Unusual buzzing sound, GT40 engine

[ally505]

My GT40 occasionally creates an unusual loud buzzing sound that I am struggling to track down. The noise is coming from near to the throttle body, when I put my hand over the flame arrestor the pitch changes slightly. There is no appreciable loss in performance, revs stay constant etc when the buzzing occurs, so for now it is just one of these strange things. Turning the engine off and back on clears the noise, and it may be 5 minutes or 5 hours before it comes back again. I have recently changed the idle control valve (but unlikely this is related as the sound was present prior to changing it).
I am wondering if it is a sign that an injector is on its way out, maybe fuel pump? Open to thoughts on possible cause. Thanks!

[ally505]

here's a link to a video, first 20 seconds or so with the buzzing noise, then without after the engine had been restarted.

http://www.youtube.com/watch?v=tNsst...ature=youtu.be

[DanielC]

I do not know.
If you take a two or three foot piece of hose, hold one end up to your ear, and the other end close to the suspected source of the noise, you can narrow down where the noise is coming from.

[ally505]

thanks Daniel. I've got the same post running on correctcraftfan to tap into their wisdom also. it's definitely something electro-mechanical, that I do know! Frequency doesn't change with engine revs so it's not a harmonic vibration. Whats getting me is that the noise seems to be emanating from the throttle body, maybe it's just acting like an amplifier...... In my view (and with little experience I may add) it seems too loud for an injector and there is no poor running, coked or lean plug, so I think the only other thing it could be is the HP pump getting ready to give up the ghost.

[ally505]

just to be sure, the FCC houses the low pressure fuel pump and the high pressure fuel pump is up on top of the engine by the injector rail. Right? Does anybody have the p/n for the HP pump and is there a non marine alternative that meets the same spec?

[AirTool]

It's probably the bearing in the HP pump. Maybe you could jumper some power with the engine off and confirm.

The HP pump is in the canister. Here are the pumps:

http://www.nautiqueparts.com/fuelpumps.aspx

[DanielC]

What year is your Gt-40 engine?
I have a 1997 Ski Nautique, and the high pressure pump is inside the FCC. High pressure fuel comes out of the FCC, and goes to the fuel rails. There is a regulator at the end of the fuel rail, that dumps fuel back into the low pressure side of the FCC.

This is how you check fuel pressure on a GT-40 engine.
http://www.planetnautique.com/vb3/sh...=fuel+pressure

You may not actually need to check the fuel pressure, but you can use the information in the thread to run the fuel pumps without having to run the engine. Handy if the boat is on a trailer, instead of floating.

[ally505]

excellent, thanks, It's a 97 also. I will have a go running the pump to see if I can recreate the noise.

I am guessing if I confirm the fault, this is the replacement item I need

http://www.nautiqueparts.com/fuelpum...ntrolcell.aspx