99 Sport Nautique GT40 runs for hours then just stops

[diamondjr]

I have been out on my 99 Sport Nautique for hours at a time the last 3 days. Boat starts and runs fine as we are on the water. Engine on/off while we change skiers and I have no problems. If I go back to the dock and let the boat rest for 30-45 minutes and head back out onto the water it will start fine but stalls about 100 yards from the dock. It has done this exact same thing 4 times. I can replicate this each time. Thanks for good neighbors and a tow, but this is getting old.

If I let her set for 3-4 hours I can go back out with no problems. Last time we stalled out I took the boat back to the dock and sprayed Sea Foam into the Flame arrestor to start the boat, but it will not continue to run. So I assume it to be a fuel delivery problem. But why would it work for hours at a time but if set to rest for 30 minutes or so I will stall out quickly once under power.

I am stumped

[bscott]

Could be one of the relays on the back of the engine getting too warm when the boat sits still for a short period of time. They are known to fail. I'm sure you don't want to throw money replacing parts, but they are relatively inexpensive to replace.

[srock]

I had that exact same problem with a fuel injected Malibu. It turned out that the fuel line would get hot and vapor lock when the boat sat hot for about 30 min. Note that the engine gets hotter than when running for a shot period after shut down. If I ran the blower or cracked the engine box a after shutdown (for maybe 10 min) I could avoid the problem. The fix was to add a short heat shield to a 5" section of fuel line that ran along the engine. Try opening the engine box and see if you can no longer replicate the problem. Let us know if it works.

[charlesml3]

You're describing a situation called Vapor Lock. It happens exactly as you described. When the engine stops, heat "soaks" around to different parts of the motor. Sometimes it's enough to vaporize the fuel in the line resulting in vapor lock.

-Charles

[Ran Shackelford]

I have a 1997 Nautique GT40 that does the same thing. I was searching for information on the subject and ran across your post and joined PlanetNautique Forum to hopefully correct this problem for both of us. I am not a pro mechanic by any means but I have done a lot of my own work over the years and I really want to get this issue solved. I am in agreement that it is vapor lock. I think the gas boils in the fuel rail over the engine and pushes air back maybe to the fuel pump. Lack of fuel pressure is the result of vapor lock as I understand it, There are a lot of automotive videos on Youtube about vapor lock. It seems to happen more often with engines with carburetors than fuel injection. Until I know I have it fixed I always lift the engine cover as soon as docked. I have been wondering if putting an external blower or fan on it would be enough to keep the fuel from boiling. As to fixing it, I saw a video where the guy put a check valve at the entry side of the fuel rail preventing loss of pressure. I am thinking this might be the solution along with as much heat shielding I can rig up. I hope this is helpful and sure would appreciate any tips or advice.

[zoah]

On the fuel rail there is a schrader valve. Get a gauge and put it on there. When you're having your starting problems confirm you're seeing 30+ PSI at the rail.

If fuel isn't the culprit you might have a bad TFI module on the distributor. Sometimes those get heat soaked and cut out.

[Seabrad]

Had the same issue with my GT40 in 1999 Pro Air. I have a EFI tech who lives next door and it’s been proven as we have gauged the fuel rail when hot and failing to start and confirmed good pressure, then go and tap the relay for the fuel pump and hear it click and engine will start. It’s the relays failing when hot..if you lift the engine hatch and let them cool off you’ll eventually get the same result..I changed them both out and never had the issue again.


Sent from my iPhone using PLT Nautique

[diamondjr]

Thanks for all the suggestions. I have put a fuel pressure test on the FCC and I am getting 37PSI but have not gotten the chance to replicate the problem when it will not start. Life has gotten busy and boat time has suffered for a bit. I will post my results when I get them so that anyone else with this problem will have something to reasearch.

[gun-driver]

You would want to check the pressure on the fuel rail also. There's another schrader valve up by the thermostat on the fuel rail.

You can see the brass adapter for my gauge behind the left of the distributor on my '95. Sorry about the sideways pic.

[MikeJ]

Zoah, can you point out the TFI module on the engine that gun-driver posted? I have an engine manual but it doesn't have any diagrams showing what things are and where to find them.

I'm a newby at this - any insight is most appreciated.

BR

[diamondjr]

I am still having the same issues as my original post last year. This weekend it came to a head again, but now I am not getting any fuel pressure at the FCC. Thanks to DanielC I did pull my low pressure fuel pump and did have a fair amount of debris in the mesh screen. I was hoping that once I cleaned that out cleaned all the vanes re-assembled thinking that my problem would be solved. But that still did not fix my issue.

When I prime the pump with the ignition the pump does spin but I kept the line off the FCC trying to measure the amount of fuel. Regardless of the number of times I prime the LPFP I don't get any fuel on the output side. I also tried this having the fuel input from a container of fuel to rule out an issue with the lines from the tank, and also to visually see if the pump pulls. IT does pull a little fuel from the container in the 1-2 second run but not enough to even push it to the output hose.

Pre-season I did pull my gas tank cleaned installed a new fuel pickup tube and confirmed that my anti siphon is working fine.

My only thought is that the LPFP is spinning but not pulling fuel and it is time for a new LPFP. Any other suggestions.

[charlesml3]

Yea. Replace the LPFP. It's not a terribly expensive part.

-Charles

[Neptune442]

Carter P4389 from rockauto.com

https://www.rockauto.com/en/moreinfo...sn=262&jsn=262

[DVskier]

Low pressure fuel pumps are prone to failure on GT 40’s. Not terribly expensive and should provide at least 10 years of service.

[diamondjr]

Well I thought I would report back when I had things working again. It seems that this type of problem typical and there are lots a lot of answers. Each problem is different but this is what I believe my problem was.

I ended up putting in a new LPFP hooked it up but still it would NOT not pull any fuel from the tank. No pressure in the FCC. I then put a hose on the input of the LPFP and into a 5 gallon gas can. Unhooked the output from the FCC and put that into another can. Cycled the new LPFP and boom I had fuel. Hooked the output back onto the FCC and started the boat with the 5 gallon can. She started right up. Ran the boat off the can for a bit. Now I knew that I had an issue towards the tank. Took off the Anti-Siphon and sure enough the boat would run. I had previously cleaned and felt that the Anti-Siphon was OK the spring and bearing looked and moved fine. But there still must have been something that was causing issues.

I believe my problem was a bad Anti-Siphon and a LPFP that was at the end of its life. I have had her out now a few times and she is no longer stalling after she gets warm.

Hope this helps someone else!