1995 Cobalt 220DP Volvo Penta Duall Prop 5.7Gi

[MERK2.3]

I am a profressional Automotive Technician and I am having a heck of a time with this boat. Tow it to the lake and it fires up and runs beautifully. After running the boat for about 30 minutes the kids want to jump in and swim. Shut the enigne down and sit and play to 30 to 45 mintes. Love the lake! Go to start up and the engine will start and idle fine for several mintes and dies. Will not run up on power for more than 15 or 20 seconds and acts like it runs out of gas. The engine acts like a vapor lock condition. Cranks fine, has spark, has injector pulse, but only 'vapor' out of the injectors and the fuel filter is almost empty when checked. I can bypass the fuel pump relay and get the system to prime again but it takes a much longer time then i would expect. After the system is 'full' of fuel again the engine will start and idle for a short time but will not come up on power without acting like it runs out of gas. The engine has a new fuel line from tank to the low pressure pump, fuel filter, new low pressure pump, all tune up parts, and the 'high' fuel pressure is correct. Vapor lock is my only guess. Can there be a problem with the belt driven water pump that will not circulate enough water to keep the fuel cooler manifold at the back of the engine to work correctly? Also, after restarted the engine temp is close to 200 degrees and will not cool down when it idles for several mintes. Stays above 175 and does not cool down at idle. Can the belt driven sea water pump on these engines cause any concerns like this? Any help would be great. I am running out of ideas.

Thanks to all.
I am new to this site and have enjoyed all the posts I have read.

 

[dypcdiver]

Re: 1995 Cobalt 220DP Volvo Penta Duall Prop 5.7Gi

Sounds like a fuel pickup problem at the tank. When you replaced the fuel line did you take the pickup out of the tank and clean it? Also on some systems there is an anti syphon valve that can malfunction. There should also be a vent on the tank to stop it building up a vacuum, try removing the filler cap when having difficulties and listen for a vacuum. As far as the belt driven pump I assume you mean the raw water pump rather than the circulating pump which is also belt driven. The impellers on these need changing every couple of years or any time the boat has sat unused for a long while.(the vanes distort and lose their flexibility).
By the way for future ref please include your full engine details and ref number from the tag on the engine.