My daily driver is a 2013 Mercedes E550. A few days ago it suddenly started running rough/missing at about 45mph. The check engine light came on. It was rough at idle when I stopped. When I got home I shut it off. A few minutes later I restarted. At restart it was running smooth and the check engine light was off. I hooked up my OBD computer, no codes. Any ideas from the experts here? FYI About a month ago the check engine light came on but the car was running fine. I checked codes and got p2096(Post Catalyst Fuel Trim System Too Lean) I reset the codes. It does not show up now.

Hi Too , What Engine and How many Miles on this Benz ?

wouldn't post cat fuel trim indicate something going on in the post cat o2 system ?

You run high test? Where have you gotten fuel from? Same place both times?

Answers to earlier questions:

What Engine and How many Miles on this Benz ?
E550 is a twin turbo V8
It has 110,000 miles.

wouldn't post cat fuel trim indicate something going on in the post cat o2 system
Yes, but I don't know if the P2096 code from a month or so back is related to this problem. I cleared that code and it hasn't come back.

You run high test? Where have you gotten fuel from?
I always use 93 octane premium fuel from the local Shell station.

Thanks all for the responses.

That's an M278 engine.

Locate the cam magnets on the front of the heads. Two black covers with e-torx screws holding each one on. Pull the plugs off the sensors and look for oil in the connectors on the wire side.
If you find oil you need to pull the connector off the engine computer (ribbed aluminum unit on top of the engine) and look for oil there.
If oil is found at the computer you're in for a big bill. That means you will need to check for oil at the ignition coils and other sensors on the engine.

The early M278 engines had that issue. It was fixed by 2013.

Here's a good place to search or ask a question: https://www.benzworld.org/forums/

Go to W212 E550 forum (I think that's you model?)

Mike

Have you ever replaced the fuel filter?

Does this use an EGR valve? I've experienced those symptoms on multiple brands when the valve sticks open. GM were awful about carbon buildup.

Yes, the fuel filter was replaced about 20,000 miles ago.

What seems unusual to me is the check engine light came on then reset itself leaving no codes. Is that normal?

Benz World thinks you need an O2 sensor replaced?

Depends on what the code was. Some will reset if they pass later testing.

Did you do as Feets suggested????? He just gave you a very logical place to look and he has a wealth of knowledge on these cars.

Feets suggestions are over my head. If it happens again I'll have to take it to MB.

Feets suggestions are over my head. If it happens again I'll have to take it to MB. [/quote]


Sounds pretty simple to me. Just the mater of locating the connectors, unplugging them and inspecting for oil wicking.