This should be easy, but, it has been driving me nuts......engine runs perfectly as long as there is fuel pressure. Stop the engine for more than a few minutes and it requires bleeding. Have two tanks and two separate filtering systems. Problem occurs on either system. Any suggestions? jerry
Yanmar 2gm20-air infiltration
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You most probably have a leak in the fuel delivery system: loose/leaky 'compression' fitting somewhere in the (copper) tubing, developing pin hole in the tubing (corroded?), bad gasket, etc. on one of your fuel filters, pin hole in the lift pump diaphragm. .... and possibly a 'restriction' developing in the fuel lines that is causing the high vacuum: blocked tank atmospheric vent, clogged fuel filter(s), clogged 'screen' on the dip tube in the fuel tank(s).
Suggest the following: Start with the very 'last' item/area that you 'maintained' and look for the errant 'leaker', then if not found apply a vacuum gage to the 'secondary filter' then close the valve at the fuel tank then close to develop vacuum and shut down the engine ... if the vacuum gage reading then slowly 'drops' there IS a leak between the injection pump and the tank valve ... and you will HAVE to find it. Tighten all 'compression fittings' as they are notorious 'leakers', then change the filters, inspect the entry to the 'diptube', then inspect the lift pump diaphragm for a developing pin hole, etc.
hope this helps.
Suggest the following: Start with the very 'last' item/area that you 'maintained' and look for the errant 'leaker', then if not found apply a vacuum gage to the 'secondary filter' then close the valve at the fuel tank then close to develop vacuum and shut down the engine ... if the vacuum gage reading then slowly 'drops' there IS a leak between the injection pump and the tank valve ... and you will HAVE to find it. Tighten all 'compression fittings' as they are notorious 'leakers', then change the filters, inspect the entry to the 'diptube', then inspect the lift pump diaphragm for a developing pin hole, etc.
hope this helps.
Let me suggest
All the items listed are possibilities, and could take some time to check all of them. The very first thing I would look at is the fuel return line. It runs from the rear of the injector rail, and is routed to different places on Yanmars. Re route the return line, directly back to the tank if it is not routed that way. I ran mine back and T ed it into the fuel vent hose, right above the tank. If it is not the problem now, it will be at some time in the future. It would seem that you have a pretty good leak somewhere, and if it's not the return line, I would install an electric pump at the tank and look for drips with pressure on the system. The electric pump also can make bleeding a pleasure compared to the manual lift pump. I had a similar problem last year, and found that the PO had made a splice using PVC connections, back in behind the sink. Good luck.
All the items listed are possibilities, and could take some time to check all of them. The very first thing I would look at is the fuel return line. It runs from the rear of the injector rail, and is routed to different places on Yanmars. Re route the return line, directly back to the tank if it is not routed that way. I ran mine back and T ed it into the fuel vent hose, right above the tank. If it is not the problem now, it will be at some time in the future. It would seem that you have a pretty good leak somewhere, and if it's not the return line, I would install an electric pump at the tank and look for drips with pressure on the system. The electric pump also can make bleeding a pleasure compared to the manual lift pump. I had a similar problem last year, and found that the PO had made a splice using PVC connections, back in behind the sink. Good luck.
Thanks, all (except for Ken in Singapore, who is either very rich, or a nitwit, or both). I ran into this problem years ago and solved it with a new lift pump. I inspected my lift pump and changed it before I came on here. The gasket was no longer supple, even though I could not see an obvious breach. Same problem, but, now I have an emergency spare.
My secondary pump is practically empty when the engine is off for a while. Can this be caused by anything downstream of the filter (oh, no, not the injection pump!), or does the breach have to be upstream? jerry
My secondary pump is practically empty when the engine is off for a while. Can this be caused by anything downstream of the filter (oh, no, not the injection pump!), or does the breach have to be upstream? jerry
Ahhh Grasshopper ! The ways of the banjo connection are perverse indeed!
One would think that the check valves in the lift pump would make everything downstream of it a non suspect but not so.. Nice & Easy had a very similar one and his modification fixed it. You don't mention what year the engine is.. Some Yanmars (newer) have the secondary filter as the highest point on the fuel system, the best suspect .. in any case the return line can syphon everything from the outlet of the lift pump back to the tank .. Jerry, it really doesn't sound like anything more than an air leak and is most likely not an injection pump problem.. There are some new banjo washers made with a neoprene covering.. The Yanmar guy didn't offer them until I asked.. I have some now on my lift pump banjos.. but they've only been on for a couple of weeks.. way too early to say they are better. I have had the inlet banjo to the lift pump come loose a couple of times and it did exactly your problem.. The inlet fuel line on mine is close to the raw water filter and if I bump the line, it loosens the banjo just enough to leak air in but still allows enough fuel flow while running .. It doesn't leak diesel when that is going on ! Perverse, I tell ya.
One would think that the check valves in the lift pump would make everything downstream of it a non suspect but not so.. Nice & Easy had a very similar one and his modification fixed it. You don't mention what year the engine is.. Some Yanmars (newer) have the secondary filter as the highest point on the fuel system, the best suspect .. in any case the return line can syphon everything from the outlet of the lift pump back to the tank .. Jerry, it really doesn't sound like anything more than an air leak and is most likely not an injection pump problem.. There are some new banjo washers made with a neoprene covering.. The Yanmar guy didn't offer them until I asked.. I have some now on my lift pump banjos.. but they've only been on for a couple of weeks.. way too early to say they are better. I have had the inlet banjo to the lift pump come loose a couple of times and it did exactly your problem.. The inlet fuel line on mine is close to the raw water filter and if I bump the line, it loosens the banjo just enough to leak air in but still allows enough fuel flow while running .. It doesn't leak diesel when that is going on ! Perverse, I tell ya.
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