Power problem: loss of, what else?

diesel
mercedes-benz

#1

320 k miles! Rear driver’s side panel has rust, but otherwise fine for a pre-cup-holder/pre-CD vehicle. Inherited from my dad. A connection to the past. It costs me more to garage the car in Manhattan than many pay to lease their car new.

Car is Dr Jekell till, without notice, perhaps 100 - 150 miles into drive, morphs into Mr Hyde: loses power on hills. Even mild grades reduces speed significantly. Car will drop down to 45 mph on interstates in hills. Can feel a mild “bucking,” as if timing or fuel or air is being interfered with. A real killjoy for my driving experience. My MB dealer is not a franchise. These are real MB mechanics, yet they have only been able to work around the problem by improving other factors of performance lost by age. They do not have a Dx but I believe they are honorable and competent. Everyone is scratching their heads. But my wife is about to go after me with rolled up newspaper, demanding a new car.


#2

I don’t know 1991 diesels well, but I would be thinking about a limp mode of some kind or the turbo is not coming on when it should. Overall they were good solid cars, and I suspect once the problem is found, it will be good for another 300,000.


#3

“Limp Mode,” I am blind sided. What is it?

Thanks,
Hank


#4

I just looked up the definition online. I see 2 aspects. The first is a sensor failure leading to a “self-correction” that the program uses to address the perceived issue so you can “limp” home. The second might be specific to the example, in that it deals with restricting the transmission to one gear. (This is an auto transmission) But in my situation, only the first applies. The power/speed drops till it goes into passing gear, then it drops precipitously. I am assuming the Limp Mode problem is not addressing the transmission specifically in my case, but perhaps the fuel/air mixture? As a diesel, I didn’t think timing is ever problem as ignition is with compression, not spark. Does this sound plausible to you?

Thanks,
Hank