1997 gt40 issue?

Hello everyone. Not sure where to start after such a poor day - blown tire, lost wallet, and boat started acting up (not in that order)

This is our first summer with our 1997 sport nautique. It has 333 hours on it. I was pulling my son today when the boat started to sputter. We went from seemingly limitless power to none! RPMs wouldn't go above 2500 when in gear. In neutral, the boat would rev fine, well into 5000 rpms. This continued for about 30 minutes, as I limped us back to dock. When I was about to enter no wake zone near dock, it cleared! So I decided to run the boat to test if it would come back. For one hour, it ran fine. No hesitation, no issues everything was normal. We were cruising at about 3500 rpm when it just started to sputter again. Same as before, could never go above 2500 rpm when in gear. It was a rough running 2500 rpms too, not smooth running. The boat never died, and started up each time I turned off.

Any guess to what we experienced? I do note the bilge had more water when this first happened. Somehow the pump was flipped off. The second time, no water in bilge.

Much thanks for any clues to check

Best,
Charles

Hey, thanks for responding. There were no warning lights on the dash. All gauges looked good too, temp, oil pressure.

Correct me if i'm wrong, but I thought limp mode would have the boat run well, but not allow RPMs to get up above 2700. My boat was running rough and wouldn't spool above 2500 RPMs in gear, but in neutral it would run great, and spool up to 5000 RPM no problem.

Thanks for clarifying!

Charles

Could possibly be fuel pressure related. I'd get a gauge and check pressure when the engine starts to sputter. If your pressure is dropping, it could be the low or high pressure pump failing so it is not pumping enough fuel to the rails under load (reving in neutral there isn't a load). Again, if it seems okay at lower RPM but starves at higher RPM under load, it could be a plugged fuel filter, or the screen mesh in the top of the tank pick up. Or it could be a pin hole (like I had) in the hose in the output side of the high pressure pump). Since it was fine for a while, it could also be relays, etc.

Anyway, the first thing I'd do is get a pressure gauge on the fuel rail and see what it is doing.

Got to your neighborhood tool rental place and rent a very large pipe wrench (cost me about $10). Leaves a few "marks" but not noticeable and I got it off easily that way. I should have done that from the beginning instead of going through all the broken wrenches and burst blood vessels. Since then, I've been able to get it off each time with just wrench-style oil wrenches.

First, thanks to everyone who responded. Getting the FCC was especially difficult. I found that previous owner used teflon tape to ensure a seal. Now I'm not a professional mechanic, but that same tape used to seal a shower head has no business in the fuel system in my opinion. It made the entire cylinder glued to the lid. I bought 24in pipe wrenchan pulled the fcc off and put it in a vise. I felt with the fcc mounted, I was torquing the mount too much. Finally got it off and used a steel brush to get all remnants of the tape off.

I replaced the fuel filter and went for a lake test. Boat still ran like crap! Wouldn't spool over 2500 rpms,and was rough. So I'm out in the lake, just wondering what the heck man! I start pulling plug wires from distributor cap, reconnecting to ensure a good fit. I do the same at the block. The 2nd cable I pull, the connector stays on the plug. I think hmm. I fire up the boat with the plug disconnected and it runs the same! Quick ride to auto parts store, nuw plug wire and the boat runs great.

Lesson here: your boat will run on 7 cylinders in neutral and sound ok. 7 cylinders in gear, it's going to struggle.

Best regards!
Charles

Yes, just a spark plug wire and problem solved.