Yanmar 2gm20f air in fuel problems

[SSAsailor]

Hoping for some help form Yanmar GM folks.....
Boat is new to me last June (2015). Have had engine die from air in fuel a few times - engine restarts fine after going through complete fuel bleed procedure. First time it happened was just 24 hours after purchasing boat. In each case, I was able to restart without much trouble if I bled but problem has always come back. The engine started and ran fine (for at least 1 hour) after careful bleed procedure. Evidence suggest that engine can avoid problems if run gently (~2200 rpm or below), but has run for up to 3-4 hours before having problems. This time, I was pushing the motor at 3000 rpm to test and that seems to have helped push issue.

Each time I have checked primary fuel filter and fuel is not dirty or green with bugs - no sign of water. I have probed the bottom of the tank and have not found any water or significant amount of sediment. So I don't think the fuel is the problem. I replaced all rubber fuel hoses and associated clamps this past winter to cross that off as problem, but problem has persisted. This time, I checked the fuel tank vent and ended up replacing the deck-end fitting - but I found no blockage so I don't think that's the problem.

I cannot see any air bubbles forming in the primary fuel filter (it has clear bowl). I read in Calder's diesel book that I should try disconnecting the outlet from the lift pump and pumping into a jar of diesel to check for bubbles, but the pipe is solid so I can't practically do that.

I have two ideas for what to try next, but don't think either seems like a slam-dunk, so I'm hoping for help.
One is that somehow the primary fuel filter is allowing air in, but I have no idea how. The filter unit seems fine, I have replaced the element multiple times and the gaskets seem to be well seated. It is a racor 120 unit (I am using 30 micron elements)
The other is that something could be wrong with lift pump and it is not pumping enough fuel to supply the injection pump at moderate to high throttle, and the deficit is drawing in air. I have read how to take the lift pump apart and test (pump in a pool of kerosene to check for bubbles), but it is hard to access and disassemble on my installation so I don't want to do this until its the most likely problem. Its hard to believe that it is faulty because it has no problem pushing out bubbles when bleeding system.

What to do next.....?

[lockie]

Have you replaced the copper washers on the banjo bolts? They can work-harden enough to make a tiny leak that lets air in (has happened to me).

Does your bleeding procedure include the bleed screw next to the injector pump inlet? It is not mentioned in the procedure as described in my Yanmar manual, but sometimes needs to be done.

Other than that, it seems the lift pump might be the next thing to rule out.


Sounds like a right pain, good luck with it.
Graeme

[Schrewsburyduo]

could also be a tiny crack in the casing for the engine fuel filter. or a crack in the fuel hose. I had a totally similar problem when I purchased my boat - I also have a g2m20f. I ended up replacing everything south of the engine - new racor (the boat came with some prehistoric looking filters), new fuel line from the motor to the racor and to the tank. emptied tank. new fuel. added stanadyne. never had a problem since.

[hugosalt]

Had similar problem years ago with my 3GM, but my problem was only when boat heeled
(on either tac) otherwise would run all day. But trouble shooting is same. You have done some good work already. Basiclly you want to isolate as much as possible to eliminate/pinpoint problem. First suggest you buy a small portable 2-3 gallon tank, (I ran
off this day tank set up for more than a year while trouble shooting).
As you can by pass, one by one, your main fuel tank, Racor filter, secondary filter while using small day tank.
Once before day tank set up, to get home cut the bottom out of a
plastic coke bottle duct taped it to stern rail and ran fuel line direct to motor.
Also, if you haven't already been doing, buy some copper crush washers to change for when you bleed motor.
How old is your boat? Have heard of air infiltrating at pick up tube/fitting.
After I tried to resolve, had 2 very confident mechanics try with no luck, I resolved
by going thru/changing all second time. Still have spares including fuel pump.

[hugosalt]

Thinking there are some good threads with extensive discussion on this subject on forum if you do a search.
And welcome to CF.

[SSAsailor]

I had not considered the copper crush washers. I have replaced a few of them in turn when fuel lines were apart, but never suspected the rest.

The secondary filter on the engine is new - I had to replace that last year when I over torqued the bleed screw and it wouldn't close. I understand this is a common mistake!

I am well aware that proper bleeding on this motor always includes the bleed screw on the injector pump inlet. Learned that after the first shut down.

I hate to have to just replace the rest of the stuff between tank and engine - I'm hoping to find some tips on how I can find the problem besides replacement. Anybody have any lift pump troubleshooting tips before pulling it off the motor? Motor is a 1986 2gm20f - so yes, most parts not already replaced are assumed to be old (that is part of the reason I started with replacing hoses)

I'm remembering now that I had some new info from my outing the other day. When I try to run at anything over 2200-2400 rpm or so, whether in neutral or in gear, the engine won't maintain revs unless I hold the throttle. I tried adjusting the throttle lever directly on the engine and no difference in behavior so I don't think this is a throttle cable issue. Seems like this could be a related issues, perhaps not enough fuel getting to the engine to maintain revs?

