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Old 12-05-2001, 02:55 AM
Human Spirit
Join Date: Nov 2001
Location: Minnesota
Posts: 56
Question Rich Fuel Mixture, Poor Fuel Mileage - after front end collision - '90 300E

Perplexed in Minneapolis . . .

BACKGROUND: In June, 2001, my '90 300E with 145,000 miles was running great, fuel mileage was 20-24 mpg. My daughter then ran into the rear bumper of a full sized van as she started out from a wait at a stop light. Van's bumper was high enough to miss our bumper but pushed in the grill and radiator, hood buckled about 6 inches, rt. front fender pushed back slightly.

Two months later, body repairs are complete ($6,900) but the body shop couldn't get the engine started. The vehicle was flat-bedded to local MB dealer. Dealer technician found no compression (believed to be from fuel washing down the cylinder walls) and worked hard to get started. Upon starting, engine ran rough. Dealer checked compression - OK Replaced fuel distributor block, somewhat improved. ($1,600) Drove vehicle home and in one week of driving, noticed a raw fuel smell from exhaust and fuel mileage was 12 mpg!

Returned vehicle to MB dealer. Checked air/fuel ratio and found engine running very rich. Lambda system could not get air/fuel ratio into specification - oxy sensor described as "lazy". Replaced Oxy sensor - no change. Ran a bottle of Techron through engine - no change. Dealer technician concluded: Need Valve Job!! - this conclusion I didn't understand. (Note: Technician noticed oil leaking externally from the head gasket but this has been happening for the last two years - nothing new - uses 1 qt. of oil every 1200 miles)

Took vehicle to another MB dealer for a second opinion. He confirmed the air/fuel ration was rich and the lambda system was unable to correct. He methodically checked all inputs and outputs to the computer/controller, checked and replaced the fuel injectors - no change, checked the fuel pressure regulator - O.K., found the EGR valve plugged in backwards (probably from re-assembling the right front fender at the body shop) - no change. Drove the vehicle another week - no change, fuel mileage still 12 mpg, raw fuel odor from exhaust still present.

The dealers are perplexed - any suggestions would be greatly appreciated. This was a great running vehicle and I would like to figure out this (relatively sudden) air/fuel ratio, poor fuel mileage problem.

Thanks and regards,

Wayne Lindholm
04 GMC Yukon XL Denali, Black, 12k
02 New Beetle, TDI, Reflex Silver, 24k
89 300TE, Arctic White, 214k

90 300E, 142k (sold)
87 300TD, 128k (sold)
83 300D, 314k (sold)
79 300TD, 266k (sold)

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Old 12-05-2001, 10:19 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Since the fuel pressure has been checked, I assume it is right.

If the pressure is right (and steady), the mixture is adjustable. If it is adjusted and isn't right in other conditions, I would expect an airflap misadjustment or a differential pressure problem.

Differential pressure is the venue of the fuel dist so that shouldn't be a problem. With proper testing your problem should be easy. I would be back to the one who sold you the distributor. I would expect a better analysis for what you have paid for.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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