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HPDI 2 STROKE Fuel System Theory of Operation

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  • HPDI 2 STROKE Fuel System Theory of Operation

    From the motor you have an onboard filter with water sensor located on the port side. It’s a paper filter in a clear glass bowl.

    You have a couple of low pressure fuel pumps with diaphragms that do nothing but pulls the fuel from the Boats fuel tanks and fills the VST tank. They get leaks and should be replaced every few years. They cause poor running especially at idle. The use the engine vacuum pulses to pump fuel.
    Next you have a float in the VST(Vapor Separator Tank). That float blocks of the inflow of low pressure fuel when the tank is full.

    The VST tank is common in most fuel injected systems as the electric pump can't pump vapor (vapor lock). The fuel vapor is vented off the top and the liquid fuel is about 2-3" or so deep.
    The electric fuel pump sits in there with a VST 10 MICRON Filter/Screen on the bottom of it so it doesn't suck crap up. That pump is cooled by the fuel actually flowing through it and it shouldn't be allowed to be empty. That pumps puts out somewhere in the neighborhood of 55lbs PSI and should maintain it while the engine is running under a load. It has a shraeder valve on top to measure the pressure.

    Next that goes through a mid pressure filter (A 10 MICRON Filter) before it reaches the High Pressure Pump.

    Next that 55PSI fuel goes to the high pressure belt driven pump which pumps it up to north of 700PSI and pressurizes the fuel rails on each bank of cylinders. The "mystery filters" ( Four; 3 MICRON MICRO Basket Screens) are in that pump outlet and one 3 MICRON MICRO Basket Screen in the head of each injector (6 ea).

    Lastly you have injectors on the fuel rail that open once the piston is up part way so that the fuel is sprayed at a high pressure into a compressed air cylinder while the exhaust ports are covered. That's the HPDI part; it operates more like a diesel injecting fuel verses a 4 stroke fuel injection. Lastly a spark plug fires.

    Ball valves, fuel line and such are tank/line issues and unrelated to the motor. They are also cheap. In each boat fuel tank is a fuel pickup tube. Each will have a screen and an ant-siphon valve barb on each. These will sometimes clog up or stick closed, etc. In my Basscat I have an additional fuel water separator filter (A 10 MICRON FILTER) that the fuel goes through before it gets to the Engines fuel filter on the port side of the engine.

    the VST...

    Last edited by just1more; 11-02-2012, 07:21 AM.
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