My 65 is misfiring on cylinders 7,8,9,11 and 12 on one bank and goes into limp mode/loss of power - this happened twice - both times when accelerating......CEL is staying on......it returned to normal operation after turning off and back on, but CEL stayed on.

Misfiring repeats itself and on hard acceleration, when car is running normal full power, I also get slight misfires when I let off the gas abruptly......

OPerating Temperatures are normal....

SO...... after I replaced all 24 spark plugs, that were fouled at 40K,..new ECU flash, and replaced a slightly cracked MAP sensor on the one bank where the cylinders in question are....it all happened again.....same symptoms....

FYI.....I also run Techron ever few months as a preventative measure - no luck there I guess, and I run the car pretty hard and highway trips to keep it running smooth...

I run 93 octane at BP, etc...better stations, although who knows....

Solutions?

Ignition coil pack/s replacement - ? Mechanic says okay (?)
Catalytic Converters - back pressure too much from bad cats? (Dealer 8 year Emissions Warranty covered?)
Crank Position sensor?
Ignition module for one bank?
ICP? don't think so....


Any other things I should be looking at?

Sounds like the coil pack you have on that side 7-12 is bad. Its hard to admit but sounds like its screwed. They are sensitive and even by changing plugs they get screwed.

Secondly ask our tech, there is a bulletin out there for MB spark plugs being gapped too wide. I think from mercedes they have them gapped at 1.1 should be gapped to.70cm I believe. This will also make the car misfire, but it seems its not the case since you dont have misifres on other cyl bank.

Appreciate your feedback......told my guy to replace the coil pack but he was reluctant since it didn't show a code, etc.....I think he will be open to that now and I have printed out your reply and also some other threads for him to assess......thanks again...

Scoured the forum yesterday....it seems ignition module problems are hard to diagnose......back to the shop Monday....

Catalytic converter defective causing back pressure.....and the misfires and limp mode......on to the dealer to replace the cats under warranty....

Cats were okay.....ignition module and secondary air temperature cooler motor.......$ 2,000 repair covered by Easy Care warranty....car back nect week...

Now the car has been diagnosed at the MB dealer with a bad ignition module
($ 900)and a faulty secondary air temperature cooler motor ($ 400 - related to intercooler pump)........

Cats seem to check out okay.......NOTE: only one cat to replace on a 65 according to diagrams as everything flows through the one cat......$ 4500 to replace plus labor.....yikes......

Expect car back next Monday.......we'll see if it returns to 100% operation....

So far.....my Easy Care warranty cost $ 4000 in July 2009......have had about $ 3,100 in repairs covered by warranty.....but it still is my money....warranty goes to 2013....

Repairs/maintenance not covered include trunk struts - below warranty deductible, front brake rotors, oil/brake fluid changes , new tires, and 24 spark plugs.....another $ 4,000 in total....

I must love this car......lots of money spent for a car with 40,000 miles, but it is a paid for car................all this repair/maintenance money spent in the last 13,000 miles or 2 years......about $ 7K......

May be time for a new car, selling it at 100% operational to the next guy....

Still have to change the V-Belt tensioner per manual and differential fluid at this 40K point......

The JOYS of German car ownership - having owned BMWs, Mercedes, Audi and Porsche..........I wish I liked Japanese cars more........my experience is that they are definitely more reliable than German cars and MUCH cheaper to maintain...change the fluids/tires/filters and GO.....

My 2003 C4S Porsche had $ 12,000 in warranty repairs over 5 years/70K miles and I sold it once the warranty was done.....I was a regular at the dealer.....don't want to relive that down time again.......

I guess I'll give this car another year max and then decide....

i have a 2005 cl65 with the same problem.. i replaced both coil rails and the coil driver which controls both coil rails and all sprak plugs have been changed, and fuel filter was changed also, next step is the cats. you mention 8 year emission warrentee for the cats.. does that rule apply for me? i am the second owner of the car?

Interesting. The wider gap might be a contributing factor as to why those coils fail- a wider gap requires the coil to work harder and hotter.

Well......got the car back from dealer with the ignition module replaced and secondary sir temperature cooler motor replaced for a cool $ 2,000 under warranty.....

Cat was fine.......

Took it out and gave it a good test of high and sudden acceleration and long idles, on and off starts, high speed, low speed stuff and the car seems to be fine now......runs real strong and starts better......

The dealer did say that if the CEL comes on again, it most likely will be the ignition coil pack on the one bank that was misfiring......we'll see......

So....I replaced the 24 plugs at the 5 year point per manual although early on mileage and paid about $ 600 for stuff not covered by warranty related to this issue....due to misdiagnosis by indie shop which had been perfect for two years in their diagnosis of issue with the car.......