Fuel is drawn by the suction side of the fuel pump from the fuel tank into the ECU cooling plate and enters the fuel filter housing. Fuel passes by the one-way check valve which prevents the bleeding of fuel back to the fuel tank and into the primary fuel filter. The fuel becomes filtered by passing through the filter media from the outside to the center of the primary fuel filter. The fuel leaves the primary filter and passes by a one-way valve located in the threaded nipple of the primary filter. The fuel flows from the filter housing to the suction side of the fuel pump through an external fuel line.
Fuel becomes pressurized after leaving the fuel pump and flows back to the filter housing to enter the secondary filter. The fuel becomes filtered by passing through the filter media from the outside to the center of the secondary filter. The fuel leaves the secondary filter and passes by an automatic air bleed valve which is located in the threaded nipple for the secondary filter. Fuel passes by the fuel pressure sensor and then exits the filter housing to enter the rear of the cylinder head through an external fuel line. After fuel enters the cylinder head, it passes through the fuel gallery of the cylinder head to continuously deliver fuel to all six unit injectors.
Fuel leaves the cylinder head after passing by the fuel pressure regulator located at the left front corner of the cylinder head. Fuel is routed back from the cylinder head to the filter housing through an external fuel line to deliver some return fuel back into the suction side which goes to the fuel pump. Any excessive fuel not consumed is bled off through the de-aeration valve and then, directed back to the fuel tank. FUEL FILTRATION Primary and secondary filter elements attach to the underside of the filter valve housing. The housing, located at the front lower left side of the cylinder block, has an integral hand-priming pump for bleeding the system.
The 30 micron pre-filter (primary filter) also separates water from the fuel. Water collects in a cup on the bottom of the pre-filter. There is a sensor to keep track of the water and signal the EECU. A one-way check valve located in the filter housing prevents fuel from draining back to the fuel tank when the engine is shut down. Also included in the fuel filter housing is the fuel pressure sensor just above the secondary filter. The collected water can be dumped only while the engine is not running, the key is in the ON position and the parking brake is set. Some trucks are built with a remote mounted fuel water separator.
In this case, the fuel is drawn through the remote mounted filter before it reaches the ECU cooler plate. On the filter base, the mounting location for the standard primary filter is blocked off with a plate. Page 29 DESCRIPTION AND OPERATION