Bypassing mechanical fuel pump with an electrical one

[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.

[Ryban]

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.

What sort of electric fuel pump did you install? I've installed an electric pump to aid in bleeding the fuel system, and every one of them I've installed has failed on me -- I'm on my 3rd one and it has failed too. I'm guessing they either don't like being continually exposed to diesel, or having fuel flowing through them when not in operation.

[RocketScott]

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.

It's probably burning out because it's building pressure against the injector pump and there's not enough fuel going through it to cool it down. The mechanical pump is rated at .3L/minute @ 1000 rpm. The smallest Edelbrock diesel pump is rated at 2.4L/minute. It's trying to move way more fuel than needed with nowhere to go. Where you mount it may be a problem too. It pushes diesel better than it sucks. It needs to be mounted as low as possible in relation to the fuel tank

You could put a return line with a check valve on top of the filter housing on the engine to increase flow and decrease pressure. The feed pump is just there to get fuel to the high pressure injection pump. If the fuel tank were higher than the engine it wouldn't even be needed

All that being said. It's much better to get the mechanical pump working if you can. Less complicated, fewer things to go wrong, no reinventing the wheel. But if you're stuck you gotta do what you gotta do

[Esargent6]

Thanks so much for the input. The fuel pump that died was a yanmar P11039 FP31002T. The edelbrock which I’m assuming is rated at a higher PSI has worked but we have not used it continuously like we did the yanmar during the crossing. We have been able to run it for a while on the electric fuel pump and then disconnect it and the motor continues to run for about an hour before we have to go back to the electric one. What I have been told by a couple of different mechanics that any extra fuel the pump pumps is not a problem since it returns to the tank. But having said that we are getting a leak now around the old mechanical fuel pump. Do you think there is any advantage of removing the entire mechanical fuel pump and putting a plate in place of where it was which one clear advantage is we could fix the leak. If all we are doing is having to go through electric fuel pumps to make it to penasco I can live with that if we are not causing any additional problems.

[donradcliffe]

I'm surprised that you are having so many electric pump failures. Whole generations of Catalina engines were installed with only electrical fuel pumps, and breakdowns are rare.

https://www.pbase.com/mainecruising/...el_pump_filter

You can blank off the mechanical pump, but you better have a spare electric one if you want to go offshore.

[Ryban]

Originally Posted by donradcliffe

I'm surprised that you are having so many electric pump failures. Whole generations of Catalina engines were installed with only electrical fuel pumps, and breakdowns are rare.

https://www.pbase.com/mainecruising/...el_pump_filter

You can blank off the mechanical pump, but you better have a spare electric one if you want to go offshore.

That seems like a much nicer, proper, pump The ones I've had failures were cheap micro transfer pumps you see on Amazon a lot. They're great for other temporary tasks, like for polishing the fuel in the tank, but definitely don't survive in-line with the engine -- not sure why.

OP probably is using a proper diesel pump.

[Jim Cate]

IMO you need not remove the mech pump from the engine. Leave it in place, but disconnect the fuel lines from it and put them on the electric pump. With no fuel connection the old pump can not leak diesel and no harm will come to it.

Jim

[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.

[NorthCoastJoe]

As said above remove the lines from the lift pump and bypass it, no need to remove the pump.

On your electric pump pressure side put in a "T". Then run the leg of hose coming off the "T" up vertical about 24 inches then down into the fuel tank. The excess pressure will blow off into the leg of the "T" and return to the fuel tank. This will limit pressure to about 1 psi.at the pump, and keep fuel moving to cool the pump. Every 2 feet of head is about 1 psi with water, so diesel will be a bit less pressure, but in the ballpark for this job.

Another thing you could do would be a gravity day tank, Gerry can with a fuel line to the injector pump. With a 2GM 5 gallons would go a long way.

[Nineteen]

Hi,
I use one of these New Zealand made Fuelflow diaphragm pumps on our Yanmar 3JH3. Works a treat and they have excellent customer support. It pulls fuel through a Racor 500 and can be used to bleed or exclusively run the engine.

They don't corrode and are quiet.

Cheers Tom

https://fuelflow2020.nz/?page_id=184

[Tupaia]

Just a crazy thought. You have a cat - is the fuel tank above the engine? If so, you may not need a lift pump at all. Provided there is gravity feed you could just bypass the lift pump. It's purpose is to lift fuel from a lower position.

Leaks from fuel lines are mainly due to copper washers on banjo fittings typically used as connections to pumps. Either replace the copper washers or anneal them before reusing. Having an additional pump upstream of the lift pump will be putting pressure on these connections that would otherwise be under suction.

[Jim Cate]

Having an additional pump upstream of the lift pump will be putting pressure on these connections that would otherwise be under suction.

And thus eliminating those hard to find minor air leaks! Not a bad thing IMO.

Jim

[Bycrick]

Leaving a non-functioning mechanical fuel pump on the engine isn’t a good idea. Eventually the diaphragm will break down and crankcase oil will leak out. We ultimately had to take the pumps off and use a metal plate.

[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.

[Bycrick]

How long? Hard to tell? We were putting several thousand hours a year on the motors, but could never get the mechanics to keep the electrical system and hour meters working. But they all eventually leaked. We’re talking probably months not hours unless the diaphragm is already bad, causing the pump problem.