1990 740 Turbo, buzzing fuel pump

[Philip Leduc]

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

 

[Frank Furter]

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.....

 

[Mike F]

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

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.

--
Mike F.
Thornhill (near Toronto), Ont.

NOTE: new address!!
Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

 

[John Robertson]

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 .