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Boost fuel pump


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Hello I'm new to the forum. I recently acquired a 1994 malibu echelon with a 454 mercruiser efi. My question is I've been having some vapor lock issues when motor heat soaks. So I've installed the low pressure fuel boost pump kit that mercruiser sells. Its before the water separator filter will this pump work in conjunction with the mechanical fuel pump or do I need to bypass it? 

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It is uncommon to experience vapor lock with a mechanical fuel pump as compared to using an electric pump.  The low pressure fuel boost pump is designed to be used on fuel injected engines that only have a high pressure pump, not on your application.

Some things that help reduce vapor lock on carb engine applications are:

. Reduce the length of fuel supply hose from the fuel tank to the fuel pump as much as possible and limit the number of bends in the hose.

. Make sure the anti-siphon valve is not clogged and it is working correctly.  Limit the amount of restrictions on the fuel supply hose.

. Increase the inside diameter of the fuel supply hose using a larger hose and fittings.

. Keep the engine compartment temperature as cool as possible and make sure it has adequate ventilation.

. Keep the pressurized fuel line from the fuel pump to the carb away from heat sources.  If it is a metal line, consider replacing it with a USCG approved pressure hose like this:

https://www.westmarine.com/buy/sierra--8-8114-fuel-line-hose-universal--10505360?recordNum=15

 

Edited by csleaver
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Well it has a mechanical pump and a vapor separator tank with electric fuel pump inside. The engine is electrictronic fuel injected 

Edited by West94
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Sorry, due to the age I assumed it was a carbureted engine.

That looks like the original low pressure mechanical fuel pump in the picture. 

Some of the early fuel injected Mercruiser engines had a mechanical low pressure fuel pump that was mounted to the belt driven sea pump and supplied fuel to the VST where the high pressure pump is.  The sea pump housing where the fuel pump is mounted had a small cam shaft to actuate the pump arm and was filled with gear lube from a fill / drain screw.  I have often found this reservoir filled with fuel when a fuel pump fails.

Does that sound like what you have on the engine?

If you remove the mechanical fuel pump, you will need to replace it with a block off plate.  Something like this will likely work.

https://www.summitracing.com/parts/sum-402035/make/chevrolet

 

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Yes that is exactly how mine is the low pressure pump is mounted on the raw seawater pump. It looks new. So I just left it all plumbed the same and installed the a low pressure pump back by the tank and its running flawless so far. If I did away with it and used a blocker plate I'm not sure what I would do with the clear line that runs from the vapor tank to that mechanical pump is that some sort of vent?

Edited by West94
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That opaque hose on the fuel pump is there to prevent a faulty mechanical fuel pump with a torn diaphragm from pumping fuel into the bilge.  Instead, it would fill the VST or drain into the intake manifold to prevent a potential fire or explosion.

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