Occasionally, my Facet Silver Top pump produces a hard knocking noise.

Its only a couple of years old, and the knocking can last for several minutes. Only really noticeably when idling or slowish road speeds, but when it starts it is embarrassingly loud enough to make you want to turn the engine off when in traffic.

Has anyone any ideas what might be causing the problem? Are there any user servicable parts inside?

[Edited on 11/5/08 by lotustwincam]

You must be drawing in air somewhere, that's why it starts to hammer, as you start using fuel at a decent rate the air bubble moves on.

The best cure is a tank return with a restrictor to bleed off some fuel, favorite restrictor is an old idle jet poked into the return pipe held in place by a jubilee clip.

If you look at production cars with this type of pump they also had returns, range rovers spring to mind.

Regards Mark

Thanks Mark,

What you say makes perfect sense.

Since it has been working ok until recently, I'll investigate the possibility of an air leak in the fuel line first.

As the pump is located in the engine bay, I reckon it would have to be a connection close to the pump end which would be slightly above normal fuel level.