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97 Sport Nautique Cuts out after warms up |
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BobinIL 
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 Topic: 97 Sport Nautique Cuts out after warms upPosted: July-04-2022 at 4:57pm |
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I have been dealing with this issue for 3 years now with no resolution. Below is my post from last year.
I have a 1997 Sport Nautique with a PCM GT40 engine. It has started to act up after about 30 minutes of use. When at speed or under load it will start cutting out like it is going to stall. As soon as you go back to idle it runs fine. It only does it after it warms up. I also heard a squeal when starting it up last night much like a loose belt squeal but my belts are new and tight.
In the last 3 years I have replaced - The fuel pressure regulator - All 8 Injectors - The High Pressure fuel pump (twice) - Fuel Filter inside fuel cell - Fuel control cell electrical connector because mine started leaking - The low pressure fuel pump - I have checked the fuel pickup screen inside the fuel tank for debris - I have drained the gas and replaced it with fresh gas - I have ran it until it starts cutting out with a pressure regulator attached to the fuel rail and it does show a loss of pressure at the fuel rail - I still cannot figure out what would be causing it to lose pressure only after warmed up and only at higher RPM |
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gun-driver
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Joined: July-18-2008 Location: Pittsburgh, Pa Status: Offline Points: 4112 |
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Posted: July-04-2022 at 7:50pm |
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Sounds like it could be the ECA diode like this guy had problems with.
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BobinIL
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Posted: July-18-2022 at 12:43pm |
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I called the Service Manager at N3 Boatworks in Indy. He immediately said your fuel pump resistor is bad. He said if you feel the resister after it starts cutting out it should be very hot. I have ordered 2 resisters and will update after installation. Fingers crossed this it the problem.
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KENO
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Posted: July-18-2022 at 12:57pm |
Hate to ask silly questions but what's a fuel pump resistor, where's it located and what's the part number of what you ordered?
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BobinIL
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Posted: July-18-2022 at 2:17pm |
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I apologize its the fuel pump relay. I have been doing a little too much wiring work on vehicles lately. Completely rewiring a 1981 IH 5088 farm tractor.
https://www.nautiqueparts.com/product/relay-pcm-for-gt40-fuel-pump-and-ecm-r130011/ |
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KENO
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Posted: July-18-2022 at 2:59pm |
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Thought that might be the case
 I think you probably already know to change the fuel pump and ECM relays at the same time, but figured I'd mention it.. You need both of the relays to make the fuel pumps run.
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BobinIL
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Posted: July-18-2022 at 3:07pm |
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Yes I ordered 2 relays from N3 Boatworks a week ago but they are not the same as the originals. They plug in ok but the rubber seal does not seal up. I happened to have one older relay on hand I think I purchased from Nautique parts a couple years ago that fit correctly. I just ordered a second one yesterday from NP.
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gun-driver
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Posted: July-18-2022 at 3:58pm |
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The diodes are 1N4001.
Here’s the original post for those that may not be able to follow the link above I have been on this forum multiple times over the past 3 years and haven't heard of anyone reporting this particular problem, but I'll bet others have suffered from it. I have a 1997 Ski Nautique with a GT40. Beginning about 3-4 years ago, the engine would, on rare occasions, shudder, partially quit, run again, sometimes quit altogether. I attributed it to possible water in the fuel and started adding a fuel additive to absorb the water. At first, it was only a couple times a season, but it became more and more frequent. On a couple occasions, I had to get towed in. By the time I got home to trouble shoot it, it ran fine. After searching the forums, talking to experts, I did all the things I've read about in the forums: changed the low pressure fuel pump, ECA and fuel pump relays, checked the fuel pressure at the injector rails, checked for blocked pickup tube or venting in the fuel tank, cleaned the connections to the inline 50 amp fuse, checked the kill switch, checked the electrical grounds, swapped out the ECA with one from another same model year boat, new distributor cap, plug wires, etc. As it became more frequent and definitive, it seemed to act like someone intermittently was pulling the kill switch. Finally, over the fourth of July, the engine quit for good and it would not run. It turned over fine, but no go. I had copied the PCM maintenance manual years ago and was able to follow some of the diagnostic routines, and had purchased an OBD1 code reader but no abnormal codes ever came up. What I really needed was the breakout box to completely diagnose the system. I found one on e-bay for $100 and began to go through the diagnostic routine in the manual. To make a long story shorter, I was getting power to the ECA relay, but no power to the ECA itself. This would indicate that the ECA relay was bad. I had already switched this out, and had four relays on hand. I kept getting the same fault. Certainly four relays couldn't all be bad! I tested all four relays by putting 12v across the appropriate contacts, and all worked fine. So even though I could measure a voltage to the relay, for some reason it wasn't tripping the relay. The power to trip the relay comes from the ignition switch, and I noticed that it was about 1.5 volts less than the battery voltage. Could there be some corrosion or bad connection between the ignition switch and the ECA relay? I traced the purple ignition wire from the ignition switch through all the connectors back to the engine, testing for resistance at each segment. The wire then goes to the accessory starter solenoid where another wire (brown) connects to the same terminal. This wire then goes directly to the ECA relay. There was a huge resistance across this segment. As I opened up the wire bundle, there is a diode (1N4001) between the solenoid terminal and the ECA relay, the purpose of which is to protect the ECA from someone inadvertently hooking up a battery backwards. I placed a jumper across the diode and Voila'. the engine started and ran perfectly. There are actually two diodes in parallel coming from different terminals on the solenoid. I just had to jump the one directly attached to the purple ignition wire. I asked my brother, an electrical engineer if diodes fail, and he said they do, but it's not all that common. Depends on the circuit. These diodes can be had for about 10 cents apiece. I splurged and bought five for 32 cents apiece, hoping they must be better quality. I now have 100 years worth of diodes. I ran the boat for a couple hours yesterday, and it runs perfectly. In retrospect, it all makes sense now. The diode was dying and intermittently wouldn't allow enough current to open the ECA relay, hence the surging, quitting, etc. Pulling the kill switch has exactly the same effect as it is wired directly into the ignition circuit. I hope this post helps others who have the same problem. Four years of headaches, hundreds of dollars in replacement parts, and many man-hours of work, all due to a ten cent diode
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BobinIL
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Posted: May-30-2023 at 7:30am |
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Well it ha been a while since I have messed with the boat. Put two new relays in it yesterday and took it to the water and same thing, It ran great for almost exactly 30 minutes then lost power and acts like it is not getting fuel. I am at my wits end with this thing
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KENO
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Posted: May-30-2023 at 8:05pm |
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When it loses power, are both fuel pumps running?
