‘03 GTX 4-Tec Supercharged RPM Issue

[Nick10201]

I recently took my 03 GTX to the bahamas and on the way back it randomly made an awful screeching noise back aft and dropped in RPM and speed to zero from about 5000 rpm/ 30 mph. It immediately picked back up speed and RPM so I figured I sucked something up and it passed through. Fast forward five minutes and the same thing happened over and over and over until a knocking sound began within the ski and it wouldn’t go above 3000-3500 RPM without making the sound and completely stopping hard. I’ve been told it’s possibly the supercharger but the knocking is what worries me. It only knocks when it is in the water. When it is out on the trailer, I can hook it to a hose and run it all the way to 6000-7000 rpm without a single sound out of the ordinary or drop in rpm whatsoever. Something to do with the pressure of being in the water? When I’m in the water and do rev it whatsoever the knock increases in frequency like it’s something spinning and hitting something. Any advice?

 

[Greg Moore]

Check your impeller bearings, you may have blown them. S/C doesn't produce knocking sounds. Blown piston or dropped valve will but will knock on the hose too.

Look into pump inlet from underneath with a good flashlight. If you lost a pump bearing the impeller will have been banging around inside the wear ring and it will be pretty tough looking. Should be an even 30 thousands or less gap evenly all around. You can also try to move the drive shaft near the pump end if your hands are small enough to squeeze through the intake grate and see if any movement at all. Essentially shouldn't move period.

 

[mkov608]

Wear ring to impeller clearance is different between models; on 4-tec skis, the max gap is .014", ref 13-02-25.