electric fuel pump installation

[HRHVT]

hi there, I guess I am about to change my manual fuel pump with an electric pump. I will be adding the oil pressure switch.
Question is, do i have to take out and plug up the hole for the old fuel pump? Also, can I just attach the new pump to the rubber line from the tank to the fuel pump? Splice it right in there, and still have the gas go thru the old pump?
If I need to run the fuel directly, then I will need to figure out how to attach the rubber line with the metal line which has the big nut attachment.

Thanks for your help

oh, with a 3.0l , mercruiser do i need certain gph? or any other details?

 

[bruceb58]

You would need to bypass the old pump. You need a 6PSI pump.

Why not just use a mechanical fuel pump?

 

[stonyloam]

In addition to the oil pressure switch you should use a fuel pump relay. The oil pressure switch is not designed to handle the current draw of the electric fuel pump. Pretty simple, you just wire the oil pressure switch to activate the relay instead of running the pump directly. You can leave the old pump in place ( bypassed) but it would be better to remove it an install block off plate over the hole.

 

[thumpar]

What is the reason for changing? Personally I would stick with the mechanical.

 

[HRHVT]

Well, i have another thread that is still not quite finished that goes into the reason for switching, but basically having trouble with fuel supply. I did actually switch to a new mechanical, and boat still does the same thing. A friend around town, who apparantly used to be a boat mechanic says that sometimes the (shaft) that rotates and activates the arm of the mech pump, sometimes gets worn down and they used to sometimes put a spot of weld on the arm to make it just a tad longer and have more ("pump". Or he said some people would just switch to an electric. I am at my wits end on how to fix this problem I have been having and almost willing to try anything.

 

[stonyloam]

Hmmmm... OK so you have installed a new pump and still having supply problems. The pump runs off of the cam, so unless the cam has been damaged the pump should be OK. Check the end of the pump arm, and see if you can see a smooth spot where it contacts the cam. If that looks OK then I suspect your problem is elsewhere. You need to check the anti-siphon valve at the fuel tank. It is a spring loaded valve and if it sticks can restrict fuel flow.

 

[HRHVT]

I did think about that, or that there may be crud or old gas in the fuel tank, so i disconnected the fuel line and put it right into a clean, good container with brand new hi test, non ethanol fuel.
I am about to change the carb, mine was pretty messed up, old, worn, etc, and got a good deal on a new rebuilt, or re-manufactured one so i will be installing that tomorrow.
meanwhile, it is just because my friend was mentioning about the pump. didn't make sense to me that the cam would get worn before the arm, but what do i know?

 

[thumpar]

Have you measured the fuel pressure?

 

[HRHVT]

no, did not have the equip for that, but when the engine faltered a little last time out, i put a little gas directly in the carb and it picked up a little. seems as though a fuel problem., but i didnt understand how that would happen with a new pump. unless it was a problem in the carb, which i think needed changing anyway, always ran rough, accelerator pump was not working, etc, etc

 

[thumpar]

That is why you need to measure the fuel pressure. You are just throwing parts at it without knowing what is wrong.

 

[stonyloam]

You can borrow the fuel pressure test kit from Autozone for free.

 

[fishrdan]

Harbor Freight has a fuel pressure gauge cheap enough too..

 

[RaceCarRich]

I seem to recall that too thick of a gasket or doubling of gasket could cause mech fuel pump issue. Did you use same thickness gasket when you replaced the mech pump?

 

[HRHVT]

They did actually send two gaskets, both the same. i thought it was just a weird mistake and only installed one of them, they looked to be about the same thickness as the one i pulled off. So, anyway, another problem I am having is that I have changed the 2 gas lines, the flexible one from the tank to the old (new) pump, and the one from the pump to the carb. However, when i bought the new hose from pump to carb, it came with a 5/8-18 threaded inverted flare end on it (male) and of course, so does the pump.
None of the parts stores or hardware stores around here seem to have a coupler. Any thoughts on that?
Can't seem to find one online either, or just not looking in all the right spots.
Thanks,

 

[bruceb58]

You may want to try Summit and/or just give them a call and they will know what you need.
https://www.summitracing.com/?gclid...1Hsa4M26EnoWbpaUgocq2aGDtBwvvJmmtDRoCLpjw_wcB

 

[HRHVT]

Thanks for the tip about Summit racing.
Even thought this is a pretty common part, it is not that common in VT I guess, and was easier to just have them ship it.
2-4 days