I suppose it's kinda hard to tell if the HP is running but you should be able to feel the casing on the LP pump and see if it's abnormally hot or a normal temperature. Your pressure gauge that I think you already have should tell you if both pumps are running and putting out normal pressure (31 plus or minus 3) at idle, and 39 plus or minus 3 at full throttle and somewhere in between those numbers at part throttle It seems like you've been through the whole fuel system fairly recently but I figured it was worth asking again this time around
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MrMcD
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Posted: May-30-2023 at 9:19pm |
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What about the check valve on the fuel tank vent? Anti Siphon valve I think the name is? If your tank does not vent you eventually build up a vacuum and no fuel flows. Many have had the issue with both carbureted and FI boats. I feel your pain and hope you find the solution and share it.
Any chance there is something in the tank that is loose and floats to your inlet blocking it off but floats away once the suction from the pump is shut off. Like you, searching for the one thing not yet found.
Fuel Pressure dropping off at least puts you on a straight path to repair. Mark
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Morfoot
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Posted: May-31-2023 at 6:08am |
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+1 on what Mark said and to add to that. Have you checked the fuel tank vent on the stern of the boat for blockage? Pollen, spiders, mud daubers may have blocked the vent so the tank can't "breathe".
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"Morfoot; He can ski. He can wakeboard.He can cook chicken.He can create his own self-named beverage, & can also apparently fly. A man of many talents."72 Mustang "Kermit",88 SN Miss Scarlett, 99 SN "Sherman"
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KENO
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Posted: May-31-2023 at 7:14am |
I think maybe somebody is a little mixed up about where the anti siphon valve is located and what it's purpose is.. Bob has checked/cleaned the anti siphon valve valve and suction screen before in this saga. (old posts here and on PN) Got an in line filter between the tank and the low pressure pump? On the electrical side of things............the diode mentioned earlier might be looking more and more like a possibility. I don't think anybody wants to blame it on the ECM yet
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BobinIL
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Posted: May-31-2023 at 9:57am |
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I have done so many things to this boat sometimes I have a hard time remembering all that I have done. I do believe that when I had the tank out and cleaned it out I checked the pickup tube screen and the check valve. Luckily a good friend of mine that has a marina on a private lake used to be strictly Matercraft dealer picked up a Nautque franchise a couple years ago. He is fairly close and can water test boats at will. I am taking the boat to him to try and figure this out. He is going to start by running it on an auxillary tank of fuel to cancel out any fuel line/tank issues. then we will check power to both pumps while acting up. I am starting to suspect a possible bad oil or temp sensor could be causing it to go into limp mode. Not sure though because the dash alarm doesn't come on.
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KENO
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Posted: May-31-2023 at 12:27pm |
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If you think it's going into liimp mode it's pretty easy to disable the limp mode
i suppose first though, does the dash warning light come on when you turn the key to the Run position? It should to tell you that the light bulb and the circuitry are functioning. When you go to start, the light would go off as soon as oil pressure is above 5 psi. If your oil pressure gauge and water temperature gauges are functioning and reading normal, you can disable limp mode by lifting a couple of wires You disconnect the tan/black wire at the oil pressure switch that's right next to the oil pressure sending unit and disconnect the tan/black switch from the temperature switch (intake manifold behind thermostat housing) and tape the ends so they don't touch anything else They probably both have a little black woven sheath covering the wires You don't remove any wires from the oil pressure sending unit or the water temp sending unit, just from those 2 switches, that way you always have oil and temperature indication With the wires removed it can't go into limp mode So you lift the wires, go for the obligatory boat ride and see what happens Here's a thread in the link with some info |
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TRBenj
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Posted: May-31-2023 at 1:59pm |
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Is there not a knock sensor that can trigger limp mode as well?
I have never triggered limp mode on a GT40, but the older Protec version doesn’t really act as described- it’s a pretty hard limit of 2500rpm- and it isn’t smooth. |
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KENO
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Posted: May-31-2023 at 7:48pm |
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I think the knock sensor is in it's own category separate from limp mode.
Here's PCM's description of the knock sensor function  Easy to disable the knock sensor, just pull the connector off the terminal, no tools needed. It's at the back of the cylinder head behind #8 cylinder with a black and green wire and a push on connector. Engine runs just fine without it, but you have no knock detection or protection from knocking. I've never had the joy of a knock sensor going into action at 4000 RPM or so and don't really want to either I'd disable the knock sensor separately from disabling the limp mode function. Here's the limp mode description A gt40 spits, sputters and runs like crap when it goes into limp mode till RPM's are low enough  |
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BobinIL wrote: