Vapor lock?

[bwana50]

Boat: 1996 SN Engine: GT-40

Situation: Went out boating today; we drove around for an hour or so with no problems. Parked the boat, went to lunch for about 1.5 hrs. When we returned, the boat started and we idled around for about five minutes. When I pushed the throttle forward, though, the engine sputtered, died and refused to start. This evening, after we'd been home a few hours, I tried again and it started.

Question: Could this be vapor-lock? I admit I have done no troubleshooting yet, but that's what it seems like at first glance. I didn't even have the presense of mind to listen for the pumps while at the lake. My understanding is that these boats don't have a fuel pump in the gas tank to pressurize the line; both pumps are at the front of the engine? The fact that it now starts, when I've done nothing to it, seems to me to rule out ignition problems or bad relays. Any ideas on things I should check?

Tim

[wakeboardin2k4]

RE: Vapor lock?

Ya, you can rule out electral problem in your ignition system and focus on fuel. You are correct that the electric fuel pumps are located on the front of the engine. You should be able to hear the electric pump turning on for your motor when you turn the key into the on position.

Your description sounds like a vapor lock situation. I believe the procedures for vapor lock is to inspect your fuel system and cooling system. Check your fuel lines and check for leakage, and water that could be getting into your fuel lines. When was the last time you changed your impeller and thermostat? Check for leaks from all your hoses coming from your raw water pickup all the way to your exhaust manifolds. Make sure none of those tubes are leaking. If your impeller has not been changed in a long time I would check that because if your not getting adequate water circulating you can overheat which is a cause of vapor lock. Did you happen to look at your temp gauge on your dash? When was the last time you changed your fuel water separator? Or at least drained the water out of the existing one? That was a cause of my vapor lock issue this summer. Also bad gas is possible depending on where you filled up or how long its been since you ran the engine.

Other than that I'm all out of ideas of what could be causing your vapor lock situation.

[bwana50]

RE: Vapor lock?

Still working on this issue. Thus far I haven't been able to duplicate the problem when I have tools around for troubleshooting. I was able to simulate the problem by disconnecting the LP pump; the engine ran for about 15 mins before dying that way. That seems a bit longer than it usually takes for the problem to show up on the lake, but it was just idling.

I do know that:
- Cooling system is good.
- When the problem occurs, LP pump is running. Can't vouch for the HP pump, as the LP pump is louder and drowns out HP sound. I think this rules out the relay, as I believe both pumps are powered by one relay.
- Pressing the shrader valve with a knife tip (my very unscientific fuel pressure test method) produces mostly air.
- I tried blowing into the fuel line from the tank, with no results - is there a check valve in the line? (Note: this was not while problem was occuring.)

I doubt it's bad gas or water in the system, as that would cause problems all the time (or nearly so), not just on warm re-starts. I haven't completely ruled out ignition, but haven't been able to check that during an "episode" yet. At this point it appears to be fuel starvation possibly due to HP pump, vapor lock, or other blockage. Any other ideas? I'm now carrying an extra toolbox of diagnostic equipment on the boat for the next time it happens. I'd rather find the problem before throwing new parts at it that may or may not work.