I have a Mercedes 83 300 DT that has lost almost all power. It will start only with the accelerator on the floor and is hard to start. It ran fine and set up for maybe a week and a half and suddenly lost most all power. I replaced the primer pump which was leaking but that had no effect. I bypassed the new primer pump with a bulb from an Elsbett kit which primes the fuel line quickly still no change. I pulled a vacuum on the fuel line and it dropped maybe 3 inches in 10 minutes. Is this normal? I am planning on replacing the tank strainer but question if that will do any good since fuel seemed to flow easily into the primer bulb.
I have replaced all of the fuel lines with mostly new clamps. I have not cleaned the banjo bolt yet but plan on doing that as well.
Any further ideas? One thing I noticed was that for a while when first started that it again had very little power but perked up quickly once warm.
Thanks

Have you changed out the two filters in the engine compartment ?
Have you put more fuel into the tank to make sure algae and stuff has not caused the strainer there to stop the normal flow ?

Try swapping the in and out line from fuel tank to filters as the tank screen might be clogged.

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I have replaced the two fuel filters under the hood and all of the fuel lines except the clear line going from the spin on filter to the IP. That one does not appear to be leaking, there is no fuel dripping from the top or bottom connection. I will try switching the lines on Friday.

It ended up being the fuel injection pump, lucky me. I got a used one installed to the tune of $1000. Took a year to find the right mechanic and for him to find a pump he was comfortable with. He tested the pump by moving turning the screw on the injection pump that controls the shaking (I forget its name). He noticed that it had no effect on the pump. I think the real clue was that it happened so quickly. The engine ran fine and then didn't.

WOW great upkeep on the thread! thanks for finishing it!
posting here more often could have gotten you an IP from one of us a tad quicker...