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Old 07-07-2021, 17:21   #1
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Yanmar fuel pump leak

I have a 1998 Yanmar 4JH2E, although I believe my issue crosses many models. I have been suffering for a year now with air leaks in the fuel line.

Early on, I replaced the line between the lift pump and the injector pump with clear fuel rated tubing. This allows me to see air bubbles.

I have chased many perspective areas. All unsuccessful.

Recently, I noticed that when I run the auxiliary electric fuel pump, I have leakage at the engine lift pump. I removed the suction side line, cut off half an inch, and reinstalled it. No change.

So yesterday, I moved the suction side line from the engine lift pump directly to the injector pump, and I now use the electric pump as my primary engine pump. The engine runs like a champ!

To me, it seems I have a failure in the lift pump. It is not easy to see, will not be easy to remove, and since we are on an extended cruise, I can't take the engine out of service while I inspect, and order parts.

Has anyone ever had problems with these pumps? Is replacing the pump a likely solution? Is there something that tends to fail that can be replaced? In other words, does anyone have any wise insight into the Yanmar lift pump?

Thanks!
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Old 07-07-2021, 18:01   #2
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Re: Yanmar fuel pump leak

Quote:
Originally Posted by sailingharry View Post
I have a 1998 Yanmar 4JH2E, although I believe my issue crosses many models. I have been suffering for a year now with air leaks in the fuel line.

Has anyone ever had problems with these pumps? Is replacing the pump a likely solution? Is there something that tends to fail that can be replaced? In other words, does anyone have any wise insight into the Yanmar lift pump?

Thanks!
How’s your oil? The diaphragm can fail. I haven’t replaced one myself. The remove/replace procedure should be straight forward. You replaced fuel lines, and being the primary pump, your close.
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Old 08-07-2021, 07:39   #3
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Re: Yanmar fuel pump leak

I am concerned about fuel in the crankcase. The oil level has been constant, which is reassuring. I keep thinking back to my days in the Navy, where we ran fuel oil dilution tests on a regular basis. But I don't have that equipment!

I am considering either ordering a new pump and installing it (but I hate throwing money at it), or finding a time when I can remove, inspect, replace, and then if needed order a new one (delivered to some place?) to do it all over again. Neither approach is appealing!
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Old 08-07-2021, 09:33   #4
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Re: Yanmar fuel pump leak

As someone who's also chased Yanmar (3GM30F) air leaks at sea the advice which I'd give is:
Renew ALL the Yanmar flexible hoses - I was getting leaks at the crimped connection points where those hoses joined to the banjo unions and said leaks varied in how serious they were depending upon the precise position of/twist in the hoses. That's what had me chasing for weeks, fit the hose one way and you got air-locked in twenty minutes, a fractionally different hose position and it was good for 6-8 hours, or until the exact moment that you entered confined waters, whichever came first. It sounds like you've already changed the hose up to the lift pump, but do you have other, shorter ones between the lift pump and secondary/fine filter housing and from that to the injection pump too? It's simple enough, carefully cut off those crimped hose couplings and you can fit a new hose to the existing banjo-bolts using s/s hose clamps/jubilee clips.
Secondly, when renewing all the copper sealing washers (you may already have done so?) rather than using copper replacements, if you can get them where you are, replace them with dowty washers instead, most especially on the two bleed screws atop the secondary filter housing and on the banjo union to the injection pump (no idea why that seemed more susceptible to leakage) but preferably dowtys everywhere; they also IMO make you less likely to strip and the threads on the pumps/filter housing.
Good luck.
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Old 08-07-2021, 11:09   #5
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Re: Yanmar fuel pump leak

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Originally Posted by sailingharry View Post
I am concerned about fuel in the crankcase. The oil level has been constant, which is reassuring. I keep thinking back to my days in the Navy, where we ran fuel oil dilution tests on a regular basis.
I am considering either ordering a new pump and installing it (but I hate throwing money at it), or finding a time when I can remove, inspect, replace, and then if needed order a new one (delivered to some place?) to do it all over again. Neither approach is appealing!
You say there is a fuel leak however. How much fuel are seeing? Something will need addressing. Just r/r it. There was a post recently about oil getting into fuel tank. Was a small hole/crack on diaphragm, just in the right place, oil was getting sucked in. I think u should change to pump. I don’t think it’s too “$” relative to other parts. Without eyes on it i can’t say where it’s coming thru, either the pump body or the seal. I’d change the oil too, after the pump(suspect) is replaced. It’ll be peace of mind. t I don’t want to start factoring x x amd x. But fuel, oil contamination, oil burn, oil level on dip. Can do funny things. Also diesel runaway.(pending pcv). I’m going on and on


Also. I’m replaceing fuel lines soon. And noted, all at once.
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