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2005 E320 CDI engine misfire at idle when fully warm

683 Views 14 Replies 4 Participants Last post by  DieselBound
I have been pulling my hair out trying to solve this problem. Several months ago I noticed my car would sometimes stumble at idle after a long day of driving. It would only happen for a moment or two and it would smooth out. But as the weeks passed, the problem would happen more frequently with less driving, and eventually turned into a full blown misfire at idle. However the problem only happens at idle when the engine is FULLY warmed. If I let the car sit for a few hours and go to start it, the engine purs just fine....until it warms up again. And it only happens purely at idle and when I let my foot off the accelerator. Any throttle at all and the engine totally smooths out and works perfectly fine.

I have tried replacing the injector nozzles, seals, and return line o-rings with no change to the problem whatsoever. I just got done doing a leak off test and all the fuel levels were dead nuts even with each other.

I have replaced the fuel filter, bypassed the EGR valve, and I have all but deleted the swirl flaps. Nothing has even made a change.

I have taken this car to a mercedes shop to see if there were any hidden codes, and with the exception of the egr being bypassed, there are no codes for fuel pressure.

I honestly have no idea where to go from here. I would appreciate any insight you guys might have.
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No codes for fuel pressure but how about other codes?

05 E320 wagon 189K miles
Nothing. The most I have is a code for some lightbulbs in the trunk that need to be replaced.
Been a long time. Update:

I finally had all my injectors refurbished by dynomite diesel. They flowed them, matched them, and everything came back good. I just got done installing them and fired up the engine. Fired right up.

This time I have a fancy autel scan tool that I had hooked up and was watching all the live data.

The moment the engine hit 60C on the scan tool, the engine made a sound up near the belts as if the ECU changed something. Not even a half second later, the loud knocking and misfire was back. Same exact thing. I can push on the throttle and it smooths right out. I am completely stumped.

Scan tool says rail pressure is good. The only thing it doesn't like is the fact that the injected quantity is low sitting at 3mm vs 5-7mm.

I replaced the quantity control valve with one from a working car. This made a significant improvement, but the problem wasn't fully fixed. I drove the car some 1600 miles on a trip down to vegas and back, and the problem seemed to be a tiny bit better. I couldn't quite tell if the car was better or if I had just gotten used to the problem.

This morning I was fiddling with the swirl flap lever arm and wired it open. When I left the house I noticed I had no turbo and very little power, but the idle issue was totally gone! When I got to my next stop, I cut the wire holding the valve open expecting the idle issue to come back. The issue did not come back, but I still had no turbo.

I got home and looked for codes and I had a 2513-1 code. I cleared the code and I had boost again, but the idle issue did not return either.

I have no clue what fixed the issue or if the issue will soon return, but hopefully the car is happy now.
How did you "bypass" the EGR valve?

Seems fairly predictable in which case this shouldn't take much to track down.
I just unplugged the EGR valve and erased the codes for a few test drives to see if it made a difference. Since then, I have plugged it back in.
Does it start regen attempt then?
I do not believe the OM648s have a DPF filter and therefore the car should not have done a regen. I am pretty sure DPF started with the OM642, but I could be wrong.
Correct, no DPF.

So... are you still witnessing the sounds up front when hitting 60C?

EGR functions are temperature-based. I don't know about the MB (I'm new), but I do know that my VW TDIs (ALH engines) deactivate the EGR valve around this temp.

Regarding the swirl flaps, manipulating them manually might have exercised them enough to free them up, a bit: I don't trust any of this stuff which is why I am installing a manifold w/o flaps (I can readily do this because I have my engine out). Intake flow patterns fluctuate as these flaps operate; supposedly they're supposed to be of most benefit at lower RPMs (likely to affect idle). I don't know if the ECU, in regards to triggering an error code, is able to fully track proper operation of the swirl flaps, whether it's a "it works or it doesn't" sort of thing vs a "it's only working x%".
Nope. Lumpy idle is totally gone at all temps for the time being. Hopefully things will continue.

And yeah, I hear you on the EGR and flaps. I am going to be deleting everything I can on this car going forward.
Well, my W211 OM648 had DPF, but it was a initially sold for German markets.

Check what your back pressure sensor reads when problems start. That is very common source of gremlins in OM642. Overall, it could be wise to try any angine live data when it starts misbehave. Problem is little bit chicken - egg dilemma, when some reading jumps, is it culprit or result... Good luck!
Interesting. I will take a look for one on my car just in case. If I have one, that would certainly explain a lot.
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