posted this on tech help but maybe you fellow dieseler's can help...
I have an 84 300TD and I have some issues with the fuel delivery system. I have replaced both fuel filters, injector bypass lines (they were leaking a lot) and the fuel lines in the engine bay and directly in front of the tank. I recently discovered the small (reserve?) tank behind the spare but have not replaced the lines to it. My car didnt have a fuel strainer in the tank. After issues with the primer pump on my fuel pump leaking a lot (now need new engine mount) I replaced that with an updated model. However, my car STILL runs out of fuel! It will be fine and I can drive for 10 miles or so at various speeds and then the thing just runs out of gas (diesel I know)! I have to get out and pump the primer pump for a while, usually til I can feel there is fuel in the lines again, and then I can 'usually' start the car right back up and go again for another 10 or so miles. When it does start back up, its just barely running and I have to pump the pedal a bit until it gets up to speed and then I can go. Im baffled. IP? fuel pump? Posted this problem on the other list with no help. Anyone ever hear of anything like this? I did buy a fuel pump vavle replacement kit, but havent had the guts to try installing it yet.
Help!

when it runs out of fuel, is the clear primary filter full or empty? (a small bubble at the top is ok)

when it runs out of fuel are you usually going up a hill?

I believe its sucking a small amount of air from somewhere, takes some time for it to kill the engine.

Is any part of the fuel system leaking at present?

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Cheers,
Robert

If the fuel line was leaking did you replace ALL of it or just patch it? If any of the original line is still on there chances are there is a pinhole leak that is sucking air, probably under a clamp or in some other hidden spot where you would never find it in a million years.

Running out of fuel this fast shouldn't happen. Have you checked to see if the tank is venting? Doesn't quite match what I experienced. Open that fuel cap and see if there is a strong vacuum? If so your vent is probably clogged

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My Daily : 96 E-300 Diesel with 195,000 miles
Retired: 92 300D 2.5 T 345K miles and for sale
Retired: 95 E320 157K miles and currently parked with blown engine

Both retired cars are for sale as is my w124 shop inventory

the prefilter still has fuel in it (with a small bubble). It doesn't really matter if Im going uphill or not, but it does seem to make it happen earlier if Im having to start from a full stop and accelerate or accelerate more to go up hill. I did completely replace the fuel lines (the rubber any way, not the steel) except for the lines I just discovered in the spare tire bay leading to the small (reserve?) tank that is behind the spare. There is evidence of some fuel leakge there. Plan on replacing those this weekend. I haven't messed with the fuel cap or vent, but will give that a shot. thanks!

This response sounds like a restiction to me. It is not unlike getting a fuel filter plugged. I would be checking for something plugging up the works, maybe reverse blow the fuel line with air.

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1977 300D Lost coolant while someone else was driving
1983 300D Can't run without oil
1985 300SD (gone but not forgotten)
1990 300TE 4matic Sold
1991 Yamaha Venture
1975 Kawsaki 250 triple
1974 Honda 200CL
1951 8N Ford
2008 Wildfire 650C