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gt40 problem found- now what? |
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Don W 
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Joined: April-23-2019 Location: ga Status: Offline Points: 30 |
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 Topic: gt40 problem found- now what?Posted: September-16-2022 at 2:21pm |
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I have a 97 Nautique with the Gt40 engine. I have had a problem with the boat stating to surge and even die after hard sking for a bit. After many false diagnosis and parts (pumps, relays, MAP, etc) I have determined that the power to the low voltage pump goes out or is intermittent when this happens. I ran a wire from the battery to the poitive terminal on the pump after this started and it solved the problem. Now I need to find out what is causing this, and how to fix it All suggestions are appreciated.
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DON W
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11162 |
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Posted: September-16-2022 at 4:20pm |
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You may not realize it but if you're putting 12 volts to the positive connection on the LP fuel pump, you're also putting 12 volts to the positive connection on the HP fuel pump at the same time assuming your wiring is intact.
If you have the 301 page gt40 manual look at page 6-8 and 6-9 for the wiring diagram. You mention that you have it in an old post from a couple of years ago about the same? issue. If you have a broken wire between the 87 terminal on the fuel pump relay and the LP pump, killing power to just the LP pump, that's the only way your jumper would just power the LP pump when you install the jumper.. If you think that's the case, you'll have to dig into the wiring harness and follow the wire from the pump back to the 87 terminal on the fuel pump relay and verify continuity. Otherwise try another pair of relays and make sure the sockets they plug into are good and clean. Either the fuel pump relay or the ECM relay having an issue kills power to the fuel pumps so the best thing is to replace both whenever you're replacing one of them.
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Don W
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Joined: April-23-2019 Location: ga Status: Offline Points: 30 |
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Posted: September-17-2022 at 5:12pm |
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I disconnected the wire running to the low pressure pump to isolate it from the high pressure pump before putting on the hot wire. I am on about my 4th set of relays, but I ordered some more on line that are supposed to be the replacement for the originals. to be here tommorrow. They have a light to indicate power. I tested the pump and it puts out 16 ounces of fuel in about 8 seconds so its not the problem. (its also new). Thank you for your help! Vince at ski dim told me some Diodes in the GT 40 wiring harness had started giving problems. I don't know enough about that yet to check it out.
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DON W
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Don W
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Joined: April-23-2019 Location: ga Status: Offline Points: 30 |
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Posted: September-17-2022 at 5:15pm |
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DON W
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11162 |
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Posted: September-17-2022 at 6:30pm |
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I guess you should have mentioned in the first post that you disconnected the wire. You can do that or you can leave the original wire unhooked, taped over or cut from the LP pump and splice a wire into the HP pump supply wire and hook that to the LP pump and things should work the way they're supposed to. That would be both pumps getting power from the fuel pump relay with no temporary jumper. There are 2 diodes that are associated with the EEC power and keep alive circuit. A bad one in the power circuit will kill power to the ECM relay and the fuel pump relay at the same time and the engine wouldn't run. A bad one in the keep alive circuit will take away the power supplied to the ECM when the key is OFF. Neither of those would cause your issue. Look at page 6-2 of the big manual and find the parts labeled "12" , they're the 2 diodes If you want some reading on the diode problem, click on the link below So in other words there's not an individual diode that would only affect your LP pump. There's also a 3rd diode, it's in the SLOW circuit and won't affect your pump in any way. PS.........the colors shown in the manual and your wire colors may be different. The manual was originally for the OMC version of this engine which came before the PCM gt40. There are a fair amount of other differences too
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KENO
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Joined: June-06-2004 Location: United States Status: Offline Points: 11162 |
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Posted: October-03-2022 at 7:21am |
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Can't help but notice that it looks like you have the boat for sale on the "other" website (and maybe some other places too).
That kinda makes me wonder if you fixed things and if you're maybe gonna update this thread?
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