Thunderbird V8-4.6L VIN W (1997)
Fuel Pump Relay: Description and Operation
System Operation
Description
The electrical system provides power to the fuel pump through two relays: fuel pump and powertrain control module relays, which provide power to the
fuel pump through a normally closed Inertia Fuel Shutoff switch (IFS). The power relays are located in the powertrain control relay module, which is
serviced as a unit.
Operation
Current path depends on operating conditions:
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Contacts of both relays are open when the ignition switch is in the OFF position.
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The powertrain control module power relay is energized, closing its contacts, when the ignition switch is first turned to the ON position.
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Power is provided to the fuel pump relay and to a timing device in the powertrain control module.
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The fuel pump runs through the contacts of the fuel pump relay.
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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).
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Opening the ground circuit de-energizes the fuel pump relay (opening its contacts) which, in turn, deenergizes the fuel pump. This circuitry
provides for prepressurization of the fuel system.
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The powertrain control module operates the fuel pump relay when the ignition switch is turned to START position to provide fuel while cranking.
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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.
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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.
