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'97 GT-40 miss or sputter.


Wish
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Skid this evening. I skied first, boat ran great. I drove second set for a buddy and around the pregates the boat had like a pop sound, quick little surge after. Then again half way down the course and then tawards the end again. Made the PP surge a little. Skier got in and we just ran it down the lake no PP. It did a very intermittent miss (pop) after getting up on plane. Did not go 34mph..more like 25. Did it about 3 times length-ish of the course. Idles fine and having it in gear seems to be ok as well. Did put in 9 gallons before sets and a can of SeaFoam fuel additive (I do that a few times a year). Bad gas?? Check fuel cell (water/fuel separator)?? Drain cell?? Change it?? What else could it be?. Plugs and Wires and dis are not that old. Onset was certainly sudden.
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  • Baller

@Wish Depending on how far off it is it can give you everything from an occasional sputter to a no start situation.

Point is, it is not monitored by the ECM and will not light up the fault lamp or generate fault codes. If you have access to a fuel pressure gauge you can rule out the entire fuel system minus the injectors with one quick measurement.

 

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I’d bet money on fuel cell. I’m not sure what fuel pressure should be but I’m guessing no less than 48psi throughout all rpm’s. ECM’s typically won’t tolerate much of a drop, maybe 6psi. If you don’t have a gauge the one from Harbor Freight will work and plug it into shraeder valve on fuel rails. A flat idle or even sometimes a long smooth acceleration won’t cause much of a drop in pressure. That motor should only require 2-3 plugs sets in its entire life. Today’s wires aren’t like the ones from the 60’s. Unless one was burned or gnawed on, the original set should last life of the engine. I’ve had dizzy’s in the past that didn’t like being in a boat, closed up in the motor box without being opened up and aired out every trip. But those seemed to be just points style.
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Make sure it's really a misfire and not the S.L.O.W system kicking in intermittently from a bad oil pressure sender or temp sender. This system abruptly cuts power to protect the motor in a low oil pressure or high temp situation and it's quite unsettling when it kicks in. The check engine light would light at the same time if this was the case. If it's truly undoubtedly a misfire then ignore this.
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A bad tac can make it miss ,i used to be able to tap on the face of tac make it skip fix new tac ,another time i had a worn spot in my main harness the big red power to dash it was under the floor and 8 hours trouble shooting to find it anyway both made it skip mostly from boat hitting bumps small ripples jiggling boat
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This is almost certainly a fuel or spark problem (I know that seems obvious, but bear with me). I don't recall Nautique fuel pressure off the top of my head, but it's less than the MC MPI systems. The guys at Discount inboard marine will surely offer this up for you. If pressure is good, it could easily be wet fuel. Sea foam will look after a little water, but more than a little will require methyl hydrate, and time to burn through the bad fuel. Decanting a few ounces of fuel off the fuel rail and allowing it to rest in a clear container will likely declare wet fuel (it sinks to the bottom, of course). Regardless, replace the filter in the fuel cell if it hasn't been recently done. The next thing to check is spark with a timing light, on each plug wire sequentially. I worked on a GT40 with a miss 2 years ago. Proved to be a bad distributor bearing, causing intermittent lack of contact between cap and rotor only at two cylinders. This condition was diagnosed with a timing light. And no, check engine will not be triggered with this issue. That said, the poster indicated the distributor is pretty fresh.

 

I'd be guessing the issue is fuel, either bad filter or pump causing marginal pressure, or water in fuel. But the proper diagnosis starts with establishing fuel pressure and proper spark at all cylinders.

 

How many engine hours, and is the check engine light on?

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No light and 1300hrs. As said, had just added 9 gallons to a frailly empty tank and added SeaFoam to that. It did run flawlessly the first set. Second set it started missing immediately on getting up to speed but only 3 times down the course and only a single split second miss. My gut says bad fuel or water in system. I've ordered the filter. Will drain cell tomorrow and check for water. Open to other thoughts and ideas.
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This could be a dumb answer, but I would check you water intake to make sure it isn't plugged and overheating. Our boat gets clogged often and will sputter and loose power before the red overheating light comes on. Most likely you a fueling issue, but it only takes a second to check!
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Sometimes a cap can get a small crack in it and will be affected by moisture. I had a truck that had difficulty starting/running after a rain. Changed cap and rotor and all was well. This was after I had the truck for 20+ years, probably about the same age as @Wish boat.

