Fuel Pump Knock..

[tweedy998]

Hi all,

I'm getting an occasional knock / tapping from the electric (rear subframe mounted) fuel pump on the '65 998 Cooper, particularly when it's running on fast idle.

Should I be worried and be trying to source a replacement soonish?

Cheers, Ed.

[mk1]

They always make a bit of a knock, knock, knock as they are pumping. It will increase in rate as you use more fuel.

[Peter Laidler]

Agree with Mk1 - above - but am concerned at what you describe as a '.....knock'. There is a distinct 'tap tap tap tapping that is SU's way of letting you know that all is well on start-up (that'll stop once the fuel line and bowls are primed). But not a knock...........

Tell us more about the 'knock'

[IslandBlue]

I've always thought of the pump noise as being a "knocking " being lower pitched than what I'd describe as "tapping." All rather subjective.

Quite reassuring to hear when turning on the ignition I always think!

[timmy201]

The SU pump sits inside a rubber isolator in the pump hanger. Is the rubber still in good condition?

[mk1]

I've always thought of the pump noise as being a "knocking " being lower pitched than what I'd describe as "tapping." All rather subjective.

Quite reassuring to hear when turning on the ignition I always think!

Ditto.

[tweedy998]

Hi all,

Very many thanks for all your kind responses. It sounds like it's fairly normal. There has always been the little series of 'clunks' on switching the ignition on, which I've always taken as normal fuel pump priming.

The other 'knock' or 'tap' is mainly intermittently at a fast idle and only audible by standing next to the nearside rear wheel, I can't hear it in the car and have a feeling it disappears as the revs rise in any case. I'll put it down to a SU fuel pump foible for now given everyone's kind advice. Much appreciated as always.

All the best, Ed.

[IslandBlue]

I've always imagine that the initial knocking noises are as the pump runs to pressurise the system. Once that is done it only pumps as required so the noise is more spaced out. Presumably pumping constantly at high speed but you wouldn't hear it above all the other racket!

[Peter Laidler]

Further to the comments regarding the rubber wrapping around the pump, between it and the bracket. Many years ago I bought one of those thin close cell silicon impregnated foam floor mats used by gymn bunnies. Cheap as chips from Blacks. Cut a piece to suit and it's been trouble free ever since