss when cold?

Thank you in advance
Shane

 

My 2000 W220 S320 with the same engine as your CLK, gave me the same problem.
After switching HT Leads and coils from cylinder to cylinder to see if the problem followed (with no result),
I replaced the MAF, but the problem did not clear immediately (although a slight performance improvement occurred). I was just ready to replace the CAT, since the MB Dealer said 3 cylinders in the same bank misfiring could be the effect of bad CAT...
BUT...
I just wandered if the ECU was just needing time to self-adjust after so many hours of running with bad feedback from the MAF, so I have tried to run on Manual Gear shift instead of automatic always trying to keep a high RPM, let's say 3000 RPM average, and also pushed heavy from 2000 up to 4000 RPM, just under the threshold for the misfire problem to appear, to allow the ECU to self-adjust at higher RPM.
Slowly the problem moved up to 4500 then to 5000 RPM.
After one week the problem had compleately cleared.
My mechanic with the testing equipment has shown me the ECU had corrected air:fuel ratio more than 30% thanks to the long-term feedback data from the new MAF.
In case you solved in a different way, can you please share your experience?

Best regards.
Max from Italy.