NOTE: Early fuel filter assemblies may have item 2 in the location of item 9. Item 2 is used by the assembly
plants as a fuel fill.
• If item 2 is installed on housing cover assembly, it can be used to measure unfiltered fuel pressure.
• If item 2 is installed in item 9 location, it can be used to measure fuel inlet restriction.
The low-pressure fuel supply pump draws fuel from the fuel tank through a 150 micron strainer in the fuel filter assembly.
An optional electric heating element in the fuel filter housing warms incoming fuel to prevent waxing.
If water is in the fuel, the filter element repels water molecules, water collects at the bottom of the element
cavity in the fuel filter housing, and a Water In Fuel (WIF) sensor in the element cavity detects water in the fuel. When enough water accumulates in the element cavity, the WIF sensor signal changes to the
Electronic Control Module (ECM). The ECM sends a message to illuminate the amber water and fuel lamp,
alerting the operator. A fuel drain valve handle on the housing can be opened to drain contaminants (usually
water) from the fuel filter housing. Another drain valve in the bottom of the housing drains strainer cavity.
A built-in fuel regulator valve, calibrated to open at about 414 – 482 kPa (60 – 70 psi), regulates and
relieves excessive pressure. During idle and light engine loads, when injector demand is low, most of
the fuel is recycled between the fuel filter housing and fuel pump. When engine demand increases, engine fuel consumption increases resulting in less fuel recycling. Under heavy loads fuel flows through the filter with little or no recycling.
Fuel is conditioned as it flows through a main filter and stand-pipe. The stand-pipe prevents fuel from draining from the fuel rail during servicing.
An optional Engine Fuel Pressure (EFP) sensor detects low pressure caused by high fuel filter restriction and sends a signal to the ECM. The ECM illuminates the amber FUEL FILTER lamp on the instrument panel.
Fuel flows from the fuel filter housing into the fuel rail, through the fuel rail into six separate passages, one for each injector.
When the fuel injectors are activated, fuel flows (from fuel rail) into four inlets in each injector.
