I've been experience episodic power loss on my 1984 300TD (OM617), which I bought in January. It's my first car and I'm a new mechanic, so bear with me...

The problem:
First occurred when driving cross-country, going 70mpg on interstate in Iowa. Car slowly lost power (full throttle, slowing down gradually). I changed both primary and secondary fuel filters. Nothing happened for another 1200 miles until I was back in New Hampshire. Since then (the last 9 months), every couple of weeks I lose power... usually after about an hour of driving, or when going ~60mph on interstate, or going uphill, or on a low tank... but not always. I've also lost power right after starting the car up in the morning, or when slowing down coming off the interstate, or on a full tank... so no consistency. Usually I keep driving and start going downhill and pick up power again, or in worst cases the car will completely stall, but start up and run fine again after 'resting' for a few minutes. For a while I just drove it and let it rest since I couldn't figure out the problem.

Recently the problem got worse, and about a month ago I took out the filter screen at the bottom of the tank. It was gunked up and I replaced. Problem continued (no better), so I just checked the fuel screen again, expecting it to be clogged and planning to remove the fuel tank and clean it. The fuel screen is totally clean (see photo), so I'm not sure what to do next.

I double checked the fuel lines all the way from tank to fuel filters (I replaced sections of these back in January), and don't see any leaks or kinks.

My question:
Where should I start looking next? I was considering a diesel purge to get the injection pump and injectors cleaned, but it seems unlikely that this is the problem (I will do it eventually anyway). Do I have a faulty injection pump or lift pump? My air filter could be changed, but it was totally clean when this first started happening so I doubt that's the problem.

Other things I've done with this car:
new tires, exhaust pipe, coolant bypass hose, rear trailing arm replacement, valve adjustment, manual heater motor blower switch (CCU not working), bypassed auxiliary coolant pump... none of these should have anything do to with the problem. Car seems to run at pretty normal/consistent temp (80-90deg).

I'm hoping from the lengthy description above you all might have some insight (key feature: episodic, sporadic, gets better after 'rest'...usually, gradually getting worse), but I'm happy to tell you more.

Thanks so much!


See attached photo of screen tank filter I took out and checked today (totally clean - came out of the car like this), and the one I replaced about a month ago (dirty).

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