[hugosalt]

[QUOTE=SSAsailor;2121364]

I hate to have to just replace the rest of the stuff between tank and engine - I'm hoping to find some tips on how I can find the problem besides replacement.


That is why you want to start with by passing/eliminating/isolating the problem.
When, after systematically troubleshooting, problem was not clearly evident in my case, I choose to replace parts. Hopefully you will find issue not have go that route.

Your 1986 probably has a screen in the lower part of your pick up tube in your tank. Could be partially clogged. If it has not been removed, it should be removed.

[Sea Painter]

I had this very same problem on my 2QM15 and had went through all of the common test and evaluations. Replaced all lines, clamps, filters, and all crush washers. Every time after running for a bit, it would starve for fuel, and wouldn't restart until bleeding the lines. Solution: this engine did not have a fuel return line to the tank. Added return line, problem solved. Hope this helps.

[boeing1]

how old is the boat, if it is a older boat yes recheck fuel lines, and a good point on the crush washers on the banjo fittings, if as you say filters are clean might check the pickup from your tank

[Philsboat]

Originally Posted by SSAsailor

Hoping for some help form Yanmar GM folks.....
Boat is new to me last June (2015). Have had engine die from air in fuel a few times - engine restarts fine after going through complete fuel bleed procedure. First time it happened was just 24 hours after purchasing boat. In each case, I was able to restart without much trouble if I bled but problem has always come back. The engine started and ran fine (for at least 1 hour) after careful bleed procedure. Evidence suggest that engine can avoid problems if run gently (~2200 rpm or below), but has run for up to 3-4 hours before having problems. This time, I was pushing the motor at 3000 rpm to test and that seems to have helped push issue.

Each time I have checked primary fuel filter and fuel is not dirty or green with bugs - no sign of water. I have probed the bottom of the tank and have not found any water or significant amount of sediment. So I don't think the fuel is the problem. I replaced all rubber fuel hoses and associated clamps this past winter to cross that off as problem, but problem has persisted. This time, I checked the fuel tank vent and ended up replacing the deck-end fitting - but I found no blockage so I don't think that's the problem.

I cannot see any air bubbles forming in the primary fuel filter (it has clear bowl). I read in Calder's diesel book that I should try disconnecting the outlet from the lift pump and pumping into a jar of diesel to check for bubbles, but the pipe is solid so I can't practically do that.

I have two ideas for what to try next, but don't think either seems like a slam-dunk, so I'm hoping for help.
One is that somehow the primary fuel filter is allowing air in, but I have no idea how. The filter unit seems fine, I have replaced the element multiple times and the gaskets seem to be well seated. It is a racor 120 unit (I am using 30 micron elements)
The other is that something could be wrong with lift pump and it is not pumping enough fuel to supply the injection pump at moderate to high throttle, and the deficit is drawing in air. I have read how to take the lift pump apart and test (pump in a pool of kerosene to check for bubbles), but it is hard to access and disassemble on my installation so I don't want to do this until its the most likely problem. Its hard to believe that it is faulty because it has no problem pushing out bubbles when bleeding system.

What to do next.....?

I had the same problem with 1GM10.Found a loose fitting on the suction side at the tank.Check all the connections from the tank to the pump.

Phil

[SSAsailor]

hugosalt - good idea to check tank
The pickup appears to be threaded into the top of the tank, but it doesn't turn - I haven't pushed it very hard because I don't want to break it - unless I'm ready to replace whatever it is attached to, in this case the whole tank. Any advice on what I should do to remove this thing? See link to image, valve in foreground is pickup with hose barb unscrewed...

[Scaramanga F25]

I had similar problem. Hairline crack on bottom of metal pipe between secondary filter and high pressure pump.
Worked fine at low RPM and fuel starved at higher RPM.

[a64pilot]

It's screwed in, worse case you wring it off, then it will have to be drilled out and re-tapped. West Marine and I'm sure others too sell a replacement where the dip tube is plastic and you cut to length.
I home made one for a short while that was a copper tube soldered into a brass fitting, but concern over copper being in an aluminum tank made me find the WM already made one.
Seeing how buggered up it looks, is it possible that is where your air leak is coming from?
But, eventually you will have to be able to remove it in my opinion, eventually it will clog with something, so bite the bullet now while you have the time and repair facilities to fix it

[a64pilot]

Heat gun and slowly turn one way then the other til it gets loose is what I would try.
I doubt penetrating oil would do any good as it's likely a pipe thread, but it wouldn't hurt either

[MikePz]

Or your exhaust elbow is beginning to clog with soot which does not let you increase RPMs, doesn't solve the air intrusion!