Friend is having a baffling problem with a 1999 E300d. Car has a pretty pronounced knock/nailing sound at idle that immediately disappears when throttle is applied, load or not. It is also smoking pretty bad, (black smoke), under any kind of load.

Injectors have been changed with new Bosch. No difference. He is about to send out the pump for rebuild to Pacific but before he does this, I thought I'd ask about this here. It is running like it's getting way too much fuel. How is the ALDA compensator utilized on these engines? I'm thinking that it's electronic, (as opposed to the atmospheric(?) one on my OM603. When I got my OM603, the PO had completely removed the ALDA compensator and the car ran really rich.

Thanks a lot as always.

Might the sound be a bad belt tensioner damper? Put pressure on the damper upper attachment - press downward and pry it away from the head. See if that reduces or changes the knocking noise.

Loosen eash injector line with the engine running to see if you can isolate the noise to a cylinder. Then swap injectors to see if the noise moves with the injector or stays with the cylinder.

A mechanical ALDA has no effect on idle.

Sixto
87 300D

What is the mileage on it?

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Jim

Does it knock when warm at idle or just when the engine is cold?

I just solved my nail/knock recently with help here, turned out to be the fuel shut off valve. Mine had been knocking while cold for a few months, then it starting leaking diesel which helped me solve the problem.

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1999 E300 TD 190,000
1996 Passat TDI 225,000-sold
1996 E300 120,000-sold
1998 Jetta TDI 186,000 -sold
1983 Chev Suburban C20 6.2-sold