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 module is a combined assembly with a fuel gauge sender.

- The fuel pump module is mounted with its inlet at the bottom of the fuel tank reservoir. This design permits fuel pump module operation during extreme vehicle maneuvers and when fuel tank is nearly empty.

The high-pressure fuel pump is capable of supplying 80 L (21.0 gal) of fuel per hour at a working pressure of 269.0 kPa (39 psi).

The fuel pump module:
- has an internal relief valve to protect the fuel pump module from overpressurizing if the fuel flow becomes restricted (for example, clogged fuel filter and base or damaged fuel tube). Overpressure is limited to 850 kPa (123 psi) and reduced fuel flow will result.

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


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 module through an Inertia Fuel Shutoff (IFS) switch, which is normally closed.
- provides power to the fuel pump module using PCM relay and a fuel pump power relay.

OPERATING CONDITIONS
The current path is dependent upon the operating conditions.

When the ignition switch is in the OFF position the contacts of both relays are open.

When the ignition switch is first turned to the RUN position:
- the PCM power relay is energized, closing its contacts.
- power is provided to both the fuel pump relay and to a timing device in the PCM relay.
- the fuel pump module is powered through the contacts of the fuel pump powertrain control module relay.

If the ignition switch is not turned to the START position, the timing device in the PCM relay will open the ground Circuit 57 (after approximately one second). Opening the ground circuit de-energizes the fuel pump powertrain control module relay, opening its contacts, which in turn de-energizes the fuel pump module. This circuitry provides for pre-pressurization of the fuel system.

When the ignition switch is turned to the START position, the PCM power relay operates the fuel pump relay 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 powertrain control module relay.
- the PCM relay senses engine speed and shuts off the fuel pump by opening the ground circuit to the fuel pump relay when the engine is below 120 rpm or the engine stops.