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2004 GTX LTD SC RPM drops after planing - dealer is stumped and so am I!

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Cleaned all the fuel injectors. No change. Took the ski back to the place that did the supercharger. They checked the torque on it and said it was in spec.

Now what? Any more suggestions?
 
Changed to a different prop. Solas 12/20. Lost RPM. Went back to stock. Symptoms are still the same .

Also took off the entire exhaust system and checked for leaks and obstructions. None.

The gremlins continue. Any more suggestions? I haven't done a compression test in a while so that will be next.
 
What is the gap supposed to be? Usually I just take them out of the box and put them in the ski.

Sitting on the trailer or tied up in a slip, I can hit the rev limiter all day long. So why it gets weak when riding is still a head scratcher!
 
Plugs fail under load. The engine will run just fine on the trailer. Run it in the water, start to plane then blooahh. Supercharged SeaDoo's eat spark plugs.
For Aircraft spark plugs we have a pressurized tester. The tester blows in 140 psi then sends jolts to the plug. Bad plugs will spark until they are under pressure. Good one spark all the way to 140 psi. This is the only way to test plugs.

Spark plug gap is .030
 
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Pull the seat and take it for a spin. I know you said you checked for exhaust leaks but you never know. If it runs better with the seat off you have an exhaust issue.
 
So I'm heading out to mess with it again. On the agenda is to change (and gap) spark plugs. Run it with the seat off. And then pull the drain plugs and leave it if it doesn't run better.
 
Old plugs looked fine. New plugs ran same as old. Ski ran exactly the same with new plugs. And with no seat on.
 
In the jet pump assembly there is a 'plug' that controls how much water goes into the cooling/exhaust systems, you can see it from the top left side of the pump as a 24mm black plastic nut. If you open the IBR you can look inside the pump and see if the bottom portion of the nut is there or not as it looks like a 1'' disk with a bunch of tiny holes in it, I had one break off and the engine just would not run correct.
 
The marina saw me doing it and wouldn't let me sink it.

I checked that 1" disk when I had the pump off last. It looks like a screen. And it was present.

Is it possible that I just need a smaller prop? I mean yes I'm stock right now. I tried a solas 12/20 and it lost power. If I go with a shorter prop then I should get the power back, yes?

The stock was recently remanufactured, btw, so I know that is in spec.

And to reiterate, it runs perfect on the trailer and perfect when stationary in a slip (tied up). Bounces off the redline all day long. But when up on plane, it hits max RPM at the hole shot and then RPM settles back to 6900.
 
Question: so the stock impeller is 11/19. What if I drop to a 10/18... what will happen on this ski? RPM should go up. What about speed?
 
I was thinking maybe you could check the throttle body to see if it stays open, you can move it by turning the ignition on but not starting it up and then move the throttle. There are springs inside the throttle body and if one has failed or something else is wrong it will not stay open all the way, don't put you finger in there while doing this or anything else. You could remove the throttle body and still do the test. Stay with the stock impeller for now, because that is what it's tuned for. Has the dealer done a check for throttle position during the run? I am not sure if this is even possible but maybe a sensor is telling the ECU to throttle back, like the knock sensor or something like it, I assume you are using premium fuel.
 
So I have definitely checked the throttle body to make sure it is open all the way. I haven't checked it while underway. But the cable is pretty tight. I will pull the TB and check it though.
 
have you tried another prop of the same pitch? Sounds like maybe the 11 part is ok as you can hit redline but once the 19 portion of the prop is running it can't overcome the resistance like one of those blades is bent or something? Or even if you have a 10/18 hanging around and can hit redline on top end maybe it is a prop issue, redline on a 10/18 will be less mph than redline on a 11/19.
 
You said the SC was checked by the dealer and in spec but never said what the slippage torque value was. I wouldn't trust a dealer who is stumped by losing 700 RPM's. Have you checked your opas function?
 
What about the spark plug coil?
I remember someone had theirs fail. Or make sure you have dielectric grease around the quick disconnect and lubed into the spark plug head cavity. Could be grounding out to the engine.
 
Opas is fine. Took it off just to double check. Dialectic grease didn't do anything.

Strangely, a friend of mine at the lake just bought a used 2004 GTX. He didn't test ride it. It is literally doing exactly the same thing as mine. Let the gremelin hunt continue!
 
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