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. I have always used 93 octane in it and ran techron in it several tanks ago. I posted a link to a cold start of the engine because it could be the timing chain?? I sure hope not though. What do you think it is?? Any help or advice would be appreciated!

I started a thread in the "New Members Check In!" forum last night, but couldn't figure out how to move it to the W203 forum. Here's the link to it: https://mbworld.org/forums/new-membe...nder-load.html

Glyn M Ruck

Check all vacuum & breather pipes for a leak.
Check Fuel pressure on the front injector rail at the Schrader valve. s/b> 55 psi ot 3.8bar.
Are you getting any misfire codes 300, 301 etc?

alexstaar

Yes if I give it WOT, once it gets over 4k rpms, it starts to misfire, usually in just a single cylinder. It then throws a P0301-P0304 code.

I don't have the tools to check for vacuum leaks/smoke test or fuel system pressure. Unless there is an easy way to check, I'll have to take it to an Indy shop at the least.

C3Duece

old schoolers would spray carb cleaner around suspect leak areas while the car was running. If idle changes at all after spraying you've found your leak. Just don't go spraying any red hot manifolds. Do it on a cold/cool engine.

alexstaar

My dad ended up wanting to take in to the dealer regardless of how much they screw us over. Dealer spent almost 8 hours diagnosing the problem and ran all kinds of tests and determined it's the whole wire harness that is malfunctioning. I already had the recall/service campaign work done to it regarding the cam shaft sensor leaking oil. They replaced the wires/plugs to it, but not the sensor itself. Shouldn't the sensor be replaced since it is still leaking oil? If it wasn't included in the campaign originally, should I have them replaced? I took off the plug to see if there was oil present in the new plugs and there was, but not nearly as much as before with the old ones. Could oil be getting into the wire harness from somewhere else where an o-ring of some sort needs to be replaced?

Glyn M Ruck

If the engine harness is saturated with oil it will have come from leaking cam magnets.

alexstaar

Issue Solved:

The dealer replaced both oxygen sensors, the MAF, and replaced the wire harness. They said the cam magnets were replaced when the recall was completed. The car runs better than it has in 2 years! And I have all my gas mileage restored! Got an average 32.8 mpg cruising at 74 mph. Very satisfied.

Glyn M Ruck

Great ~ pleased it's sorted. Watch those cam magnets for oil leaks. Did the dealer fit pigtales?

alexstaar

Not sure what you mean by the pigtales, but this is the final result of the recall that was done. They did change the wires running to the cam sensors and the sensors themselves and installed what looks like some type of adapter.

Glyn M Ruck

Yes they have fitted pigtales. Good. If the sensors leak again they will leak into the pigtales & not the main harness.

alexstaar

That's good news! Now hopefully I will never have to spend $1200 to have an oil drenched wire harness replaced again!