Some time last fall my car developed a slight hesitation at about 4200-4500rpm under full throttle acceleration. There was no CE light, and no other symptoms.

The dealer diagnosed it as mis-fire and replaced the plugs, announcing it cured. It was not. They refused further diagnosis, claiming it fixed. I kinda forgot about it, as it's quite slight, and I rarely call on the car hard enough to feel it. Well, I'm kinda tired of it now, and it's begun to nag away at me. I am going to try to solve it myself since my warranty is now up.

The car drives and runs perfectly otherwise, and has not had a CE light. Fuel economy is spot on, no oil usage, nothing out of the ordinary.

Here's my thinking...

1. Fuel filter, or fuel pump? Maybe a fuel pressure regulator?

2. Misfire? I have my doubts about this one, as there is no CE light, but you never now. Plugs are only a few months old, but...

Once it clears the "rpm zone" it pulls pretty cleanly to redline and shifts perfectly.

Also, it seems like if I slightly let up on the throttle, it clears the "rpm zone" better than if the pedal is depressed to the floor. I'm not sure if the M111 has two fuel pumps, but this condition makes think if so, one might not be keeping up.

Help!

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John Shellenberg
1998 C230 "Black Betty" 240K

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