GT40 Problem

I have a 97 Supra Sunsport with a GT40. Yesterday I took the boat out and while we were all wakeboarding I noticed that the boat was a little sluggish getting out of the hole but it would still get up to riding speed with the ballast full. After 3 of us wakeboarded we decided to surf and added a little extra weight (probably not more than 1500lbs total ballast plus 3 people) but it would not go higher than 8.5 mph. I thought maybe it just wouldnt plane because of how the weight was setup but then we drained all of the ballast and it still would go faster than 10 mph. After that we idled back to the dock and on the way I started noticing that it was backfiring. It did die a few times but it would always restart and we got back to the dock ok. Engine is a fuel injected GT40. Does anybody have any ideas? It seems like I remember someone on here having a similar issue not too long ago but I couldnt find that thread. Thanks.

check all the spark plugs, make sure everything is snug.... that would be my only advice

I had that issue last summer (i think I posted on it). My motor is carburated though and that was the issue. It was only firing on like 5 of 8 or something crazy like that. Sounds like all yours arent firing, but I am definately not an expert. Like Nick said, spark plugs would be my first thing to check, since its the easiest, hopefully they are just fowled up and you have an easy fix!

your engine is going into "limp mode" and this is can be caused by a variety of reasons.
The first things to check would be
1. Impeller/ strainer to make sure it is clear
2. fuel filter is clear and new
3. spark plug wires are good and on securely
4. oil is at proper level

Limp Mode protects your engine to avoid damage. Did you happen to check your gauges and see if they were at the correct temp., oil pressure, etc...

Limp Mode can also be triggered if there is a made sensor in the engine. A little more information on the exact circumstances would help with the diagnosis.

Thanks for the replies. Out of your suggestions I can for sure rule out the impeller and oil level both. Both of those seem to be fine. The spark plugs looked ok too but I am going to go ahead and replace those just to be sure.

As far as the filter goes does anyone know where it is located on a 97 Sunsport. I have 2 fuel lines running from the tank? One to the low pressure fuel pump and one to the high pressure but I dont see any inline fuel filters on either line. The lines come out of the top of the tank towards the back of the boat and then snake down around and under the tank back towards the engine. The only place there could be a filter that I cant see is in that area between the tank and the back of the boat and I would hope they wouldnt have put it there just because the only way to get to would be to pull the entire gas tank.

As far as other symptoms go it seems like I have to crank on it a little more than normal to get it to start and after I start it for the first time it will die immediately. I can usually start it right after that though and it will stay running. The only other thing is that if I try to rev it a little it will sometimes kind of stutter and backfire.

(Message edited by maxx_wake on May 10, 2009)

I had my oil pressure sending unit go out on my 99 GT-40 and it caused the engine to go into limp mode.

From what you have listed I would say you have a fuel delivery problem. The high pressure fuel pump inside the the Filter/Water separator canister is known to have the rubber fuel line fail. I would check that too. Skidim sells a replacement line for it.

Check spark, fuel delivery and then start looking at sensors.

Limp mode will usually run fine up to about 2400 rpm and that's as high as it will rev. Below that the boat will run normal so it doesn't sound like that is your issue.

Chris let me explain how your fuel system works on your boat so you may understand a little better how it works and what your problem could be.

Correct Craft has a very nice system on the GT40 and their other motors which consists of a fuel pick up coming out of the tank and going to the LOW PRESSURE fuel pump located on your engine. The low pressure they provides a constant flow of gas into the the "FUEL CONTROL CELL" which is the canister right next to it. The LOW PRESSURE pump fills up this canister and then has an overflow or "return" line that goes back to the gas tank. This is why you see 2 lines coming from the tank. Correct Craft designed this system so that the HIGH PRESSURE fuel pump located inside the fuel control cell would always have constant fuel to pull from. In the event the boat went into a turn and gas sloshed to one side of the tank where the pick-up couldn't get to it....the fuel control cell provides up to 4 minutes of run time all by itself!!

So now the fuel control cell is where the fuel filter is actually contained. You should really change this every year but most people don't and some have never done it at all. changing that could help your problem.

Within the fuel control cell is, like i stated, the HIGH PRESSURE FUEL pump which has a rubber hose to send fuel outside of the control cell and to the high pressure fuel rail. This is where your problem may en lie. The hose may have broken down over time and gotten a small slit it in so the engine is not receiving its full capacity of fuel.

You have to take off the fuel control cell and unscrew the bottom off the canister in order to see the inner workings. It will take bench vise and a few strap wrenches because they are usually screwed on very tight from the factory. Also, don't do this unless you have a o-ring kit and new filter to replace the one it there. Remember to apply some grease to the threads when you screw the canister back together.

Sorry for the long explanation but everyone should know how their own boat works!!!!

Bill,

Thanks for that detailed explanation. I consider myself to be somewhat mechanically inclined but it is so much easier when someone can tell you exactly how it works instead of trying to just figure it out on your own.

The only other time I have ever had a problem with this boat was when I took it for a test drive before I bought it about a year ago. It stranded me and the previous owner. Needless to say he had to fix it before I bought it but it was the high pressure fuel pump that was the problem and I am pretty sure the dealership replaced it. Since then it has run really strong up until Saturday. Anyways, I went ahead and ordered a new filter along with some new spark plugs and wires so I will replace those as soon as they get there and hopefully it will be that easy of a fix.

