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1982 Mercedes Benz 240 D- Lagging at high speeds

Recently I’ve noticed that when I take my car up to highway speeds- 55 MPH or higher- the engine feels as though it hesitates- I don’t actually slow down, but I have trouble accelerating beyond where it starts to lag. It’s like an imaginary bump my car is going over where the engine isn’t fully accelerating. Happens for a second, then goes away, but lately it’s happening often- several times in a row- it just feels laggy, sometimes continuously, and i’ve got a bad feeling about it.
Tires and brakes are completely new (Nov 2011, calipers, rotors, and pads replaced), oil level is checked weekly and has been fine lately. ~200k miles. It’s a manual/ 4spd, I don’t know if this is clutch/ transmission slippage, or if I have a piston misfiring, OR if maybe it’s a fuel injection problem- Any ideas?

In this picture of a 240D engine you can see a black hose passing from the first fuel injector to the second. Then another black hose goes from #2 to #3, and another from #3 to #4. On the nipple of #4 that would be where the hose would go to #5, if you had a 300D, there is a little plug. I think what you are saying is exactly what is caused when that little plug is no longer plugging its hole. The plugs are available in five-packs from your friendly local Benz dealer. I doubt you could explain it to a computer puncher at Autozone. You probably should have a new one on hand before you pull it off and see if it’s deteriorated or hardened.

After 30 years and 200K miles, you can expect to lose a little top end snap…Fantasy and reality have to be reconciled at this point…

Just a wild guess but it sounds like a fuel starvation problem. Might want to look for an air leak in the fuel line. VWs don’t have one but I don’t know if a Benz diesel has a booster pump in the tank which would make a fuel line leak apparent.

Check your fuel filters as well, those cars are very suseptible to water build up, and crud build up. If the fuel pressure is off so will the power.

You may want to google for a specific 240D forum. These durable simple cars seem to have some serious longevity and owners willing/able to DIY.

gsragtop Quote: “Check your fuel filters as well,” Unquote

I thought of mentioning that too but the power loss problem is momentary. Wouldn’t a plugged fuel filter prevent the car from accelerating beyond the speed where fuel starvation begins? I suppose anything is possible and a new fuel filter would eliminate that as a possible source of the problem. I have been driving a VW diesel for more than a few years; have opened up a few used fuel filters and have not seen one that was even remotely close to being plugged.

Quoting @Caddyman After 30 years and 200K miles, you can expect to lose a little top end snap…

Of course you’re right, but you also have to remember that a 240D never did have any top end snap. I had three of 'em way back.

When I was a kid, we had a 1970 220D. I think it was rated at about 60 horsepower. It had 4 glow plugs in the engine and one on the dash (yes, a real glow plug cover with a protective heat shield). When the plug on the dash glowed, you could assume the ones in the engine were as well. When it glowed, you pulled the starter cable out even further and the starter would crank. Quite an ordeal to start a 2.2 liter 4 cylinder engine. It was extremely powerless but its longevity was incredible.

@kawasaga The early 240Ds and other Benz diesels used the same system. I had to pre-glow my first one for a minute before I could expect it to light up on a 10°F day. My last one had an improved system that was supposed to be ready to go in under 10 seconds. Usually it worked.