To try to solve this problem, I've replaced the lift pump ,the supply and return lines (tank vent is clear),removed and had the tank cleaned and both filters replaced . Over the past 7or 8 hundred miles, the car developed increasingly louder diesel knock(nailing?) especially around 40 but gradually knocking most of the time particularly on moderate accelleration . It's ok cruising at about 65 but gradually is knocking most of the time. Also, it will occasionally lose power when you transition from 1st to 2ed gear(manual trans). Sometimes just a little but sometimes almost down to nothing (like an interuption of the fuel supply) and it doesn't die. If you push in the clutch in and race the engine for a few seconds , you can drive normally until the next time it happens maybe even a few days. Several times when this first started I changed both filters and the problem went away for perhaps 100 miles. The intermitant nature of the problem is frustrating . Every time I do something to try to fix it , it seems to work for a short time. Any suggestions?

what brand primary filter did you use? many have noticed a small opening reduction of flow.
it REALLY sounds like low fuel pressure. perhaps your lift pump has the weak spring syndrome?
did you test fuel pressure? FUNOLA sells a kit to attach a fuel pressure gauge for testing...

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

You may have two problems. Sounds like it could have to me. You can keep doing this or that or install a ten dollar liquid filled 0-30 pound fuel pressure gauge to monitor what the fuel pressure is doing.

All 240ds especially should have one installed in my opinion anyways. But that is another subject. The pick up point for the gauge is between the output of the secondary fuel filter and the injection pump.

The only non gauge test I can think of is to shut off the fuel return from the injection pump. Still only provides limited information. This will not hurt anything and try the car for a day or two or until it acts up. This close off is only for testing purposes. Not to be permanent.

any particularly good gauges to go with?

Harbor freights 0-30 pound liquid dampened gauge is still probably around 10.00. What most have used.