Glad to help, let us know if that fixes it.

it's funny how you figured out your engine was not running properly that day and you continued abusing it.

whoa whoa...he is obviously not abusing it because it's not like he loads it up with 3000 lbs. and then tries to hit the throttle. Chris can obviously realize that the boat is not running right and he is doing his best to diagnose the problem on the lake and we're (people on the forum) are trying to help him. It's a hard problem to figure out and if it were to happen to you, you too would soon realize that a test run of the boat every now and then to see if the problem is still there would help to diagnose the malfunction.

If your car/truck starts running bad do you park it in the driveway and forget about it...maybe hope it fixes itself. NO, you have to drive it in order to figure out the problem.

And FYI, the GT40 is bulletproof. You can abuse the @#$% out of it and the engine will just keep on going.

Bill I agree with you and it was not my intention to offend anyone, but one thing is to test drive it and another VERY different is to go wakesurfing.

Then I'll add another suggestion, crappy fuel.
We had a boat with a GT40 and it didnt like certain places fuel.

"when I took it for a test drive before I bought it about a year ago"
the year ago test drive? that resulted in a new HP pump?

Anywho, great explanation Bill.

Yeah, I guess I wasnt completely clear with my first post. I didnt realize there was actually a problem until after we surfed. I did notice that it seemed a little more slugish than usual which kind of bothered me but I decided that it was just because we were running a little more weight than usual. It wasnt until after we were done surfing and drained all of the ballast that I realized I definitely had a problem. At that point I tried every thing I could think of on the water with no luck so I ended up idling it back to the dock just so I could get it on the trailer.

Anyways, the new plugs, wires and fuel filter should be here today so I will let you guys know if that helps.

As far as the test drive a year ago that was a completely different problem. I just brought it up just to say the fuel pump was replaced about a year ago. We have had the boat out many times since then with no problems.

no worries Luciano but i would agree that bad fuel could entirely be a possibility. I would recommend running the boat off an isolated 5 gallon tank of fuel. You can do this by getting a short length of hose to go from the 5 gallon fuel tank to the low pressure pump. If you want you could also get another hose for the return line into the 5 gallon tank but it's not necessary.

I would actually highly recommend you isolate the bad fuel by running it on an auxiliary tank to check if the problem is eliminated.

Although fuel is a good thing to check and replacing the filter is definitely wise, the main thing that causes the engine to go into LIMP MODE is switches. The oil pressure and temperature switch can be faulty and trigger the electronics to prevent the engine from potential damage.

The switches simply complete a circuit and then send a signal to engine that something isn't right. You can defeat this system by pulling the leads off each sensor and then run the boat to see if it's a faulty switch. The temperature switch is on top of the engine and the oil switch is on the bottom of the engine near the front(i believe) A 5/16 socket should get the nut lose in order to take the wire off to bypass the safety.

Well I replaced the fuel filter last night and it seems to have helped. I ran it in the drive way with the fake a lake and it seemed to run smoother and no more backfiring. It looked like the old filter might have expanded a bit. It was wedged in the canister and I had to tap it out from the bottom through the drain plug. Is this normal? I am hoping to lake test it today or tomorrow.

(Message edited by maxx_wake on May 15, 2009)

I got out on the water for a short test run today and the boat ran much better than last weekend. I couldnt tell if I was being paranoid though or if it still seemed a little slugish. It would get out of the hole and on plane ok but it seemed like it might not have the same punch it used to so I am just worried that the problem could come back. I could just be imagining it though too. lol.

fuel filters are hard to get out no worries, i almost didn't think i was going to get mine out. Keep running it and run fresh fuel through the engine but if it's still sluggish we have to look at some other stuff.

BTW, I know I shouldn't have done this but I lit the old fuel filter on fire in the driveway and it was pretty cool. No explosion, just burned for like 10 minutes.

If the issue was fuel related, you might as well have dirt on your tank and very possibly some dirty injectors as well.

I'd also check your cap and rotor. I had very similar symptoms on my boat and didn't really notice it until we loaded it down. Anyway, it was beginning to misfire and was having a hard time starting. Putt putted back to the dock and checked the cap and rotor after towing it home. The rotor was corroded bad as was the cap. Replaced both and now it runs like a champ. Good luck.

Latest update. Took the the boat out again and it seemed like the symptoms were coming back. Everytime I started it would have a little bit harder time getting on plane. I think if we had stayed out much longer it would have gotten back to the point where it wont plane. I was thinking it was something to do with the gas so when I got home I drained all of the gas out of the tank and then filled it back up with fresh gas plus a bottle of fuel cleaner. It is very hard to tell from running it in the driveway if it has helped but I dont think it did. The latest thing it is doing is when I push the throttle just barely past idle the RPM starts to jump up and down. It starts to cyle between 1200 and 2000 RPM until I either give it some more gas or pull it back to idle. Even then it will continue to cycle for another 30 seconds or so before it evens back out at about an 800 RPM idle.