1998 GT-40 cutting in/out at higer rpm's, help please!

[177]

I have the GT-40 motor in my '98 sport nautique. When the engine gets to 2500 rpm and above it starts to cut in and out like it is not getting enough fuel. The check engine light is constantly on. The engine never completely shuts of but will rev up and down at any rpm above 2500. Below 2500 the engine runs normal. I also have to put it in neutral and give it a little gas to crank, which i did not have to before. The engine will not run at idle, only when a little throttle is applied (approx 900-1100 rpm).

I replaced the fuel filter thinking that was the problem. Needless to say it did not remedy my problem. Spark plugs and injectors are also good. My fuel pressure stays steady at 35-40 psi and does not change when the engine starts to go in and out. This problem began all of the sudden after about 3 hours of run time one day.

Any and all help or suggestions are much appreciated. Thanks ahead of time for your help.

[DanielC]

RE: 1998 GT-40 cutting in/out at higer rpm

If the check engine light is on, there should be some engine diagnostic codes that can be pulled.
Off the top of my head, I would suspect ignition system problems, focusing on spark plugs, plug wires, and the distributer cap and rotor.
You could get the boat hooked up to an ignition scope, and that will tell you the condition of the secondary ignition system, but the labor fee to do that is in most cases more than new plugs, wires, and a cap and rotor.
How many hours on the boat?
The fuel pressure should drop when the engine has high vacuum, from 39 psi, to around 31 psi.

[177]

450 hours on boat. Fuel pressure rises from 35psi to 40psi as revs build from 2500 to 4500 rpm.

[knowscc]

Start and run the boat while someone observes an accurate fuel pressure gauge attached to the schrader valve on the FCC. Pressure should NOT fall below 38psi at WOT. If it does, isolate the fuel tank (temporary auxillary fuel tank) and run the boat and see if your issue goes away.

[177]

turns out it was not a fuel issue at all. the cutting in/out was just the computer putting the engine into "safe" mode. The problem was a faulty oil pressure sensor. (the one that goes to the computer). replaced it, everything running perfect now! thanks for your help and suggestions.