recently, while accellerating, my 240D exhibits a 'squealing' noise coming from somewhere underneath the car. also, i've noticed that the car cannot keep speed on the highway, and falls in speed after 5-10 minutes of driving on the highway. is this a fuel line problem, or something else?

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1980 240D, 197580 miles - "The Stuttgart Stomper"

Check your belt tension. The power problem could be a fuel issue...have you changed the fuel filters?

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

yes both primary and secondary filters have been changed.

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1980 240D, 197580 miles - "The Stuttgart Stomper"

Walk around and make sure your wheels are all about the same temperature next time you have your car out for a run. This is just in in case you have a dragging brake problem. It might also squeel or a simular sound when first underway.
Costs nothing to check and it is just a thought but might explain the two symptoms at the same time. Get a friend and see if car pushes pretty easy on flat road by hand as well is another test for brake drag. I do not really suspect it is the problem but just wise to eliminate it as a possibility.

yup, old glazed belts or incorrect tension will cause squeeling, also an alternator w/ failing bearings, or ps pump.

if your car is losing power and the filters have been changed (was the pre filter gunky?) it might be the tank strainer, or possibly a very small air leak

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Cheers,
Robert

Check you accessory belt for glazing. Try sanding them with some 200 grit sandpaper and see if the squeal stops. Or try a belt dressing If this does it AND the tension is normal then replace the belts.

Acceleration. Did the prefilter have any indications of algae or fungus. A black tint to the fuel. It should be a golden color. If so the fuel tank screen is probably blocked. Do a search on "algae" and "fungus".
To see if it is the in tank screen being blocked, disconnect the inline filter and blow some air back through the steel line to the tank. That should blow away any crud around the screen. Remove the tank filler cap before blowing the air. Now go drive the car and see if the top speed is limited. If this corrects the problem then you need to clean the screen in the tank.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car