Mechanical Fuel Pump to electric

[customcar2boat]

Hello all. . I am in the process of swapping parts to a new 91 or 92 merc 4.3L longblock and I have run into a dillema. . My old engine had a mechanical fuel pump and my new block doesnt have a hole to run the mechanical pump anymore. . How do I go about converting to a electric pump and does anyone have any part numbers that might work. . I have found many out there but am not quite sure how they hook up to the carb . . Am i on the right track with this one.. . . .. MER861155A6. . I am stuck . . .

 

[customcar2boat]

Re: Mechanical Fuel Pump to electric

Is it possible to use an aftermarket fuel pump and get it to work?

 

[achris]

Re: Mechanical Fuel Pump to electric

Originally posted by customcar2boat:<br /> Is it possible to use an aftermarket fuel pump and get it to work?

As long as it's Marine Rated and you set up the oil pressure cutout switch correctly. That's so if the engine stalls the pump is shut off. Reduces the risk of 'KaaaBoommmmm!' (doesn't have the same ring as when Batman does it)<br /><br />And before anybody jumps up and down on my grave, Yes, I know I have mine disconnected, and so do some others here. Doesn't alter the fact that we have to advise you to put the switch in circiut.<br /><br />Chris........

 

[customcar2boat]

Re: Mechanical Fuel Pump to electric

Ok i am following to some extent. . Where can i find a oil pressure cutout switch? any help

 

[Don S]

Re: Mechanical Fuel Pump to electric

Let me explain this and show you a diagram. It's not an oil pressure cutout switch, it an oil pressure switch. It's like an on off switch that is worked by oil pressure. When the engine is not running and there is no oil pressure, the switch is off and there is no electrical power to the fuel pump, and if the engine should stop running for some reason, the oil pressure will drop to 0 and the switch will shut off again and the fuel pump will stop. As long as there is oil pressure, the switch is on and the fuel pump will run.<br />To start the engine, the power to the pump comes from the other small terminal on the starter. (Ignition termainal) and will put power directly to the fuel pump as long as the starter is engaged so you have fuel when starting the engine.<br />Here is a diagram of Mercruisers system I described. <br />#5 is the pressure switch<br />#6 is the pump<br /><br />PS: Most auto parts stores carry an oil pressure switch. It's a normally open (NO) switch that closes at 5 to 7 psi.<br /><br />

 

[customcar2boat]

Re: Mechanical Fuel Pump to electric

that is something i can deffinetly follow thanks don. . . one question i was considering. . . can it be done with a relay? I was possibly thinking using the coil as my on/off switch basically?

 

[Don S]

Re: Mechanical Fuel Pump to electric

No, the coil can't be the switch. The coil is live any time the ignition switch is turned to the on position.<br />A relay is not necessary as the fuel pumps don't require very much amperage to operate.

 

[Don S]

Re: Mechanical Fuel Pump to electric

BTW, Volvo uses a relay system and a diode, but not to the coil. The merc system is actually the easiest system to work with. Plus if you are ever on the water and the switch dies on you, all you have to do is hook the 2 wires together to get you home. But you also know you are bypassing the safety sytem and will be more aware. The Volvo system with the 2 relays and a diode is a real pain to jump to get you home.

 

[customcar2boat]

Re: Mechanical Fuel Pump to electric

that makes sense. . thanks. . i will work on it tomarrow and see what happens

 

[Destin]

Re: Mechanical Fuel Pump to electric

When I replaced my Mercruiser 5.0LX with a Vortec marine base 5.7L I used an electric fuel pump kit that had a oil pressure safety switch that was a SPDT. The common terminal is connected to the fuel pump positive, The NC contact is connected to the yellow/red start wire from the ignition switch going to the slave solenoid, the NO contact is connected to the purple ignition wire. When cranking with no oil pressure the pump runs from the NC start circuit. As soon as you get oil pressure the switch flips and closes the NO contacts running the pump from the ignition circuit. No need to run a wire to the starter. I mounted my switch on a tee with the oil pressure sender on the rear top of the engine where you can easily get to the wires. I hope it is OK to link to this site.<br /> <br /> http://ebasicpower.american-data.ne...wer&Product_Code=CARA68301&Category_Code=IND4

 

[Thompson66]

Re: Mechanical Fuel Pump to electric

I just completed this project three days ago. I Went down to GI Joes and bought a universal marine electronic fuel pump ( Perolator) but you can probably use any marine grade fuel pump ($45). Went to Knetchs Auto Parts and bought a three prong oil pressure switch ($6). On the three prongs there are three letters, P, S, I. Connect the I to the ignition, P to the pump, and S to the sender. In the open mode the pump shut off and in the closed mode the pump turns on. Thus, when the engine stop and loses oil pressure the pump will stop. Very simple.

 

[LubeDude]

Re: Mechanical Fuel Pump to electric

One more thing, you need to hard line all your fuel lines, stainless or steel. Use one flexable line to the engine, but it should be a made up line, use no screw clamps, then a hard line to the carb. If you dont, you risk a fire and the Coast guard will throw a fit.

 

[customcar2boat]

Re: Mechanical Fuel Pump to electric

Thanks for all of the input. . .<br /><br />LubeDude. . Do i have to run hard line from the tank through the fuel pump and them to the carb or cam i leave the flexable line from the tank to the fuel pump? and just hard line to the carb?? <br /><br />And one more question for all of ya'll. . my old pump had a hard line going to the carb and a tube out of the carb back into the fuel pump. . where do i connect the tube on the new fuel pump?

 

[Don S]

Re: Mechanical Fuel Pump to electric

You can use hose on the suction side of the fuel pump. (From the tank and hopefully a waterseperating fuel filter) But from the pressure side of the fuel pump to the carb needs to be steel line and double flared fittings which is what most pumps and carbs are setup for.<br />You can usually find a steel brake line of the proper diameter (usually 3/8" tubing) at any auto parts store. Get a tubing bender and make your line fit, then put a new flare on the end after you cut it to the proper length.<br />Use type A-1 fuel hose from the tank to the fuel pump and use the 1/4" wide stainless steel mini hose clamps to secure the hose and use hose barb fittings, not just pieces of pipe.

 

[seahorse5]

Re: Mechanical Fuel Pump to electric

There is also a Federal regulation that states the fuel pump must be within 12" of the motor if it is not installed on the motor.

 

[Destin]

Re: Mechanical Fuel Pump to electric

Download and save the revised (Nov 2003) fuel system regulations. Good reading.<br /><br /> http://www.uscgboating.org/safety/boatbuilder/downloads/FUELSYSTEM.pdf <br /><br />As far as I can tell, you no longer have to use metallic fuel line between fuel pump and carburetor.<br />Check out pages 63 to 73 of the Coast Guard's fuel systems regulations. It tells you the requirements for flexible fuel lines between the fuel pump and carburetor.<br /><br />Other revised regulations:<br /> http://www.uscgboating.org/safety/boatbuilder/downloads.htm