Just drove a 91 350SDL . Zero to sixty took about 16/18 seconds. Thought these were suppossed to do this in about 12 seconds.
Also, did not seem to have a whole lot of power on a hard pull, going up a hill. Problems with injector pump timing ?
Also has a definite knock at idle, thought it might be a bad injector, goes away once rpm gets above fast idle. Any ideas ?

Sometimes just partially obstructed fuel filters. In fact low power is the typical indication enough fuel is not getting through. As for the knocking I just do not know.

Could be a few things. Might want to run Molly Lube injector cleaner through it.

Could be your kickdown switch, as the gas pedal. Mine was sort of stuck, prevening the car from shifting and accelerating properly. They also hit the fuel linkage with some lubing kind of stuff so it moved easier. The car was much quicker after this. Mine's a 1991 300d.

Make sure your air and fuel filters are good, so the car gets enough air and fuel to work properly.

Diesels knock. It's in a diesel's nature to make a knocking sound. clack clack clack!

But as for the lack of throttle, it would be worthwhile to check the throttle bushing. I had the exact same problem in my 240D, lack of throttle and power going up hills. Turned out the throttle bushing was worn out. Replaced it and it was fine.

As for the knock at idle-- try raising your idle speed slightly. Does the "knock" sound occur at even or uneven intervals?

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1982 240D 4spd, 327,000mi

Knock is very pronounced at idle. Even intervals .Sounds like one cylinder or rod is making noise, sound is "deep" in engine. Reminds me of a bad piston pin knock in sbc'sthat usually go away above idle .
Engine will rev well in low. Car had 120K on it.

I had one 350SDL, pulled apart a perfect-running engine and found that there was significant piston scuffing. The geometry of the 3.5L seems to be a problem, search "rod bender" to find out more, possibly a bent rod or breached head gasket (which could lead to a bent rod).

As far as power, search "switchover valve" and "overboost valve". There must be a clear path from the small vacuum/pressure valve on the top of the manifold to the ALDA on the IP for the car to get boost enrichment, without it you'll have much less power. Run the line from the manifold directly to the ALDA bypassing the switchover valve as a test, often the switchover valve gets plugged (clean with WD-40 or whatever) and sometimes the fitting on the manifold gets plugged (blow through, both should be clear).

Next be sure that the wastegate is hooked up, I've seen two with the linkage loose from the actuator.

Shift points are important, if the car can't get RPM it won't develop peak power.

Fuel and air filters. Without fuel, it will not develop peak power, without ample air it also won't develop peak power.

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Gone to the dark side

- Jeff