1999 7.4L Mercruiser with Vapor Lock problem


Hello, I have a 1999 Chapparal with a 7.4L MPI engine. My engine has only 135 hrs since I do not feel compfortable taking the boat out very often. When I take the boat out, it runs greate. Than afer driving around the lake a bit, we go to the sand bar for 1-3 hrs. When I start the boat, it starts for about 15-20 seconds and then cuts off. It will not restart. I hook up a fuel gauge to the schraeder valve and notice noi fuel pressure even though I can hear the fuel pump cycle on. I drain off the fuel and see a lot of air in the line. It ussually take about 20-30 minutes of just tuning the key and cycling the fuel pump. I prime off the air bubbles. Then all of a sudden the fuel pressure raises to approximately 37 psi and the engine starts. It runs great after that till I turn it off again.

I normally do not have the issue if I let the engine sit overnight. It only occurs after running the engine during the day, stopping for a few hours, and then try to restart.

I have been experiencing this issue for about 4 years. I did have my engine removed about 4 years ago due to a bad winterizing job in which 3 brass plugs popped. Ever since this I have been experiencing this odd issue. I have replaced the anti-siphon valve, put on a new 160 degree thermostat, new water pickup/pump, replace the fuel water separator, check to make sure my tank is ventilating properly, yet I still have experienced this issue. The fuel water separator is on the lower left side of the engine and the water cooled fuel pump is on the lower right hand side of the engine in a location that is impossible to reach without removing the engine. The fuel line runs somehow under the engine which is impossible to view without pulling the engine.

My latest idea is that this may be caused by bad routing of the fuel line under the engine. Could this cause vapor lock? Does anyone know if this could be the issue? I hate to pull the engine just to check the routing and then later find out that I should have replaced other parts. I really do not want to replace an expensive fuel pump if it is not the issue.

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