Just drove the 99 E300 with the low MPGs from SF to Colorado - still in the range of 23-29 mpg on the highway, but also noticed some really interesting behavior that cemented my opinion that there are issues with injectors and/or the fuel controller:

At high altitude, the car started making really strong clattering noises for several seconds each time I released the accelerator at low RPMs.

And, crossing Vail Pass (10,000'), the car was smoking (white smoke out the exhaust) like crazy between 2000-3000 rpm (and also surging a bit); dropping it into 4th gear and keeping the revs up got rid of the smoke.

So, the injectors are clearly dumping too much fuel. Two questions:

1) Does the 99 E300 have any altitude compensation (and/or is this "normal" behavior)?

2) The car is under warranty, so I'm going to take it in to have work done - anything I should specifically look/ask for? (I stopped at the dealer in Denver and they said that they suspected a "dripping injector" but that they had to open up the engine and look, and it would take 3-4 days for them to take care of this including ordering parts).

Thanks...

Yeah, that's definately way low. My '98 E300 was always returned right around 32MPG on road trips. Plus or minus 1MPG was about all it ever varied. Never dropped into the 20s, but I never got the rated 34 either.

These cars suffer from Air Mass Meter failure just like the gasoline cars. I'd suspect the AMM. It has a strong influence on the amount of fuel injected. But frequently it also causes a low power condition as well.

I guess it could be injectors, but typically they are very robust. One just doesn't hear of injector problems before the car has a couple of hundred thousand miles on it. Worth a look as it's not that difficult to pull and test them.

My $.02,

- JimY

Good point - I'll mention the MAF sensor as well then I talk to the dealer.

If it was a faulty MAF wouldn't the CEL light come on to indicate MAF malfunction?

I also have a 99 E300 TD with 93K mi and the milage is 26-28 mpg and I am at sea level. I had CEL light for MAF but after I cleared it it has not come back. I though maybe there was some fuel leak.

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2010 ML350 Bluetec
2012 Mustang Convertible

Rafi, how did you clear the CEL? Did you disconnect the battery for a few seconds? I do that on the ML I own and its taken care of most of the CELs so far. They don't come back for months. I drove my E300 to Rocky Mt National Park at or above 10,000 ft and it did the same thing when taking my foot off the accelerator. A loud clattering could be heard until the rpm was at idle. When I came back to sea level she worked fine again. I know there is altitude compensation on the 606 engine....it is also on the turbo version of the 617. I remember taking my 83 300D up to the mountains around Denver a few times. No comparison however, the 300D was a bit of a dog up there and the E300 is still strong once the tubo is online.

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99 E300 133K
98 ML320 99K
87 Saab 900 Turbo Conv 123K

If your alda is bad, it will cause this problem. I had the same thing happen to my S350 in Colorado a couple of years ago and it was the alda. It worked fine on the pressure side, but before boost builds at high altitudes it would not reduce the fuel. Unfortunately, you will have to remove the injection pump and sent it to a qualified Bosch repair shop to know for sure. Unless you regularly drive at high altitudes, I would not worry about it.

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1995 S-350
370K + SOLD
1952 220B Cabriolet
39K kilometers + SOLD
1998 E300D
310K +
2012 E350 BlueTec
120K

Ockman - I cleared the CEL with Snap On scanner that I borrowed.

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2010 ML350 Bluetec
2012 Mustang Convertible