sb8 fuel system

ALNims · Jun 3, 2015

trapoc said:
Hi
I'm getting a little air from my injection pump that air locks the system after running for about ten minutes . I have eliminated all other parts of the fuel system and still get the air. I have removed the injection pump and injector. I have disassembled both parts and inspected and visually no wear. I can keep the engine running if i continually bleed the high pressure side. Any thoughts on this?

You are sucking in air somewhere. Have you recently done any maintenance on the fuel system? Was the fuel system operating okay before the maintenance? Do you have any leaks on the suction side of the fuel pump in the fuel system suction piping or fittings with the engine shut down? Have you attempted to tighten all connections in the fuel system? If you have done any filter maintenance I would make sure I replaced any o-rings. Please keep us posted on your results. These are just a few possibilities.

kloudie1 · Jun 4, 2015

Trapoc.. concentrate on the line from the fuel pickup to the lift pump.. Carefully look over that line and its connections..The problem is most likely a tiny air leak in the section of the line (or any fittings, including the suction side banjo washers/connectors) that is between the tip inside the tank and the lift pump.. The line can sometimes leak air without leaking liquid fuel..

ALNims · Jun 5, 2015

trapoc said:
Kloudie1 i am not getting any air from the lift pump to the high pressure pump. I replaced the base gasket below the high pressure pump and still have a very small bit of air coming out of the high pressure pump. I checked the spray pattern of the injector, it is a perfect circle when sprayed at a piece of paper. It also is a fine mist. The engine wont start anymore and only occasionally sounds like it wants to start. I did a valve job and head mill 5months ago. It cranks like it has great compression. I am going to give it a shot of starting fluid tomorrow to see if it start. I think its fuel starved.

I would like to suggest that you hire a certified engine mechanic. You may have high pressure pump problem. You are in over your head and your engine is getting worse not better. The possibility of you damaging your engine seriously and this point is very high. You could easily spend far more money than you originally need if you continue your DIY effort.

ALNims · Jun 5, 2015

trapoc said:
Al Nims would you like to cover that certified mechanics bill for me? Al you never asked me what profession I'm in or how long i ha e been in that profession.

Your absolutely right about who covers the bill. However I do know that that the high pressure fuel pump provides metered fuel to the injectors based on demand. I also know on starting the engine that the fuel rack goes to full and then backs off once you reach idle speed. I also know that that rack positions the high pressure fuel pump. If you have changed the base gasket on the high pressure fuel as you have stated earlier, then there is a high probability that you have not reassembled it properly which is why your engine won't start. This indicates that you need a certified mechanics assistance or you wouldn't need to ask this forum. Are you a certified diesel mechanic? I am USCG Licensed Chief Engineer Steam, Motor and Gas turbine of any Horsepower. That means that I am certified to work on the largest ships out on the ocean commercially. I have 42 years experience at sea. Even though I will admit I don't know everything, I also know that it is possible at times, that I may need assistance with a piece of equipment that I may not be fully familiar with. Based on what I am seeing you go through I would strongly urge you to consider seeking professional technical help before you find yourself paying a large bill that you will regret later. Your boat, your call. Best of luck.

kloudie1 · Jun 6, 2015

Still sounds like air coming into the system before the lift pump.. When the engine idles, the pump is pulsing 7-8 times a second.. a very tiny air leak on that side will accumulate in a high spot (flow velocity isn't high enough to pass the bubble along) and shut the motor off.. Bleeding by hand pumping might not pull in enough air to notice compared to the rapid pumping of running. A multi cylinder is easier because ya have more velocity.. If you are getting air into the HP pump, it almost has to be coming from the suction side of the lift pump.. even something like a little split in the pickup tube inside the tank or a bad valve packing on the cutoff valve at the tank.. It is possible to have air suck into the HP pump when the engine is shut off but you would have to have bad valves in the lift pump and or a leak in a line that would leak diesel while the engine is running.. Happy hunting..
I am not a professional diesel mechanic but I did sleep in a Holiday Inn Express once!

Charles Erwin · Jun 6, 2015

Possible fracture in the pickup (dip) tube - inside the fuel tank. If you have not done so try a completely separate fuel can above the motor, make up a hose line from that fuel can to the lift pump or your separate electric bypass lift pump.

Or remove/inspect/test dip tube and its shut off valve.

Charles

ps one more thing - no starter fluid else you will pound the top ring land to death.