I had some plastic fuel lines and o-ring seals replaced several months ago after experiencing significant fuel leaking from the pump. Ever since I got it back, I have noticed what I would call a "hesitation" or hiccup in acceleration on changes to accelerator position.

It's much more pronounced at higher engine rpm's- for instance, if I am driving along the highway at steady 65 or so, if I gently release accelerator pressure and slow down a little, if I then depress the accelerator pedal to speed back up, I will notice a momentary stumble or hiccup before the car actually produces power. This is also very pronounced if I keep the transmission in 2nd gear and run the car up to a steady 3,000-3,500 or so rpm, reduce the power momentarily, then increase power.

It is definitely NOT turbo boost/lag related, and feels much more like a fuel delivery issue. I have also noticed a drop of a couple MPG as well as possibly a little more exhaust smoke under heavy acceleration- (not at idle) *NOTE that ALL of this has only been a problem since AFTER the dealer did this work on the pump and fuel lines!! I also think the engine sounds alot more "diesel like" than it ever has...much more nailing/clatter sound.

On the invoice, it also said they set the pump timing (which I NEVER told them to touch!!)

Could this be timing related, or perhaps did they introduce some contamination into the fuel system with the pump lines off, and I now have something partially clogging an injector or two?

I have not tried to use the diesel fuel purge as there doesn't seem to be a "cigar hose" to introduce it into the fuel system (maybe hidden under the intake manifold??) (much easier in the old 240D!!)

ANY help would be most appreciated!!

J.G.

Jay, with the hood open look for air bubbles in the clear lines. Rev the engine by hand as the throttle cable is on the right. That is a solid start. Air in the fuel system in these things causes all types in interesting scenarios

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#dieselFLEET
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'97 E300
'99 E300

I checked the "clear" fuel lines...no air bubbles as far as I can see.

Still have several old "brown" plastic lines in there that I can't see in too clearly...(I had INSISTED that the dealer replace them ALL when they fixed the fuel leak- so as to avoid pulling the intake manifold at a later date when the NEXT one fails) They DID NOT replace them all, and I complained. They said "I guess the technician felt the rest looked ok." so much for listening to the customer!

Could give you an EARFUL about my exploits with this STEALERSHIP!!!

Any other things you'd recommend I can check??

I had a similar condition which I noticed went away after replacing the main fuel filter. I also had done some other work on the fuel system as well but I think it was related to the filter mostly...how long has it been since you replaced it?

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Good point! Forgot about that

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#dieselFLEET
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'97 E300
'99 E300

The fuel filters have been replaced within the last year...however-

I've been searching through posts for similar fuel related problems and came across leaking fuel shutoff valve as a potential problem...

I definitely don't have any more leaking fuel (that I can see or smell) however every 5 or so shut downs, I have noticed that the engine is slow to shut off. Once it even took me putting the car in gear to get it to shut off. (That time it set a code in the ECM for something about shutoff valve problem) I cleared the codes and it hasn't set again, but I still have occasional slow or delayed shutdown.

Is this a possible contributory factor??

J.G.

It's tough to say, but if you haven't had it replaced... Don't waste any time. These fuel system is run by all sorts of electronics, so imagine, if one little electrical item starts going it through's off EVERYTHING.... I would also change the main fuel filter just for giggles.

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#dieselFLEET
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'97 E300
'99 E300

Looks like I've got some work to do this weekend! I suppose a new fuel filter never can hurt either...

Thanks.

J.G.

Yes. Replace that valve.