I have a 1991 300E with the 3.0L M103 engine. I've been driving it for the better part of a year, and it has been painfully sluggish, especially below 3000 rpm. It hesitates badly off the line, and labors to maintain speed, even around town. I'd accepted that this was normal, but after having a mechanic replace the air filter, plastic intake hose, and fuel pressure regulator (which happened to be leaking), it ran brilliantly for just a few days. Completely smooth and competent, even quick.

Now, it's driving like it had been before, slow and unresponsive to throttle. What could possibly be causing the problem?

Incidentally, the problem seemed to return about when I filled up the tank. I would be inclined to think this is a coincidence, though, because I filled it up with Shell V-Power at the station I usually go to, and the gas I have bought there has not caused any problems with any of the other cars I drive. I have never put anything but name-brand premium gasoline in the car.

*Edit* I should probably add that I replaced spark plugs and wires not long ago. I don't know how old the cap and rotor are.

I was able to eliminate hesitation off the line by readjusting the static fuel mixture on my 88 300SEL(requires a an exhaust analyzer). Your problem seems different as it went away after some repairs and then returned. It could be trash in the fuel tank.

Lenny

p.rex, definitely inspect the distributor cap and rotor. Check when the fuel filter was replaced last. Fuel filters should be replaced every 60,000 miles on the 124 cars. You didn't mention why the mechanic worked on your 300E, but if he is a knowledgeable MB-trained tech he should be able to diagnose the cause of the sluggish performance.

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Fred Hoelzle

Boy, I hate to sound like a broken record - but it will more than likely be an ethanol related issue.

We are seeing major breakdown in the fuel systems due to this new blend of fuel.



Luther

I dunno, Luther. I think that is a pretty bold diagnosis considering you've never seen this guy's car.

Granted fuel sucks these days, but if you read the owner's manual, the car was designed to handle 10% ethanol.

My 103 doesn't mind crappy 92 octane fuel with 10% ethanol. Why should his?


-tp

Here's a couple of quick and easy things to check.

1) Is the air meter plate moving freely?
2) Is there a lot of slop in your accelerator linkage and dried out grease?
3) Have you done a fuel pressure test?
4) Have you ruled out vacuum leaks?
5) Have you checked your temperature sensors?
6) Is there soot in your tailpipe or other evidence of running rich?
7) Are there any carbon tracks or other signs of coil deterioration?

What do the plugs look like when you pull them out?

Those are some good easy things to check. If you aren't sure how to do those things, please ask!

-tp

p.rex, presumably you didn't install platinum spark plugs. Those are a no-no for 103 engines which need non-resistor, copper electrode spark plugs. Refer to your Owner's Manual.

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Fred Hoelzle

Is the plugs restriction due to "R" type ignition leads ?
non resistor plugs are a rare availability.If the leads can be converted to standard and use the quad electrode bosch plugs ?
regards
mak