vibrating noise help, havent a clue what it is

[benjaminamoo]

i have a 1990 316, started it up yesterday morning and really loud vibrating noise started coming from the back end, it makes the noise constantly as long as the engine is switched on and cant be the exhaust because the sound doesnt change when im driving it, so im assuming it must be something electric?

any help would be appreciated, im fairly new to these cars, only had it about a month thus why im clueless

Ben

[aimlessrock]

Ben, i assume this noise has been present since you acquired the vehicle?..what about idling?..does the noise persist?

not sure how you have ascertained its an electrical issue, vibration is usual mechanical i.e propshaft, diff or possibly suspension.

Need more info.

If your not mechanically minded and concerned i would get this checked out now for safety reasons.

[Billwill]

Noisy fuel pump maybe?
Exhaust hitting on the underbody somewhere?
As stated above is the noise there while at idle and stationary?

[Brianmoooore]

Nothing like enough info. to give anything like a firm diagnosis, but a fuel pump that suddenly becomes noisy is usually because the commutator in the pump motor has worn completely away in one place, right through the copper to the plastic. The pump will deteriorate rapidly in this state, refusing to start unless hit, and eventually refusing to run at all.
To check, remove the bulkhead wiring cover, pull out the orange fuel pump relay, and short together pins 30 and 87 of its socket. This will make the pump run without the engine, so if it makes the noise then, this is your problem.
Another possibility is a heat shield that has fallen down onto the exhaust.

[benjaminamoo]

thanks for the response lads.

the noise is constant as long as the engine is turned on, it does it all the time whether stationary or moving and the sound doesnt change at all. i think fuel pump is the best bet as to what it is, however its only just started.

will this be why my engine idle's so badly when cold aswel? because the pump isnt functioning properly?

also, estimated price to replace the fuel pump if this is the case?

[RedDead316i]

in regards to your cold idling problem thats more likely to be a throttle position sensor or maybe vacuum lines.