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1990 740 Turbo, buzzing fuel pump

Since a few days the fuel pump that is located in a little cage under the car together with a fuel filter started making a buzzing sound.

I did notice as well that one of the clamps attaching the fuel line coming from the tank is broken as well but holding it does not seem to stop the noise.

The car drives normally (=good) and I cannot notice any difference in fuel consumption?

Any ideas about the cause? Are these pumps subject to failure (the mileage is 180500 miles)? My mechanic seems to suggest the primary pump in the tank might be defective, any similar experiences?

Philip

Philip Leduc

actual brick

90 740 Turbo sedan
Reply to
Philip Leduc
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assuming it's about the same as the fuel system on my '89 240, I'd say your mechanic is probably right! If the in-tank pump fails to deliver fuel to the other pump, it has to work harder. Another source of failure is the rubber coupling between the in-tank pump and the outflow line. However, if you have to pull the pump out, you might as well replace both at the same time! Until then, I've read that keeping the tank more than half-full helps.....

Reply to
Frank Furter

Very common, and probably correct diagnosis. If the delivery to the main pump is choked, then the fuel may cavitate in the line to the pump input. The pump pumping this vapour-liquid is the noise you hear.

Reply to
Mike F

Make sure your primary pump "the one in the tank is working "as it overload the main pump which has to pull too hard . If your mileage is up high may be better to replace both and bite the bullet as most times the strain ruins one or both pumps as well the fuses to the pumps melt the connections .

Reply to
John Robertson

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