Intermittent problems are the most difficult to diagnose. I assume you are not getting any alarms since you did not mention it. If you have a four-light key switch (oil pressure, overheat, alternator, and check engine or MIL) then you need to check for any fault codes by shunting the service connector. That procedure has been described many times on this forum. If you need a write-up of the procedure, send an e-mail to me at
[email protected].
From your description it sounds like a fuel feed problem, so the following is a recommended set of simple and easy things you can check and do.
1. If you have an external Racor-type fuel/water separator, put in a new filter element. They should be changed out annually.
2. Pull your onboard fuel-water separator, dump the fuel in a clear container and check for water and debris in it. If there is any deterioration of the filter element, replace it.
3. Run your engine with cover off and observe the level of fuel in the low pressure fuel filter. It should be over 2/3's full while engine is running. If that filter has not been changed within the last year, change it.
4. Drain the VST. If you need instructions, send me an e-mail.
5. Replace the high pressure fuel filter.
After doing these things, take the boat out for a run and try to repeat the problem. If it does start to stall out, first open the fuel tank cap and see if that alleviates the problem. If so, you have a clogged breather tube to your fuel tank. When the engine is trying to stall, feel the pump up bulb on the fuel line to see if it is partially collapsed. If so, one possibility is that the check valve in the pump-up bulb has failed and is blocking fuel flow. The other possibility is that the pick up tube in your fuel tank is getting clogged. You will need to remove the pick up tube to see what the problem is and you will likely need to drain your fuel tank to get the debris out of it. If the pump-up bulb is not trying to collapse, pump it several times while the engine is trying to stall and see if that improves the engine performance. If so, it is an indicator that you may have a failing low pressure fuel pump.
If none of this works, come back at us and document each thing you have done.