Bypassing mechanical fuel pump with an electrical one

[Nekton73]

Although not the same animal, perhaps my mechanical to electric fuel pump conversion for my Atomic 4 will provide some relevance.

Similar situation, removed mechanical pump and installed blank, replaced with low pressure electric pump (4psi I believe, can't remember, purchased from NAPA), and wired via an oil pressure relay switch so that the pump will only receive power when the ignition is on and oil pressure is being produced by the cranking/running engine. If oil pressure is lost then fuel flow stops. Perhaps not as big a concern with diesel but with gasoline an important safety precaution.
Removed the mechanical pump because without fuel flowing through it to lubricate and cool it the diaphram would eventually break down. Unknown how long that would take, but it was recommended as part of the conversion. Old mechanical pump rebuilt and stored on the boat with appropriate fittings so that if electrical fails I have a spare.

[JimZeigler]

I've installed a small diesel fuel pump on a polishing system on my trawler. It was a "reefer" fuel pump similar in size to the electric fuel pump feeding the 3 cylinder Universal diesel on my older Catalina 34 and the 8 kW Westerbeke genset on the trawler. All have worked fine for me.

[Shaneesprit]

Originally Posted by Esargent6

Good afternoon. We are here in la Paz having just arrived from Mazatlán. Before leaving Mazatlán we had trouble with the mechanical fuel pump on our yanmar 2GM, so we installed an electrical one, while leaving the mechanical one in place. We now notice fuel leaking out of the mechanical one. It looks like we are not going to be able to find a replacement for our mechanical fuel pump right away so we are thinking about removing the mechanical one entirely putting a plate over the hole and just going all electric. Now we did have one electrical fuel pump(original yanmar electric fuel pump purchased in Mazatlán) go out on us doing the crossing and we had to go to our backup which is an edelbrock with a psi of 4-7. Has anyone done this before? Any thoughts? Thanks in advance for any input.

No point in having 2 inline fuel pumps you are just doubling your chances of a failure, that you are now experiencing.
Fitting an electric pump means removing and blanking the mechanical pump.

My electrical pump failed causing air to get in the fuel system, I removed the Electrical pump and replaced it with nothing. Now I have no lift pump and my engine is quite happy and more reliable for it. ( Engine is Beta 25hp and tank not far from the engine.

[fox9988]

You can cut the "lever" off the mechanical pump and reinstall it as a blanking plate.

[Ballsnall]

Originally Posted by Esargent6

Thanks again for the input. How long did it take before the diaphragm broke down? I kind of figured that we would eventually have to remove the mechanical pump completely but I’m just hopeful that it will get us to penasco from la Paz before it goes out.

If your bypassing the mechanical pump then it's because the diagram is already holed. This is by far the most common reason for failure, very occasionally it's the non return valve.

Take the fuel lines off the mechanical pump to prevent fuel entering the oil sump and if is not leaking oil you should be fine to run it like that for a while.

A repair kit for the mechanical pump is cheap and it will be good for many more years of reliable use.

[jamhass]

Originally Posted by Esargent6

Hopefully I have hit pay dirt. After going to every possible marine supply place in la Paz, Rob and I believe his wife who have a mechanics service business right next to the cruiser supply at la Paz harbor think they might have if not a new mechanical fuel pump maybe a used one or a lower psi electrical pump for my 2GM. They also had the impeller that I use for my water pump to replace my spare that we had to install during our crossing. Thanks all again.

Rob Cross (and Kim, Cross Marine) are THE GO-TO place in La Paz for engine work. Trust their recommendations and you will be fine.

[skipperpete]

On most of the small diesel engines that I encounter on yachts , the fuel systems return very little to the tank due to either a return line orifice or a check valve that maintains pressure at the injector pump ( mostly for self bleeding) and with a mechanical pump, once that pressure is reached, the pump stops delivering and the lever stays high off the cam.... electric pump acts similarly but is stopped by an internal pressure switch. If you install an electric fuel pump and you can hear it constantly and rapidly ticking it means that there’s no restriction in the return and unless that pump is rated for constant duty it WILL burn out. This is most apparent on homebuilt fuel polishing systems that run continuously with very little resistance to flow. No problem if you have a good continuous duty pump, huge problem with many off the shelf cheapies.
Some engines have no return,most GM series yanmars are like this with just a leakoff line from the injectors... usually dry ....so any duty pump will work.
If you keep burning out fuel pumps try measuring the rate of return at the tank, if its high, there’s possibly a problem. Incidentally none of the above applies to common rail engines or any engine that uses fuel to cool the injectors (GM and Cummins)

[jsanton]

I just missed you. Left La Paz a couple weeks back.
I’m a brat. Fly up to TJ, cross the border at CBX, buy the Yanmar fuel pump, get a beer, and fly back. Airfare is cheap there and travel is fun!