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Old 18-01-2012, 22:29   #1
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Okay Diesel Geniuses - Riddle Me This (re: Fuel Pump )

Yanmar 4JH2E

So one of the fuel bowls hasn't been used in a long time, so I removed it entirely and cleaned the hell out of it. Pictured here:



So I get it cleaned, drop a new filter in, and switch the handle over on the dual Racors to point to the now bone-dry filter. I loosen the bleed nut (on top of the secondary on-engine fuel filter), and get ready to click the little bleed lever about a billion times. Yeah, I know I could have poured some diesel in and sped up the process but no one has ever accused me of being smart.

But then I remembered that I hear a pump kick off when I put the key in the "on" position. So I pop the key in, put it to "on", and sure enough the little bowl starts filling up. I wait a little longer and see the bleed nut start to rattle. I turn the key off, tighten the nut, and BOOM, engine started up no problems.

tank -> corroded little pump that goes on with the on switch -> dual racors -> big grey spooky yanmar
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Old 18-01-2012, 23:09   #2
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

So what exactly are we supposed to riddle out?
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Old 18-01-2012, 23:11   #3
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

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So what exactly are we supposed to riddle out?
What the heck is that pump doing? Seems like it shouldn't be able to pressurize all the way to the nut like that.
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Old 18-01-2012, 23:12   #4
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

Yeah riddle what? There must be a pump in the tank or the line?
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Old 18-01-2012, 23:13   #5
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

Why not? If it doesn't have excessive lift it should be able to pressurize all the way to the high pressure injection pump. A lot of people use an electric lift pump so they don't have to bleed a system. I've also seen people install fuel bulbs that you can pump by hand to do the same thing.

So long as there are no air leaks and the lift isn't excessive it should be able to do that, no problem. =)
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Old 18-01-2012, 23:15   #6
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

Also in some setups if fuel line goes over the lift capacity of the mechanical fuel pump on a motor a manufacturer will recommend installing the electric pump to aid in the low pressure side of the system. This is commonly wired to the "ON" position of the switch.
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Old 18-01-2012, 23:18   #7
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

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Also in some setups if fuel line goes over the lift capacity of the mechanical fuel pump on a motor a manufacturer will recommend installing the electric pump to aid in the low pressure side of the system. This is commonly wired to the "ON" position of the switch.
Interesting.

So I'm reading through some threads where folks are saying the lift pump should be after the primary filter (tank-> primary filter -> lift pump), but mine is in line before the racors (tank -> lift pump -> primary filter). How much of a big deal is that? Just a potential for gumming up the lift pump?

one more:

How much of a difference is there between a generic low pressure fuel pump and a lift pump? Are they the same thing? Are lift pumps made by the manufacturer? Mine looks like a corroded ball of garbage and I'd like to replace it if it's not too expensive, or at lease have a spare ready to go.
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Old 18-01-2012, 23:25   #8
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

Nothing too mysterious there. The electric pump was probably installed by someone who didn't want to use the manual pump, and it is well placed to help bleed the system should you have an air leak. May even bleed the engine itself.

One suggestion: Have a spare electric pump stashed somewhere handy, and some hose as well. These pumps typically have internal check valves, so if the pump fails, which it will, the head pressure may not be enough to get the fuel to the mechanical engine pump.

Little rusty pump breaks=no engine. If she ever goes all hard starting on you, one of your first diagnostic steps should be to pull the fuel line off the inlet side of the mechanical pump, and turn the key on. No fuel? Bad pump.
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Old 18-01-2012, 23:27   #9
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

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Interesting.

So I'm reading through some threads where folks are saying the lift pump should be after the primary filter (tank-> primary filter -> lift pump), but mine is in line before the racors (tank -> lift pump -> primary filter). How much of a big deal is that? Just a potential for gumming up the lift pump?

one more:

How much of a difference is there between a generic low pressure fuel pump and a lift pump? Are they the same thing? Are lift pumps made by the manufacturer? Mine looks like a corroded ball of garbage and I'd like to replace it if it's not too expensive, or at lease have a spare ready to go.
1). It is better to have the pump after the primary filter but it isn't the end of the world if it isn't. Some electric lift pumps have filters built into them that can clog and that would just be another place you'd have to check if you had fuel problems. Better after the primary but not dire. I'd move it when you replace it one day. Try to get one without the internal filter.

2.) The pump you have is an "electric low pressure fuel pump". Most people just call it a "lift pump" since its giving your fuel a boost on the low pressure side of the system. The "low" pressure side is everything from the fuel pickup in the tank all the way to the injection pump which converts low pressure to high pressure. Your motor has a mechanical low pressure pump on it as well. This is the little guy you have to "click click click" to prime if you don't use the electric pump. I've heard both of them referred to as "lift" pumps.

3.) The pump is almost certainly not made by your engine manufacturer. They're common all over the world and you can pick them up just about anywhere at an auto parts place for between 50-100 bucks. Any electric (12v) fuel pump putting out low PSI would work.

Hope that clears up some of your questions.
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Old 18-01-2012, 23:28   #10
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

As a side note, I'd check and see if your engine can run without the electric pump at all. In most cases this would be true and the pump was installed as a convenience. In the event you did not have a spare you could just route around it.
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Old 18-01-2012, 23:31   #11
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

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Yeah thanks man, I think I get it. I actually have a spare low pressure fuel pump for another application just sitting around, and the guy who wired in the corroded ball of garbage one did a TERRIBLE job on the wiring (two green wires run in the pump, that's it, and the connections are "sealed" with electrical tape...).

I've just been learning diesels as I go, but some of the add-on stuff that isn't covered fully in the yanmar manual is a little confusing.
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Old 18-01-2012, 23:36   #12
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Re: okay diesel geniuses, riddle me this (re: fuel pump)

No problem man. Enjoy your blog a lot, glad I could help.
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