Intermittent 95 super sport nautique gt40 surge under load

[kylem03]

Hello all so as the title says I'm having an intermittent problem so it's challenging to re create and diagnose. When it happens, the Engine starts and idles fine and Runs well up to 2500 rpm or so then when I go to 3000 or more it will surge down like 3-400 rpms, recover, and surge again. I can give more throttle but this happens throughout the upper power band and won't clear itself up until I re start the engine. After I turn off the boat, and re-start its fine and we can wakeboard for a bunch of sets weighted with no trouble. This has happened on 2 or 3 occasions. I originally thought bad gas, I also checked the fuel filter that I replaced last fall and it is clean. I think it is electrical related to the fuel system but not sure where to start. Ecm and fuel relay would be a good first guess but after that, what? Anything else I should be checking? Thought about anti siphon and fuel pickup but that doesn't seem to make sense given I can restart and clear the issue up. Engine had a full tune up last summer (cap rotor, plugs, wires). When my fuel filter was replaced my high pressure pump was whining but the new filter solved it so I do t think it's a fuel pump issue.

Thanks for for your help!

kyle

[Bhenry27]

I have the same boat and same problem however, mine does not reset under restart. Any help on this would be great. It's been a really hard problem to troubleshoot.


Cheers!

Brett

[kmarine]

The Slow mode you are referring to is caused by the oil pressure switch brown wire with a black stripe. this wire is #24 wire to the ecm. this wire runs from the ecm through a diode and then splits into two wires both brown with black stripe. In the event of overheat or low oil pressure the wire grounds out sending the engine to SLOW mode. In slow mode the engine will run normal under 2500 RPM it the throttle is ran over 2500 the computer changes the timing and alters the fuel injectors to keep the engine from further damage. These sensors are independent of your gauges. To test remove both of these Wires, the oil switch is behind and under the fuel control cell. You can then trace the wire back to find the other sensor where they split. After troubleshooting replace the appropriate sensor. Most likely to fail is the oil switch. I spent two years and paid three dealers for service before I found this out with help from a mechanic from Ford. The computer does not store these codes, so a test computer will not detect this issue.

[2001SAN]

Does the check engine light come on at the same time? SLOW mode should trigger that as well.

D.

[kmarine]

That depends on the boat. Mine (1996) does not. I have never seen a check engine light, only a temp light that is attached to a different sensor. The newer computers may have one I have had every sensor replaced in mine already, never seen a light.

[Bhenry27]

Thanks kmarine, this is something I have not looked into. You referred to two sensors but only mentioned the oil pressure switch. Are they both oil pressure switches and the same? This is what I found on Nauttique parts. https://www.nautiqueparts.com/produc...nd-gm-to-2006/

thanks for the hope

Brett

[kmarine]

according to the service manual one brown wire with black stripe goes to oil switch the other a temp switch. On the oil pressure side the switch goes to computer the other is the oil pressuer gauge goung to dash sensor. Do not interchange these wires or it will not work correctly. yes the part you highlited is the oil pressure switch I am talking about #ro20015A

[Bhenry27]

so i got in there and i found oil switch #ro20015 (linked below). it appears i also have a oil pressure sending unit. that could be part of the problem? It does reference to being able to use the #ro20015A on all GT40's. I'm wondering what would be the correct switch to go with? Also since i have the oil pressure sending unit i linked below, i will plan to replace that as well.




https://www.nautiqueparts.com/produc...-tec-and-gt40/

https://www.nautiqueparts.com/produc...-2006-r020001/

[Fgroce]

For a test you can unwire and tape off the ends of the wires and see if problem goes away. Remove the wire from the pressure switch and the temperature switch. Boat is not skipping under 2800 rpms is it?