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Fuel Pump Circuit Operation
When the ignition is switched to the ON position, it turns the EEC Power Relay on. The EEC Power Relay provides power to the EEC-IV processor and the control side of the fuel pump relay. Power for the fuel pump is supplied through a fuse link or high current fuse attached to the starter solenoid (battery side). From the fuse link or high current fuse, current flow is through the fuel pump relay and Inertia Fuel Shutoff (IFS) switch to the fuel pump. The IFS switch is a safety device used to shut off the fuel pump in the event of a collision. If the IFS switch is "tripped," it must be reset by depressing the white or red button on the top of the switch. The fuel pump relay is controlled by the Powertrain Control Module (PCM).
When the ignition switch is turned to the ON position, the fuel pump will operate. If the ignition switch is not turned to the START position, the PCM will shut the fuel pump off after approximately one second. The PCM will operate the fuel pump when the ignition is in the START position to provide fuel while cranking.
After the engine starts, the PCM will continue to operate the fuel pump unless the engine stops, engine speed drops below 120 rpm, or the IFS switch is "tripped."
Are Fuel Pump Relay socket contacts clean?
Test & Diagram at the Diagnostic Link Connector in 84-95; "...Connect FP Relay to any ground to force the fuel pump(s) on when the key is in RUN..." MIESK5 NOTE; from Ford EVTM; The Control Module (PCM) runs the pump{s} for one second when it receives an ignition- on signal. It also runs the pumps as long as it receives a PIP signal from the Hall-effect devices, it continues pump operation even after the key is released from START. If the PIP signals fall below 120RPM, the control module cuts off the signal to the fuel pump relay or the integrated relay control module. The pump will also run when the terminals of the fuel pump test connector are jumped. the Control module signals the pump when it receives a CRANK signal, and when the Control module gets PIP signals that the engine is running. the pump does not run if the PIP indicates the engine is not running even with ignition ON {except for that first one second}.
Source: by Steve
http://www.supermotors.net/registry/media/245234
Troubleshooting w/Wiring Diagram in 94-95 F Series; Miesk5 note that this is for F Series w/dual tanks & pumps; the R/Y wire from Inertia Switch to Fuel Pump is PK/BK on Broncos
Source: by seijirou at
Disconnect battery and check for continuity on LB/O wire from FP relay to PCM pin #22
EEC IV Connector Pin Diagram
http://web.archive.org/web/20131229163930/http://oldfuelinjection.com/images/eec04.gif
by Fireguy50 (Ryan M)
EEC Connector Pin Outs LEGEND, Bronco & Ford Truck & Van: 4.9, 460, 5.0, 5.8; by Ryan M (Fireguy50) at
http://web.archive.org/web/20131029020805/http://oldfuelinjection.com/truckpinouts.html
Connect Battery;
Test for batty power at FP relay DG/Y wire from relay to Splice
S139 Engine control sensor harness, near T/O to powertrain control module (PCM)