The worst slalom equipment I own is between my ears.

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So boat is running fine at idle now with new fuel filter, distubuter and rotor. Did not take it for a run as we noticed the tiniest of a pin hole leak where the wires comes out of the top of the FCC (see pic). Looks like there is a sealent product applied where the wire for the hp fuel pump exits the FCC. Anyone know what product that would be?. It's some sort of compound for sure as it is pliable. Obviously it's not affected by heat or fuel.

 

4boa0v3rcc83.jpeg

 

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So this is where I am at:

 

1997 GT40 1300 hours

 

Initial symptoms and chain of events:

 

Normal ski day and pretty routine. Went out and took a 6 pass slalom set. Boat ran great at 34mph. Back to the dock were motor was turned off. Took a second set 15mn later. Skier was picked up, we entered course and the boat had what felt like a single miss. Could hear the faint pop and could feel the split second deceleration. Even the Perfect Pass compensated by apply a hint of throttle. Half-ish way down the course it happened again and one more time before exiting the course. We stopped and turned motor off. Then proceeded to run boat outside of course with PP off and at 25mph-ish. The boat made 3-4 single misses at that speed roughly the length of the course. It idle fine as well as just in gear. Right before the 2 sets that day, 9 gallons of gas was added along with one can of Seafoam (Seafoam put in tank a couple times a year)

 

Next day...What has been done since:

 

-New fuel filter and new pass through wire harness for the FCC.

-New rotor and cap

-oil pressure switch (next to FCC) volts tested. Results; 5.7v @ 2000rpms, 6.3v @ 720rpm and 7.2v with ¼ turn of ignition key/motor not running. Not sure if that means anything

 

Symptoms persists:

 

Test ran it at idle speed and it sounded fine. Idled around lake for 10mn. Stopped, then took off and ran it up to 25mph for a little more then the length of the course. It ran fine. Stopped, turned around and took off up to 34mph same distance. It ran fine again. Turned off motor. Turned on motor and idled again around lake for another 5-10mn and set up for an actual course run. Took off and it missed as it came up to plane, and before entering the course close to 34mph it missed again. Went back to in gear idle speed. Attempted a couple more runs up to 25mph but within 100-200 feet it would miss so it was brought back to in gear idle speed each time where it ran well. Low pressure fuel pump primes as normal with key turn as evidenced by its sound.

 

Next day...Whats been done:

 

-Disconnected the oil pressure switch as it was easy to do and mentioned.

 

Symptoms persists:

 

Wow, talk about consistency. Once again it ran soooooo gooood for what would have been like any first set. Ran it through its passes with no issues at all for 10+ minutes. Back to the dock, let it sit for 15mn engine off. Idled out to course and it idled fine. Took off to get up on plane, and about every 100-200 feet same thing..single little pop and a split second drop in performance and right back to normal for another 100+ feet..then pop.

 

Seems to me that if it was bad fuel it would not run great initially like it has all 3 outings. Also to me it rules out fuel pumps...maybe. Also to me rules out low fuel pressure of any kind.

 

Totally lost as to where to go from here. But is is consistent.

 

 

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seems that way. While out initially it runs fine and is most certainly up to temp for as long as I run it. Can even idle around for a while and the temp goes up some (less freshwater circulation) it still runs fine. Let it sit for 15mn (motor box up) and it has problems if run again. Maybe temp rises while sitting without water circulation causing something???? E-Coil Pack???
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Until you check your fuel pressure you won’t be able to solve this. It sounds distinctly like a failing low pressure fuel pump. Heat soak causes real

Issues like this. If you’re on your original low pressure pump it’s time to replace it but please verify with fuel pressure first.

 

There’s a poor man’s GT-40 troubleshooting guide on Correctcraftfan that is head and shoulders the best thread anywhere for troubleshooting these engines.

 

I had a fuel starvation issue when I bought my used 96 Super Sport and had to go through a similar roadmap. It was my low pressure pump that solved the problem. You will find a whole host of little things that can go bump in the night but you’ll solve this.

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I would do a quick compression test to rule out anything major. Hopefully you won't find an "Oh Shit". Your problem sounds really funky.

 

At the risk of being Captain Obvious:

When was the last oil change?

Is the oil clean on the dipstick?

Is there a history of oil consumption?

Any blue or white smoke, or unusual exhaust smell?

 

Did you call Vince at Skidim or Jody yet?

 

If it was easy, they would call it Wakeboarding

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