Problems running under load - 1997 Ski Nautique GT40

[RickB_2000]

My 1997 GT40 is running fine when not pulling a skier. I can run it up and down the lake at 40MPH with no one on the back however when I try to run the course it bogs down by the time I can to 1 ball and then either stalls or runs rough.

Last fall, replaced the Cap/Rotor and wires and it ran fine in the driveway after doing this. When I started it this spring, it ran for 5 seconds, it died and then couldn't start it until I replaced the fuel pump. The fuel pump was occasionally sticking at the end of last season.

I put stabilizer in the tank last fall and added some gas this year.

Next step is to check the plugs (4 years old) and drain the water separator.

I'll also add sea form and fill it up with all new gas.

 

Any suggestions to what may be the problem?

 

Thanks,

Rick

[Chef23]

Did you check the fuel filter or filters if there are multiple? We have fixed similar problems on Malibus with replacing fuel filters.

[Fam-man]

We had a similar problem in a MB Sports with GT-40. After a bit of messing around we found rag material plugging the fuel inlet at the tank.

[Roger]

When my GT-40 acted like that, it was the plugs...

[wskier]

40 mph is that full throttle my 1999 snob goes 46 full load no skier I get up to 47.5 with just me in the boat

[TEL]

Like Fan-man said, check the inlet pick up tube in the tank most boats have a small screen on them and get plugged with junk from the bottom of the tank. when ever I replace my fuel filters I always clean the inlet screen. I have seen some screens missing and they get plugged up with all kinds of stuff.

[Edmund]

I agree with both @Chef23 and @Roger. If you have not changed the FCC filter in the past year, try it, and changing spark plugs may help. The FCC filter may last a year or two (or five), but the recommendation is to change every year.

[Edmund]

Which fuel filter did you replace; the high pressure or low pressure?

[DanE]

If you have access to a pressure guage and a vacuum pump with vacuumeter, correct info and know how to check fuel pressure start with that. If fuel pressure is correct you can leave all the guesswork regarding clogged screens, lines, filters and pumps behind.

[yardsale]

another bugger on the gt40 is, the 1/2" OD x 3" long rubber hose that is connected to the small fuel pump inside the fuel separator/filter. sometimes that hose can crack and cause motor to stall/cut out, behave poorly, etc. as it cannot hold fuel pressure.

 

There is a retro kit sold for it on planet nautique, I believe. Pull the fuel separator apart and inspect the hose. Pretty easy to get at.

[yardsale]

easy to then also change the fuel filter once you have the separator unscrewed and found a spot for the gas it contained.

[pudgyskier]

+1 on the 3" hose inside the FCC. A lot of times it is cracked and very hard to tell visually if there is a problem. If you change plugs, check all the screens, change the fuel filter, change the 3" pump hose, AND still have a problem, check your muffler. We struggled for a year with low power under heavy load on our GT 40, no problem with 1-2 people in boat and 120 lb or less skier, but 3 people and/ or 190 lb skier, we had about 50 % power loss. After posting on a few sites, someone on BOS suggested checking the muffler to see if it had come apart. I cut it open with my dremel, the inside baffle had come loose and was blocking the exit hole. I re-fiberglassed it in place, and then fiberglassed the top part of the muffler back together. I cut the top off like a pumpkin, ( 45 degree angle ) so the lid sat back in place and was easy to glass back together. It runs like a dream with 1400 + hrs.

 

 

 

[DanE]

At the risk of sounding like a broken record check fuel pressure first when troubleshooting, it's either correct or it's not and it needs to be correct If the ECM is going to control the engine.

[RickB_2000]

Thanks for all the tips. The boat will do about 46MPH wide open.

1. I checked the tank intake - clean.

2. Replaced the plugs.

3. Put Sea Form in the engine to blow out the carbon.

4. I checked the fuse in the battery compartment.

5. Running in the driveway, there seems to be a slight hesitation when I rev the motor just past the neutral position and then its fine.

6. I'm having issues unscrewing the FCC. Whoever installed it before me really tightened it. Oil filter wrenches don't work so next step is a BIG pipe wrench.

7. Waiting for the Fuel filter to arrive. I'll replace the fuel filter and 3" tube inside the FCC.

[Drago]

Had one back in the day. Pulled at 34, but a big guy at 36 didn't work. Felt like girl prob, was one spark plug wire

[A_B]

I had some issues pulling skiers and it ultimately was a faulty ECM. There is no fault code to read on those. The PCM tech that I talked with basically said you go through everything else and if they are ok, it's the ECM.

 

The FCC filter is an easy change once you break the FCC loose. But not sure how pulling a skier would be impacted by that if WOT is not. I did all of that, and pulled my gas tank to check for stuff, and replaced the backflush check valves.

 

Did you check for constant pressure on the fuel rail? That is where I found my problem.

The fuel pump would not maintain consistent pressure. I replaced the low pump and high pump in the FCC. Ultimately, the ECM was not running them consistently. Some BOS guys got some good deals on backup pumps from me.

 

The ECM's in these engines is a weak sister,

along with the fuel pump relays. Easy to carry backup relays. Almost like you need backup ECM while you can still find them.

[pudgyskier]

@RickB_2000 Well ? Any luck ??