gt40 1998 stalls above idle speed in gear

[nuffejohan]

Thanks for sharing your knowledge with me. I have a Ski Nautique 196 from 1998 with the GT40 engine, and my problem is that when I apply throttle, the engine stalls above idle RPMs (in gear). This means I cannot really apply any kind of throttle because the engine sputters and drops way low in RPMs. However, in neutral, I am able to apply throttle up to 4500 RPMs if I do it gently. If I just slam down the throttle, it sputters and backfires.

Things I have done for the boat this season include replacing the high-pressure fuel pump. The engine starts very easily and idles well. I also replaced the fuel filter, both the one at the gas tank and the one at the FCC. The filter at the fuel tank was in bad shape, but now that it’s replaced, the problem still remains.

I am thinking about checking the valve in the gas tank and will try to remove it to ensure it’s not causing the issue. Is there anything specific that would make the engine die at anything above idle in gear? Thank you so much.

[Kmayotte]

Kind of funny you post this today as I was researching this today for my boat as I have a similar issue. On my and maybe yours, I suspect the Idle Air Control Valve. It can be taken out and cleaned.

I found this thread to be helpful. https://www.planetnautique.com/vb5/f...ZfUzPCCbfnLFbw

[Tom_H]

When was the last time plugs, wires, cap were changed? Maybe an issue with your TPS sensor, and the air/fuel ratio is going to crap as you throttle up. Fuel lines, if original, could be collapsing internally on you too, and yea, it's not a bad idea to pull your anti-siphon valve and make sure the ball is freely moving.

[FMSKI]

If you hookup a fuel pressure gauge on the rail and monitor, that it will rule out fuel issues. Very easy to do and inexpensive. So you just watch the gauge and if pressure tanks you have a supply problem.

Pressure is solid and in spec (40-45psi I think) then I would look to the distributor itself (ignition), if it is original and rusted up.

The idle air control valve will cause idle speed or control issues but it should still run and move at throttle.

[Kmayotte]

The idle air control valve will cause idle speed or control issues but it should still run and move at throttle.

This is my issue, no problems above idle.

[Jonny Quest]

For under $500 you can update your GT40 and improve performance and reliability: new 24 lb injectors, new fuel pressure regulator, new high/low fuel pumps, new FCC filter, new MAP, new TPS, new IAC, new cap, rotor and wires. I did this to my 2001 Ski with great success. Strong engine.

Note: the only PCM parts I used was the FCC filter and high pressure pump. The rest was FoMoCo and a few after-market.

JQ

[SilentSeven]

+1 for it likely being the idle control valve.