GT 40- no full power

[DanielC]

For those of you trying to help, a GT-40 is a multiport fuel injection setup. The ignition timing is controlled by the engines computer, there is no adjustment on it.

You mentioned you ran the boat on Lake Tahoe. Is that not around 6,000 to 7,000 feet? If your boat runs 4800 to 5200 RPM, at or near sea level, (Sacramento delta) I would not expect it to run the same RPM on Lake Tahoe, without changing the propeller to a lower pitch.

[JayG80]

May be a crack in the short fuel line that the high pressure pump hangs on inside the FCC.

I like hole in muffler theory. Is your bilge dry?

[minasianj]

The bilge generally stays dry. I remember operating it at WOT with the engine compartment partially open and the problem persisted so I suspect the muffler is not the issue. I can't say what the performance is at sea level as we have only used it on Lake Tahoe (6000ft) but I am certain WOT has has historically yielded 4600-4800 RPM. The fuel line inside the FCC is not the original and seemed to be in good condition when we replaced the filter last summer but it may be worth another look. Is it possible that despite having normal fuel pressure a small puncture or leak in the fuel system would explain top end power loss?
Once again thank you all for your feedback

[DanielC]

You already have a fuel leak in the fuel rail supplying fuel to the injectors. It is called the fuel pressure regulator. The high pressure pump supplies more fuel than the engine should ever need, and the regulator bleeds off the excess to keep the fuel pressure constant. As long as the fuel pressure is within specs, WHEN THE PROBLEM IS OCCURRING, I think you can rule out fuel pressure as the root cause of the poor performance.

Have you checked the spark plugs for color on the ceramic insulator tip? If you have an injector that is malfunctioning, that might give you a hint of a cylinder not getting a full shot of fuel.

You may also need to find a mechanic who can put a diagnostic computer on the engine, while it is running, under load, in the water, and verify that the ignition timing is being advanced by the engine's computer. I believe the Ford electronic ignition ignition has a preset 10 degrees advanced setting, and when the ignition system receives the correct information from the engine computer, it will then advance the ignition timing farther than the 10 degree preset. You may also be able to check the ignition timing with a timing light, and see if the ignition timing advances as the engine comes off idle.