air in fuel line

[T Dugas]

I changed the filters on my yanmar 27hp diesel, once changed with new gaskets installed I refilled the filter cups with fuel and tightened them. I bled out all air and everything appeared fine. After running the engine for approx. 30 minutes I had power loss and the engine quit. Bled off air that I thougt was the cause and it was and it happened a couple more times on the trip.I removed the filters again in port, installed new gaskets once again bled the system off. Again appeared alright thou tough to tell except by engine smoothness and RPM's since it has no fuel pressure guage. But low and behold it still has a small amount of air intrusion which causes a slight loss of power and it stalled last trip. Always corrects with air bleed off. Before I remove some hosing and perform a pressure check on the lines was wondering if this has happened to you and how you corrected it.

 

[Steve Dion]

Maybe you have a bad hose or fitting?

Sounds like everything should be OKAY. I assume that you have bled both of the bolts (with the phillips blade in them). Did you mess with the secondary filter on the engine? If you did you may want to loosen this up again and reseat.The next thing to check is the banjo washers (cannot reuse) they must be replaced. Clean up the engine and wipe down, then you can sprinkle a little talc powder and see if you have a leak. Very difficult to see fuel leak with good clean fuel and a clean engine. Also check your hose fittings from the tank to the filter and filter to the engine. They could be a little loose and you'd never notice it.

 

[Mike McKendy]

Been there, done that

I've just gone through several weeks of something the same. Steve's suggestions are spot on. I had air entering and ended up stripping the bleed screw on the secondary filter. Got that fixed and still had air. After several tries I fixed the problem. To emphasize Steve's point, the copper washers on the banjo fittings can really only be tightened once. They are soft and can easily be overtightened or flattened to the point where they don't seal.Also, depending on what type of primary filter you have, there could be problems here. I have a racor where the filter drops into a cannister which threads onto the top. There is a rubber gasket which can kink or otherwise not seal properly - check this carefully.After I had done all of this, I still had RPM slowdown and power loss. I got grunge at the end of the pick up tube in the tank. There may be a screen there and conventional wisdom goes that it should be removed.It may be a somewhat arduous process (as it was for me) but if you keep at it you'll track it down and it'll be a great way to get intimate with your fuel system,Good luck,Mike

 

[John Tesoriero]

Air in fuel system

The repair manuals say that air can be sucked into a fuel system anywhere between the tank and the fuel pump (suction side of the system). Beyond the pump, there is pressure in the fuel system and you will get a fuel leak rather than more air entering.

 

[John Tesoriero]

Air in fuel system

The repair manuals say that air can be sucked into a fuel system anywhere between the tank and the fuel pump (suction side of the system). Beyond the pump, there is pressure in the fuel system and you will get a fuel leak rather than more air entering.