Hoping for some help form Yanmar
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.....?