Installation manual

90-898305

4-14

Basic Fuel System Description

Fuel for the engine is stored in a typical fuel tank. A primer bulb is installed

into the fuel line to allow priming of the fuel system. A crankcase mounted

pulse driven diaphragm fuel pump draws fuel through the fuel line, primer

bulb, fuel pump assembly and then pushes the fuel thru a water separating

fuel filter. This filter removes any contaminates and water before the fuel

reaches the vapor separator. Fuel vapors are bled into the air compressor

inlet in the front of the flywheel cover preventing a vapor lock of the electric

fuel pump assembly which is mounted in the vapor separator. The electric fuel

pump is different than the fuel pump that is utilized on the standard EFI engine

(non DFI), and is capable of developing fuel pressures in excess of 90 psi.

Fuel inside the rail must remain pressurized at exactly 10 psi over the air rail

pressure or the ECM (map) calibrations will be incorrect. Fuel from the vapor

separator is supplied to the top of one fuel rail. A fuel line connects the bottom

of the first rail to the opposite fuel rail. Fuel is stored inside the rail until an

injector opens. A fuel pressure regulator controls pressure in the fuel rails, and

allows excess fuel to return into the vapor separator. The fuel regulator not

only regulates fuel pressure but also regulates it at approximately 10 p.s.i.

higher than whatever the air rail pressure is. The fuel regulator diaphragm is

held closed with a spring that requires 10 p.s.i. to force the diaphragm off the

diaphragm seat. The back side of the diaphragm is exposed to air rail

pressure. As the air rail pressure increases, the fuel pressure needed to open

the regulator will equally increase. Example: If there is 50 p.s.i. of air pressure

on the air rail side of the diaphragm, 60 p.s.i. of fuel pressure will be required

to open the regulator. The return fuel line to the vapor separator is water

cooled. This design is used to prevent cold fuel from the fuel tank hitting the

hot fuel returning from the fuel rail and flashing off the light ends (boiling over).

To equalize the pulses developed by the pumps (both air and fuel) a tracker

diaphragm is installed in the starboard rail. The tracker diaphragm is

positioned between the fuel and air passages. The tracker diaphragm is a

rubber diaphragm which expands and retracts depending upon which side of

the diaphragm senses the pressure increase (pulse).

Notes

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