Fuel Pump: Description and Operation

FEATURES
The fuel system has the following characteristics:
- It uses a high-pressure in fuel tank mounted electric fuel pump.

- The fuel pump is combined with a fuel level sensor.

- The vertical configuration fuel tank is constructed of sheet metal and incorporates an internal reservoir in which the fuel pump and fuel level sensor rest. This design enhances fuel pump operation during extreme vehicle maneuvers and on steep grades with low fuel levels.

- The high-pressure fuel pump supplies 60.0 L (15.9 gal) of fuel per hour at a working pressure of 269.0 kPa (39 psi).

- The fuel pump has an internal relief valve to provide overpressure protection if fuel flow becomes restricted (clogged fuel filter, damaged fuel tube, etc.).

- Overpressure is limited to 850 kPa (123 psi) and fuel flow will be reduced if pressure relief valve is actuated.

- The fuel pump is protected at its inlet by a nylon fuel filter element that filters dirt and other contaminants which could plug or damage internal fuel pump components. The fuel filter element also allows passages of small quantities of water, which may accumulate within the fuel tank reservoir.

COMPUTER CONTROLS
The electrical system has a fuel pump control relay controlled by the Powertrain Control Module (PCM) which provides power to the fuel pump through an inertia fuel shutoff switch which is normally closed.

The electrical system provides power to the fuel pump through two relays:
- fuel pump relay and powertrain control module relay.
- The power relays are located in the powertrain control relay module. The powertrain control relay module is serviced as a unit.

OPERATING CONDITIONS
Current path depends on operating conditions.
- Contacts of both relays are open when the ignition switch is in the OFF position.

- The powertrain control module power relay is energized, closing its contacts, when the ignition switch is first turned to the ON position.

- Power is provided to the fuel pump relay and to a timing device in the powertrain control module.

- The fuel pump runs through the contacts of the fuel pump relay.

- If the ignition switch is not turned to the START position, the timing device in the powertrain control module will open the ground Circuit 57 (after approximately one second).

- Opening the ground circuit de-energizes the fuel pump relay (opening its contacts) which, in turn, de-energizes the fuel pump. This circuitry provides for pre-pressurization of the fuel system.

- The powertrain control module operates the fuel pump relay when the ignition switch is turned to START position to provide fuel while cranking.

- After the engine starts and the ignition switch is returned to the ON position, power to the fuel pump is again supplied through the fuel pump relay.

- The powertrain control module senses engine speed and shuts off the fuel pump by opening the ground circuit to the fuel pump relay when the engine stops or is below 120 rpm.