Noise thru fuel lines in VS V6

[smaddock]

Ok, I know people are probably sick and tired of trying to diagnose other peoples noises by way of description, but here we go again.

My VS V6 has had cam, heads, valve springs, retainers, comp cams lifters all done, and over the last 3 or 4 months, its had a strange 'knocking' noise down low in the rev range. It started only being audible at idle, but as the months have gone by, its become more apparent up to around 2000rpm. You can't hear it all the time, it sorta pulses in and out, like it will knock for a few seconds, then stop for a few more, then come back, etc... It used to only do it while it was cold, but now it is doing it more and more while its warm.

I've probed all around the engine and tranny and can't hear a damn thing, however not long ago I got under the car while it was idling, and with a screwdriver against a fuel line as a stethoscope, there was the noise! Its as though something is causing the 'knocking' noise in the fuel line, which must be vibrating thru the body, hence why I can hear it inside the car, but not under the bonnet. Now it is a 'knocking' noise, not a 'ticking' noise, so its not injectors. And besides, I can't hear it in the fuel rail.

Would it possibly a buggered fuel pump? or maybe a fuel reg? Its really got me stumped, but thought since its getting worse, I may as well try to chase up what it could be so I can try to work out a fix for it...

Simo

 

[hako]

I'd doubt it has anything to do with the fuel line - this is just acting as a conduit to the noise. I think they're called "harmonic vibrations" and make themselves apparent when something or other vibrates in phase with something else which turns it into sound. (sounds like claptrap eh!). A bit like the way a record makes sound only more to do with rotational forces which eventually cancell themselves out when a certain rotational speed is reached. Your engine has got many many things going round, up and down and in and out and each or all will cause some vibration or other as most are not always in balance.
I think I'd be keeping an eye on things but probably it is nothing to worry about. Good Luck.

 

[smaddock]

Yeah the prob was that I've probed all round the engine and tranny with the 'screwdriver stethoscope' and cannot hear anything out of whack... not sure if harmonic balancer could cause this noise as that was another thought, but i figured I'd be able to hear that with the bonnet open. Oh well, gotta keep poking round I guess...