The Fuel System provides fuel pressure by an external fuel pump mounted under the vehicle near the fuel tank
outlet. The Powertrain Control Module (PCM) controls the operation of the fuel system by providing battery voltage
to the fuel pump through the fuel pump relay. The PCM requires only three inputs and a ground to operate the fuel
pump relay. The three inputs are:

•

Ignition Voltage

•

Crankshaft Position (CKP) Sensor

•

Camshaft Position (CMP) Sensor

The fuel pressure regulator and main fuel filter are combined into a single unit. A strainer inside the fuel tank also
provides a means of preliminary filtering of the fuel before it leaves the bottom of the fuel tank.

The fuel tank filler tube assembly, which is permanently fixed to the fuel tank, uses a pressure/vacuum 1/4 turn fuel
filler cap.

The evaporation control and Onboard Refueling Vapor Recovery (ORVR) systems should also be considered part of
the fuel system. They are designed to reduce the emission of the fuel vapors into the atmosphere. For complete
operation and function of these systems, refer to the Emission Controls section. (Refer to 25 - EMISSIONS CON-
TROL - OPERATION).

There are a total of four check-type valves within the fuel tank/fuel filler tube assembly. Two tank vent/rollover valves
(1) are inside and near the top of the fuel tank. They provide a means for vapors to vent, yet can close to prevent
fuel from entering the evaporative system in the event of a rollover. The fuel tank overfill check valve (5) uses a float
and closes the opening at the bottom of the fuel filler tube (3) as the level of the fuel reaches capacity to prevent
an overfill condition. The fuel filler tube check valve (4), located below the narrow portion of the tube, has a dual
purpose. It also prevents fuel from exiting the fuel tank through the fuel filler tube in the event of a rollover and
eliminates fuel from splashing back on the customer during refueling.

FUEL DELIVERY

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DIAGNOSIS AND TESTING - FUEL PRESSURE LEAK DOWN TEST

Use this test in conjunction with the Fuel Pump Pressure Test and the Fuel Pump Capacity Test.

CHECK VALVE OPERATION

The electric fuel pump outlet contains a one-way check valve to prevent fuel flow back into the tank, and to maintain
fuel supply line pressure (engine warm) when the pump is not operational. It also is used to keep the fuel supply
line full of gasoline when the pump is not operational. After 30 minutes the fuel pressure may drop to 2.5 bar (36
psi), but the liquid gasoline will remain in the fuel supply line between the check valve and fuel injectors. When the
fuel pump is activated, the fuel pressure should immediately (1-2 seconds) rise to specification.

Abnormally long periods of cranking to restart a hot engine that has been shut down for a shout period of time may
be caused by either fuel pressure bleeding past a fuel injector(s), or fuel pressure bleeding past the check valve in
the fuel pump. To determine the cause of this condition:

1. Remove the engine cover for access and disconnect the fuel inlet line at the fuel rail.

2. Connect the correct fuel line pressure test adapter tool between the disconnected fuel inlet line and fuel rail.

3. Connect Special Tool C-4799-B or equivalent to the test port on the test adapter tool.

4. Start the engine and bring to normal operating temperature.

5. Observe the test gauge. Normal operating pressure should be 3.7 - 4.1 bar (54 - 60 psi).

6. Shut engine off.

7. Pressure should not fall below 2.5 bar (36 psi) after 30 minutes.

8. If pressure falls below 2.5 bar (36 psi) within 30 minutes, it must be determined if a fuel injector, the check valve

within the fuel pump, or a fuel tube/line is leaking.

9. Again, start the engine. After bringing to normal operating temperature, shut engine off.

TESTING FOR FUEL INJECTOR OR FUEL RAIL LEAKAGE

Clamp off the rubber hose portion of the adaptor tool between the fuel rail and the test port “T”. If the pressure now
holds at or above 2.5 bar (36 psi) for 30 minutes, a fuel injector or the fuel rail is leaking.

TESTING FOR FUEL PUMP CHECK VALVE, FILTER/REGULATOR CHECK VALVE, OR FUEL
TUBE/LINE LEAKAGE

Clamp off the rubber hose portion of the adaptor tool between the vehicle fuel line and the test port “T”. If the
pressure now holds at or above 2.5 bar (36 psi) for 30 minutes, a leak may be found in the fuel tubes or lines or
one of the check valves. Note: A quick loss of pressure usually indicates a defective check valve in the pressure
regulator. A slow loss of pressure usually indicates a defective check valve in the fuel pump. These valves are not
serviced separately. If found defective, the entire component that the valve is a part of must be replaced as an
assembly.

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FUEL DELIVERY

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