Engine Slowdown question

Yes that check valve is a non return valve to prevent fuel leaking when the fuel lift pump isn't providing suction. I removed mine years ago with all sorts of gunk in there.... I installed a standard bronze shut off valve from the hardware store to meet the ABYC code and never had a problem since. However one engine I worked on managed to get lots of junk into the filter that is in the fuel lift pump and until that was cleaned the engine would do the same and just slow down to an idle... So blockage points start at the fuel feed nipple and then the fuel lift pump, then the bukh spin on fuel filter.... and of course any fuel filter in between all that.

Interestingly even an air leak on the fuel system can have the same symptom. So one has to be sure they see no fuel leaks as this would likely indicate a possible air leak in the fuel system.

The stock check valve is a ball bearing with spring mounted inside the fuel tank "fuel feed" hose nipple.... the spring actually catches all the junk and it can't get past the ball bearing causing a blockage. Just unscrew the nipple, put it on an anvil and use a small flat punch and the ball bearing and spring will pop right out. Suction from the fuel lift pump causes the ball bearing to compress the spring and allow fuel to flow thru.... anyways it came on all the L28 fuel tanks.


Edited by Bill Layton - 12 September 2014 at 4:57pm

From Chris Winn comes the good suggestion that one might also look into the fuel tank vent system. Sometimes small spiders or other insects build nests in those vents and totally block it. Then, a vacuum would set up. The Bukh uses very little fuel per hour, so one might think this impossible, but those little vents can certainly be plugged by insects. It's an easy check. Just disconnect at tank and blow through.

I can find longer filters but they hit the high pressure pipe and start leaking. So the bukh filter seems the only solution

I suspect sediment somewhere.  If it ran for an hour and slowed down, that may have been the point where sediment accumulated enough in one of the filters Frank describes above to cause an engine slowdown.  After shutting off, perhaps the sediment settled a bit, allowing you to restart for the quick motor into the slip.

I could suggest trying varying combinations of engine starts and running for periods of time to try and establish a pattern, but the time spent doing this could just as easily be spent inspecting and replacing the fuel filters.  I have a small inline filter I purchased at an auto parts store between the tank and the fuel lift pump, which is transparent and easy to inspect.  Next is the Bukh engine fuel filter as the secondary. 

If you have an inline filter that is easy to inspect, start there.  If no debris present, move back to the fuel tank.  Inspect and if debris found, I would use a brush to try and stir up as much sediment as possible then use an evacuator pump with a large bore hose to remove the diesel while the debris is still in suspension.  Add clean diesel and repeat.  Then add clean diesel and diesel conditioner with anti-microbial properties (I use this all year, not just for winterizing although I understand this is a debatable topic).

If debris is present in the primary filter, you need to move along to the Bukh filter as this may be contaminated too.  Then repeat everything above for the tank.

Hose replacement would be optional, but hoses are cheap so why not?

If that doesn't solve the problem, turn your attention to the injector nozzles but if the filters were doing their job properly, the injector should be fine.

Not sure I understand the fuel line thing. The fuel is usually filtered twice. Once coming off the tank before going to the high lift fuel pump, and then again before it enters the high pressure injector pump via the screw on canister-type filter. Obviously those must be clean enough to pass fuel.

Next would be to check contamination in the bottom of the tank. It can be hard to see, but the bottom of the tank could be full of sludge from mold growing in the fuel over several winters etc. The tank is the source of the fuel so must be clean. There is a small screen on the bottom of the fuel pick-up at the bottom of the tank. It must not be full of sludge.

Lets assume that both fuel pumps are good, then the next thing would be the injector nozzle on top of the head. This thing atomizes the fuel into the combustion chamber via 4 or 5 tiny holes each 9/1000". If any sludge or debris got through your filters, these things can plug. Do not try cleaning them without the correct diameter spring wire for doing so….not that easy to find. Do not try using a needle or something like that because you will deform the hole, or break the point off in the hole. How do I know that? :-(

The above are likely the problem. The only other thing is a compromised fuel line on the suction side causing a break in the vacuum that lifts the pump from the tank. This can be a cracked fuel line or a loose or compromised fuel fitting leading to the high lift pump. If all the above are satisfied, you should have power.