Charles Joseph

2002 CLK55 with 33,000 miles. Check engine light is on. Error code reads Cyl. 6 misfire. The car is running very rough and you can smell excess fuel in the exhaust.

So far I have tried plugs, wires, #6 coil pack, and a new mass air flow meter. Car still misses.

It seems to do better when warm, but it still is not right.

Any ideas??????

Clk&Slk

It your O2 sensors.

Charles Joseph

O2 sensor would effect more then just cylinder #6.

mbenzman

Do you actually know which cylinder is #6 (second one back on driver's side)and what are you using as a scanner?

Charles Joseph

Do I know which cylinder is #6????????? Scans were done on a Mercedes Star diagnostic machine.

mbenzman

Have to be sure, not trying to insult!
I just noticed Kleemann (supercharged???) in your signature, might really want to go down to basics and test compression and cylinder leakage before going further.
Swap plugs,coil, and wires from another cylinder and see if you can move the problem. Listen to the injector for that cylinder and see if if firing. Check for a vacuum leak at that cylinder, like the injector seal. Blower pressure (if that's what you have) and small lean pops can wreak havoc and are more probable.
The more information, the more accurate the diagnosis.

Charles Joseph

Kleemann supercharged, ECU upgrade, and lots of other stuff. Swapped plugs, coil packs, injectors and anything else we could think of. Same results, misfire on #6. I have removed the computer and have sent it back to Kleemann. We will see if they find any thing wrong with it, either software or hardware.

I will check the compression as soon as I can. That is one thing we didn't check.

ProjectC55

Yep because a leaky ,burnt,or bent valve in the head in that cylinder could cause your symptoms including a blown head gasket. MBenzmann is 100% correct. I would be completely surprised if it's a SW issue!

Good luck and I hope it's a small problem like a bad injector or something.

mbenzman

Compression and leakage tests first, then scope the coil and injector so you know exactly what's wrong and go from there especially before sending ecu out and then having arguments because they can't find the problem. I would probably replace the coil and or injector on that cylinder if that's what it turns out to be.

Eurosport

as someone said above, i think it's an oxygen sensor
i've had similar problem a long time ago, took a lot of steps just like you did, until i got to change the oxygen sensor and all codes/misfires went away
but each car is a different case of course

mbenzman

But being a mechanic, you followed the steps first and the eventually left the "norm" in pursuit of the non-usual problem. I'd be embarressed if I sent the puter away and then found out I had a burnt valve or stuck lifter. I have also witnessed catalytic converters clogged on one bank that will not set misfire codes on every cylinder on that banks, but in that case we "usually" get at least two misfiring cylinders.
Sometimes you don't want go through the trouble or time to check the basics, but I feel it maybe important in this case.

Charles Joseph

The computer is already on its way to Kleemann in Colorado. If they cannot find anything then we will continue the search. It is not an O2 sensor, it is not a MAF, coil pack, plug, plug wire or any part of the wiring harness. All of these parts have been checked or replaced. Compression check cannot be done until the computer comes back.

Eurosport

in my case, i was not getting any oxygen sensor codes, but the sensor was beginning to fail, not failed completely to give a oxygen sensor code, and i had same symptoms as you mentioned. after going through a lot of trouble trying to pinpoint the problem as well as unecessary replacing some parts like coil packs, plugs, etc., once that oxygen sensor was replaced it fixed the problem for me.

i hope you get some answers soon though sounds like you went through a lot already.

mbenzman

You could perform a cylinder leakage test (which is what I prefer anyway as compression tests can lie) without having to crank the engine. If you want to do something while your waiting.

BeNzTeK

had his happen to me try fuel injector on that cylinder if not that drop the exhaust and run her may be a cat

Charles Joseph

Number 6 cylinder has only 80 PSI compression. The others cylinders are at 180 PSI. Now it has to be scoped to try and find out why? Hopefully it is just the valves and not the rings, piston or worst of all the block! OUCH! Thanks for the input everybody.

Zoom On

So what would be the cause of a smoked valve? That can't be good.

mbenzman

Sorry to hear that! Since you insist on compression and not leakage, get an oil can (the hand held trigger type deal you never see anymore and put some oil in it) and then squirt about ten shots into the cylinder. Use a long piece of vacuum hose to get into tight places but remember to prime hose. Then crank engine over and see if it temporarily comes back up. If it does=bottom end, does not=top end.
If you place the engine at tdc on the power stroke for that cylinder, and get an adapter to screw into the cylinder to put compressed air on it, that will also tell where your leak is, crankcase = rings/piston, exhaust = valve, cooling system = head gasket, intake = valve. neigboring cylinder = head gasket, etc..
If the valves are leaking, take the rockers arms off and see if the lifter is stuck holding the valve open, or trash on that valves seat, such as carbon.

Charles Joseph

The car is having a leak down test Monday morning. I will know then if it is a valve, gasket or a piston problem. I am hoping it is a stuck valve. Will post more when I know what is going on.

SeaCoupe

Wow, I'm hoping the best for you on this. This could get expensive for you.

E

Charles Joseph

Number 6 rings are gone, and yes its gonna get expensive!

Zoom On

ouch, what would cause that with only 33k on it?

SeaCoupe

How in the heck does that happen with 33k miles on the car. This just doesn't happen. While I'm unfamiliar with this specific engine, I can't recall hearing about this problem at 33k miles. Not unless the car was beat to hell.

Well, the good news, is that if you go into it, you'll have some serious peace of mind knowing the engine should go over 150k. With the heads off you could also thing about getting a port and polish job.

E

mbenzman

Did you scope the cylinder? I have a hard time believing the rings are gone unless the engine had detonation and broke the ring lands on the piston.
I had a 300E with 30K. miles that had the ring gaps lined up on 3 cylinders and had 90% leakage on those cylinders. Disassembly of the short block, rearrangement of the rings and reassembly cured the missing.
I would be scoping that cylinder to look for any visible piston damage. Scoring on the walls, melting of the edges on the piston crown etc. Maybe if your lucky the rings are migrating and it could possibly go back to normal.
More info is helpful for a better diagnosis. Has this engine ever seen any nitrous? Burnt pistons aren't normal as they are oil cooled in this engine.

Charles Joseph

They scoped the cylinder and found nothing. No scratches, no holes in the piston, it all looked good. Thats why they think the rings are the problem. Never thought about them lining up. I will run it by the mechanic.

No nitrous. Never will, don't believe in it. Bottle empty=no more power. 1 burp=blown motor. Not a combination I like.