350 mag stops running

[Rob 8043]

I have a 350 mag with a fuel injection engine. Boat has run fine for over 15 years, and all of a sudden I am experiencing a problem that I was wondering if someone else out there might have dealt with.

I boat in the desert heat, at Lake Mead. A few weeks ago I went out, and when I was pulling a water skier, the engine suddenly died, as if it lost fuel. After a few minutes, the boat would start and run and then the same thing happened again. Took it to a mechanic who checked everything and could not find an obvious problem, so he changed all fuel filter, water separator filter and an anti-siphon valve in the fuel line. Told me to take the boat out again, which I did yesterday, and this time the boat started right up, and it idled for several minutes in the bay waiting to pick up our passengers, and then I didn't make it out of the wake zone when the engine dies when i shifted out of neutral and slowly accelerated. Waited about 5 minutes, and it started again.

I'm calling the mechanic back on Monday, but any thoughts or insights would be most appreciated. Thanks in advance.

Rob

 

[alldodge]

Is it EFI or MPI, and how about a serial number or at least a year?
Need to check the fuel pressure

 

[Rob 8043]

1995 efi; my mechanic did tell me that he checked the fuel pump and it was ok?

 

[alldodge]

I just don't trust mechanics saying its OK, need to know what the pressure was read. Not saying the mechanic is, or is not any good but there have been numerous ones which were a mechanic in name only. From him changing parts out and not finding anything does not give me a warm fuzzy

Being a TBI the pressure should be 30 psi from idle to higher rpm. You have a VST which can create vapor lock issues, but this only happens after the motor is shut off when hot, then it sits for a while. There is heat soak on the fuel and vapor builds up, but your not having this issue from what I'm reading

If the fuel pump relay drops out, pressure stops and engine dies. Same thing can happen if main power relay drops out. Need to find out what is not happening when it will not start.

When you turn the key, do you hear the fuel pump energize?

 

[Rob 8043]

Thanks for your response. When I turn the key I believe I am hearing the fuel pump turn on before the starter engages. My mechanic thought it might be a vapor lock issue but based on what you describe, doesn't sound like he is on the right track. The problem only occurs when I am under power not after the boat has been turned off and sitting for a while.

 

[alldodge]

If you could get a fuel pressure gauge (local auto store loaner tool) and adapter (see below) to attach the gauge and see what pressure does


No 91-806901

 

[Rob 8043]

Spoke with my mechanic this morning, and he indicated that fuel pressure was checked and it was good. No codes on the computer, so I am bringing the boat back in, he did confirm that my problem is not a vapor lock issue, and he suspects there may be a relay that has gone bad. We shall see.

Thanks again for your assistance.

 

[Rob 8043]

I thought I would follow up with what I hope is the answer to my problem. Went back to the mechanic and he turned his attention to my electrical systems. It seems that I have a dual battery system, and one of the batteries was completely dead. Since I was told to always run the system on "all" the mechanic explained that the dead battery was drawing power which affected the EFI system which needs a certain level of current to run, and if amperage drops, the system shuts down. thinking back, I noticed this condition when i was idleing , but did it experience a shut down at WOT as well.

I am hoping that this explanation makes sense as I am once again heading to the lake to check it out.

Thanks again for everyone's input.

Rob