1999 Ski Nautique GT-40 High Idle (860ish RPM)

[SlapChop69]

Good afternoon, I've been lurking this forum for a while and now that I'm in possession of my new (new to me) 1999 ski nautique I'm working through all the elements of the TLC it so sorely missed and deserved.

One of them is the following 'issue' I'm having.

The boat starts up fine, but then proceeds to idle at around 860ish rpm. It also seems to have a bit of a rough idle, and feels like it misses every now and then, especially when first put into gear. It feels like the rpm is fluctuating a fair amount, but isn't directly reflected on the tach or my perfect pass display. It has yet to stall though. It smoothed out a bit after warming up, but was still rough and idling at 860 after a good 40 minutes of driving.

This is contrasted by the fact that the hole shot and cruising is unaffected. It's strong out of the hole and runs like a top at every speed over about 1000 rpm. Certainly a day of skiing on Saturday saw it run flawlessly for what we needed.

The boat itself sat for about a year before I bought it, and looks to have been out in the elements, judging by the surface corrosion found on some of the metal hardwear in the interior, and found in places on the engine itself.

The battery did die on me on Saturday when I was installing the upgraded perfect pass system, though I had chalked that up to having had the accessory mode, auto bilge etc running for large periods of time without the engine running, so I've taken that out and put it on a battery charger (it was sitting at about 75% charged following a 30-40 minute continuous drive).

I've through some of the other GT-40 idling threads but haven't found a situation that clearly mirrors my own, so I figured I'd ask the crowd.

Thanks in advance!

[SilentSeven]

Any chance you have someone near you who can run a diacomm scan? If so, see if you can get that done.

Here's a few things to consider:

1. Look for an air intake leak - pull the spark arrester and look at all the various hoses.
2. Check the idle control valve.
3. Check the engine temp sensor; verify it's sending the 'engine is at operating temp' signal.
4. Check your alternator. Start with the cap and rotor. Also inspect the hall sensor. My '87 GT-40 had some odd problems that cleaned up with rebuild distributor. You can get a cardone re-manufactured one for small $ vs buying a PCM replacement. I have a thread somewhere with part numbers.

If I recall, in the manuals section on the board, there's a GT-40 manual and it has diag processes.

[SlapChop69]

Not sure about the scan, I'll ask the marina's near by - one is a mastercraft dealer (who also sells other ski/wake boats) so they should be able to have a look at codes with I'd assume.

I'll look at points 1 and 2 when I'm back at the cottage this weekend, in the mean time I'll look at getting the parts for the alternator. I wouldn't be surprised if the distributor needs replacing based on some of the incidental rust and corrosion that formed on the boat during it's year of non-use. It also has 1700 hours on the engine, and I'm not sure when the plugs, wires and distributor were replaced last.

[SilentSeven]

Found the distributor thread.

https://www.planetnautique.com/vb5/f...r+part+numbers

Post 11 has pictures of the guts of my distributor.

https://www.planetnautique.com/vb5/f...one-seen-this=

I'd still look for air leaks first.

My boat had ~1600 hours when I did the distributor replacement.

Post 3 in this thread may also be helpful

https://www.planetnautique.com/vb5/f...le=#post345989

[SlapChop69]

You are a gentleman and a scholar. I'll order the distributor parts as I may as well replace it sooner than later, I think it's the original and I'll check for leaks along with the air controller while I'm at it.

[SilentSeven]

Keep us updated. Stories with an ending are appreciated. Good luck!

[SlapChop69]

I shall, I ordered a distributor cap, rotar, wires and plugs. I figure I might as well give it a tune up as the wires look original, and I'm unsure if the rotor has been done recently - the spark plugs also look a little old.

I should have an update Saturday evening!

[SlapChop69]

One last question regarding spark plug wires - do both ends need to be 90 degree boots or would the 45 degree boots work?

[SlapChop69]

So an update from this morning: after having replaced the distributor cap and rotor, it is running noticeably smoother. The battery has also been fully charged.

there is an interesting discrepancy I hadn’t noticed before - perfect pass shows the rpm at idle still around 800-860, but the tachometer is showing a clear 680 and definitely 600 when idling forward. Are there any known accuracy issues with the perfect pass recording?

finally, I’ve attached a picture of the rotor and cap below, the corrosion was fairly bad. This afternoon I’ll place the spark plugs which should help as well. I imagine they haven’t been changed in a while based on what I’m seeing. Turns out the plug wires may also be original, so that’s on the list now as well.

[SilentSeven]

Nice progress. New wires should help m- they did on mine. Sorry I don't know the 45 vs 90 degree answer. How did the guts of your distributor look when you had the cap off? I think the hall sensor starts to get flakey after a lot of hours leading to odd ignition hiccups and other behaviors.

Check PP documentation on RPM lead setup. IIR, there is a choice to set the RPM lead a positive or negative ground or something like that. It's possible the setting may not be the optimum one leading to the variation.

Finally, on my '97 Ski the dash wiring is harness is completely under designed for both power and ground. I had issues with my PP cutting out that were only fixed when I ran a dedicated separate power and ground feed to the dash. Powered the PP and the stereo head unit. Not saying this is your problem but if you still having issues, consider running a secondary ground wire from the dash harness side direct to the battery to create a better ground. Poor grounding could also be part of the problem. I posted a thread on my dash relay project; I'll see if I can find it.

[SilentSeven]

Here's my dash wiring upgrade. Was a decent amount of work but slayed all the dash power and ground problems.

https://www.planetnautique.com/vb5/f...fix-with-photo

[SlapChop69]

A little update - I'm still waiting on the plug wires from the Nautique store. Some fairly egregious Fedex delays (over a month and a half) have meant that I've been waiting on them and a couple other items like a new throttle and shifter cable far longer than anticipated.

Otherwise, while it has been running well it is still exhibiting the surging at almost exactly 34 mph every time and loss of top end. A newer development yesterday was hard starting, eventually starting then cutting out right away, then after giving it a moment it started and then proceeded to run fine for over an hour. It started up instantly after I had shut it down from the hour of water fun.

I will be replacing the fuel filter today and doing a fuel pressure test now that I have a tester so that I can eliminate any fuel delivery problems - it could have been some water in my gas that caused the starting issues though, I did put a jerry in it on Saturday that had been sitting somewhat unprotected in the massive rain storm we just got, and the rear breathing port of the jerry was a bit damaged and probably let some water in.

In either case, I will also look at switching the leads on the PP, as it still typically reads a couple hundred RPM different than the TACH at pretty much any engine speed. If I go by the TACH, my idle is fine, and judging by the sound of the engine. This week will be more about boat maintenance then use after a couple of busy weekends, so hopefully I'll corner this little issue and it will be running perfectly in a week.