alexstaar

I have a 2003 W203 C230 Kompressor (built in 12/2002) with the M271 engine with 129,000 miles. I just recently had the thermostat replaced because it was stuck open for about 6 months. Shortly before I had the thermostat replaced, I was doing some spirited driving on the interstate (WOT on the interstate near 100mph) and the engine started to misfire. Prior to this, my gas mileage had been slowly, then quickly declining. I used to be able to easily get 27-29 mpg cruising at 80 mph and 23 mpg city, and now I can't get any better than 20 mpg highway and around 14 mpg city.

I started reading a bunch of forums and such and became aware of the 2 service campaigns available for my car so I took it to the dealer and had them completed (this was the $12 vent/vacuum hose and the solenoid sensors). Then I took it to my mechanic and made him aware of the problems and symptoms. He replaced the thermostat and started troubleshooting the system too lean issue.

He replaced the oxygen sensor along with the spark plugs because they were completely burnt off because of the lean condition. This didn't fix the problem. I then had to go back to school out of state, so I had to take it to the dealer out of state to continue troubleshooting. I took it to the dealer and they said it may be the MAF, but they said if it didn't fix the problem, they wouldn't charge me and would put the old one back on. It didn't fix the problem, so I got the car back. I disconnected the MAF to test if the dealer's finding was true and it was. The engine still misfired with the system too lean. The thing is that it only misfires under load (4,000+ RPM in 2nd, 3rd, and 4th gear) and not when it idles or normal driving (less than 3,000 RPM). Also, the misfire occurs randomly in any of the 4 cylinders, it's never the same cylinder. The system too lean code is always P0171 and it sometimes throws the P0170 code as well. So now here I wait. I just talked to my SA today and he said the only thing they can do now is keep it for a few days and charge me a few hundred dollars diagnosing the problem.

I'm not sure what else to do but to continue with the dealer's diagnostics. I've heard it could be the fuel filter, valve issue/compression issue, a vacuum leak, or the fuel injectors. What do you think it is?? Any help or advice would be appreciated!

mercedes4ever

I would avoid dealers & look for a Indie MB Specialist, far cheaper & better imo.

Two things that come to mind on reading your issues;
1. What Octane fuel are you using? too low an octane can cause pinging etc. Should not be using < than 95 octane.
2. Timing chain could be jumping a tooth IE stretched / worn. This can be diagnosed by starting the car cold in the morning, hood up, listen to see if you can hear a "rattle" coming from the engine initially.

"I then had to go back to school" Q: Why would you buy a Mercedes $$$, especially one with high miles if you are a student?

alexstaar

I always use 93 octane and have never put anything lower in it. I've had it since the ODO read 90,000 miles.

I have heard of the timing chain issue common on this engine, but I have never heard the notorious rattle coming from my engine. It does run and sound a little rough if it's cold outside or after I just cold started it (it almost sounds like it's knocking or pinging), but once it warms up, it's completely smooth.

mercedes4ever

MB State NOT LESS THAN 95 Octane! That knock or pinging when its cold, is the timing chain I would suggest. Replace before it lets go or you could be in for an engine rebuild, which is more than the cars worth.

mercedes4ever

or M111

alexstaar

I'm pretty sure my book says not less than 91 octane, but I'll have to check! 95 octane isn't available around here... 93 is usually the highest you can buy. I'll listen for the timing chain when I start it tomorrow morning.

But this doesn't help the system too lean issue

alexstaar

This looks like an M111 engine in a W202. But the timing chain could definitely be an issue for my M271.

mercedes4ever

Sorry, think your correct...same principles apply though.

mercedes4ever

If its slipping... it will throw the timing out!

alexstaar

That's true. Can I easily access the timing chain with basic household tools or no? I could check to see if it's stretched, right? If yes, could you direct me to a forum with the proper instructions on how to do so? Thanks!

alexstaar

I will post a video of the cold start tomorrow and maybe someone could tell me if sounds like the chain is bad.

mercedes4ever

Good Idea, then worry about changing it or not after that.

alexstaar

Here is the cold start video of my car. Does it sound like a failing timing chain?

mercedes4ever

Hard to say, there is some excessive noise there but it is not extreme. Take it to a good Indie MB Specialist.