telpsicorei

Hey all,

I have a problem which i cannot figure out for some time now.

1999 w210 E55 AMG with 116k miles

Replaced spark plugs 30k miles ago.
Replaced MAF 30k miles ago.
Replaced Air-filters 30k miles ago.
JUST replaced the spark plug wires and tried to clean the MAF with MAF cleaner.
JUST did an oil change.
JUST did a tranny fluid change.

Here is my problem that started about 2 months ago and has gotten worse. It used to only happen pretty rarely, now its every time...

Engine idles okay. As the engine RPM goes past around 3500-4000 RPM under load, my engine throws misfire codes. but nothing else. Even when i put the trans in first, then slowly reach 3500-4000 rpm (practically no load) i have the same problem. My engine then runs really poorly (fewer cylinders) until i stop and restart the engine.

I unplugged the MAF, and experienced the same issues.

Things I'm looking at:
Coils,
O2 sensors,
a new MAF,
knock sensor,
camshaft sensor,
crankshaft sensor (prob not the last 3).

Any help before i have to throw more money into this thing???

Thanks in advance,
-nick

BordeauxW210

Are you getting a check engine light? You might also consider an injector as a potential problem, maybe a fuel system cleaner would help.

ohlord

and what type of plugs did you install?

Sathinas

You didn't mentioned fuel filter replacement...

You need three things to make a piston move down.

Air - you have that covered with new filters
Spark - Again, covered
and lastly..

Fuel - You have not indicated whether or not you've replaced the filter. At 116K miles, it's a good bet it could use a replacement.

telpsicorei

Yes, im getting check engine codes, but they only tell me of misfires. it doesn't seem specific to any cylinder, but then again when my engine misfires at high rpm usually i have to give it more gas when in traffic and it misfires more so. So i'll probably end up buying an OBDII reader and see if i can get it to point to a single cylinder around my neighborhood.

IIRC, i installed the factory plugs. single prong iridium. forgot the number FRDP332.. something like that.

Yes, i have changed the pump 30k ago as well as the filter. It may be fuel pressure, but i hooked up a pressure reg and was getting 55psi while parked, no clue under load.

telpsicorei

Also i dont think its the plugs b/c when i changed them they were perfectly fine. in fact my engine never ran better.

ohlord

cats


plugged cats will cause misfires.
get a scanner and post the codes
if the p0300 range codes are all on one bank of cylinders suspect the cat on that bank.

telpsicorei

Now that might be a problem. But is there a way to unplug them? Long road trip? Or at least confirm that they are plugged? Should I use some additives? Plus, the misfires were on all but one cylinder. Ill go buy a reader and try and reset the codes to maybe pinpoint the problem a little better.