mercjames

I have a 2013 C250 with 56k miles and recently have noticed some issues at cold start. When I start the engine it runs rough like it's misfiring and then levels out after about 30 seconds. There are no noises like rattling like the cam adjuster issue, so I'm not sure if it would be that. I've been getting codes for knock in several cylinders but that seems to have gone away after changing spark plugs. I monitored the live data at cold start and my short term fuel trim goes to -4% and then to zero after warming up. My long term fuel trim is always at 6-8%. My bank 2 o2 sensor says it is at 32% and my bank one o2 sensor is at 0%. Not sure what that could mean. I think the motor is running rich when cold or something because there is fuel in the oil after about 5000 miles on the new oil.

I'm thinking maybe this issue could be fuel related, pcv is clogged, or maybe the cam adjusters timing really is off? I'm not sure. Anyone have advice?

chassis

Injectors on their way out?

O2 sensor(s) on its(their) way out?

Coils?

mercjames

Hopefully not injectors, I hope its something simple. Car has no codes other than the codes for knock in cylinders 2 and 4, which never came back after clearing the system. I've changed the spark plugs and made sure they were at the correct gap. Coils and o2 sensors aren't throwing any codes but o2 sensors trim seemed odd. I've checked for vacuum leaks but found nothing.

This issue is really weird because it seems to only occur during open loop at cold start. Once open loop closes, everything is ok. I don't think the car even uses the o2 sensors during open loop. What other things are not used during open loop? Cam magnets? Since the cam adjusters have a locking pin to hold a default position until oil pressure builds or when the motor is shut down. I've also heard the high pressure fuel pumps on these motors can give trouble, so could also be that.

I got an extended warranty notice from MB about the cam phasers for up to 120k miles or 2 more years. I may get Mercedes to diagnose the issue as they said the diagnosis is free if they find that the cam phasers are the issue.

Odd Piggy

My 2013 C250 began hard starting at around 75,000 miles. It ran poorly for about 30 - 45 seconds on the first morning start. After that, it started and ran fine for the rest of the day. I changed spark plugs with no improvement. There was no CEL and there were no codes. A MB courtesy check (no diagnosis) found no notable problems. I drove it for about 4 months more. Then the starting became noticeably harder, cranking for about 15 seconds before firing and running really rough for up to a minute. The complete diagnosis showed that one of the cam adjusters had failed. They replaced both cam adjusters and the timing chain. It took about 2 days for the repair and the car runs like new. MB covered the entire cost. The mechanic said that hard starting with no CEL is the first sign of the problem. I suggest that you insist on a complete diagnosis, understanding, of course, that if it's something like the fuel rail pressure regulator, you'll have to foot the bill.

mercjames

Thanks for the info. This seems like my issue as I have no engine light or codes..yet and the engine runs terrible at cold start. I'll be setting up an appointment to get my car diagnosed and I hope this really is the problem because it will be free then!

Also I've been doing some reading on the forums and it looks like my pcv valve may be junked too. I'm getting some fuel in the oil. Fuel contamination I'm sure doesn't help the cams..may be replacing the whole pcv hose mess (seriously who designed the pcv) under the intake as well.

Odd Piggy

Your oil dilution issue could be something in the fuel delivery system, too. My fuel rail pressure sensor failed, the gas mileage got noticeably worse, and the oil diluted to the point where it showed over full. I don't think that's what killed the cam adjuster because of the time lapse.

I have a well equipped home garage, but there are some things I just don't want to tackle, and my diagnosis ability is limited to a mid-range Autel scanner. The diagnostic units the dealer has are far better.

FYI, all MB service departments are not created equal. If you have a choice, choose one that has the "panorama" view waiting room, where you can observe them diagnosing and servicing your car. Maybe it's just me, but I feel more comfortable that way.

mercjames

Have you had your high pressure pump fail? I may replace the fuel pressure sensor too if I remove the intake. May clean up the intake valves as well and possibly figure out how to put a catch can on the pcv. Looks like the pcv system has two parts to the pcv? The main ventilation being built into the valve cover and then everything is sent upstream of the turbo from the large pcv hose. I'm assuming the brake booster vacuum pump supplies most of the engine vacuum. Then there is the partial load vent under the intake with the cyclone oil separator. Haven't looked at it any further but it may only be possible to add the catch can at the large main vent tube.

I'm decently equipped tool-wise too but I'm sure the dealer has several specialty tools. I wanted an Autel but they can be pricey. I went with the Carly scanner and their app subscription for Mercedes since it was only $70 for the scanner plus the $20 annual subscription. It seems to read most of the car's modules.

My Mercedes dealer here has the waiting room completely closed off from the service area, so unfortunately I can't watch my car like I want to. The times I have brought the car there I sometimes will just ask to talk to the technician and they usually let me. So I get to see what they are doing back there. Techs don't seem to mind really.

chassis

Yes cam timing seems like a possibility. An easy check is to swap cam position sensors and see if there is a change. Also, remove the cam position sensor connector and look carefully into the connector body with a bright light, and see if any oil seepage is present. This can lead to CEL and misfire. Oil seepage in the harness is a somewhat common Mercedes "feature".

Odd Piggy

My high pressure pump has not failed. In 20 years of owning Mercedes I have had only one failure like that. I'm pretty good friends with 2 indie mechs who both say that fuel rail pressure sensor failure is a rather unusual. But if you're in there, it may not be a bad idea to change it. The PCV system seems a bit over complicated, but I suppose that's because this engine has "grown up" from earlier, older versions. This is also my only turbo car. Still, this car is far less maintenance than my grandson's twin turbo Bimmer.

CHASSIS has 2 quick and easy checks to make that I'll catalog for future reference.

mercjames

Thanks for the info chassis and odd piggy. Very much appreciated. I’ll have to try the tests you suggested chassis as I haven’t tried anything like that.

Agreed odd piggy that twin turbo bmws are troublesome. I almost picked up a n55 335i instead of this car but decided not to.

Odd Piggy

Good luck! I think the W204 C250 is a good compromise between utility, economy, and decent performance & reliability.
That E93 Cabriolet N54 was fun to drive, fast, impractical, and a money pit.

ezshift5

Agree with you Piggy. Especially vis-a-vis economy - - - - an unexpected plus for this beautiful little coupe.

Holiday's best,


ez

chinatownabc

hey were you ever able to figure the issue seems my c250 is doing the exact same thing. Thanks

mercjames

The issue seems to have gone away for me, I think I got bad gas to be honest. No codes in the system since then. My car always runs better once it is out of the warm-up cycle, I don't notice anything during warm-up anymore that would seem out of the ordinary for any car. The injection noise is slightly louder at cold start and the car has a slight vibration due to the extra gas it's pumping in to warm it up. But it does not shake violently. If your car is shaking a lot or is hard to crank over then I would check your car's codes with a good scanner. Only thing I can think of that might not throw a code would be the pcv hose that tends to break on the intake. People have said their car runs like crap when that breaks and they don't always get a code. It could also be the timing chain issue known on these cars but if that gets worse you will usually get a timing code sooner or later. Anything else like ignition coils, spark plugs, bad high pressure fuel pump, etc will usually throw a code pretty quickly, but not always a check engine light.

chinatownabc

thanks. I didnt have this issue before a high pressure fuel pump recall. I had it fixed at the local dealership and now I have this issue on morning startup and shows I have misfire on all 4 cylinders. They already change spark plugs and no help.