Fuel Pressure: Testing and Inspection

The following tests can be used to determine if the fuel pump is operating properly.

Fig. 14 Fuel pump relay modification:

1985 Continental & Mark VII; 1985---87 Cougar & Thunderbird; 1986 Capri & Mustang

1. Check for adequate fuel supply.
2. Check for fuel leakage at all lines and fittings.
3. Check for electrical continuity to fuel pump as follows:
a. Locate 14 gauge (pink/black) fuel pump power feed wire at grommet in trunk or at fuel pump relay and connect a suitable volt-ohmmeter between that point and ground.
b. Measure resistance to ground with ignition key in the Off position.
c. If resistance measures 5 ohms or less, proceed to step 3d. If resistance measures more than 5 ohms, check for continuity of the pump ground circuit. If satisfactory, check body ground or wiring between fuel pump and body ground. If resistance is still more than 5 ohms, remove fuel tank and check for poorly mated fuel pump electrical connection or faulty pump. Measure resistance across fuel pump terminals. If resistance is within limits, check wiring and repair as needed. if resistance is not within limits, replace fuel pump and proceed to step 3d.
d. Set meter to indicate voltage, then turn ignition switch to the On position. Voltage should rise to 10 volts or more for one second, then return to zero. If voltage reading is not as specified, inspect wiring and repair as necessary.
e. Ensure inertia switch is set by depressing white button on top of switch.
4. Check electric fuel pump operation as follows:
a. Connect pressure gauge T80L-9974-A or equivalent to fuel diagnostic valve on fuel rail.
b. Turn ignition key to On position and ensure gauge indicates 30---40 psi pressure.
c. Carefully disconnect fuel return line from fuel rail and position the fuel line in a calibrated container with a capacity of at least one quart.
d. Locate fuel pump relay and replace with a modified relay, Fig. 14.
e. Energize fuel pump for ten seconds, then allow fuel to drain into container.
f. The fuel pump is operating properly if; fuel pressure reaches 35---45 psi; the fuel flow is a minimum of 5.6 ounces in ten seconds and; fuel remains at a minimum of 30 psi immediately after shutdown.
g. If all three conditions are met, the fuel pump is operating properly. Check for engine and/or electrical malfunctions.
h. If pressure condition is met, but flow is not, inspect filters and fuel lines for obstructions and correct as necessary. If, after making necessary repairs, flow conditions are still not met, replace fuel pump.
i. If both flow and pressure conditions are met, but pressure drops off immediately after shutdown, check for leaking injectors or regulator. If injectors and regulator are satisfactory, replace fuel pump.
j. If no fuel flow or pressure is observed, repeat step 4h. If no trouble is found, replace fuel pump.
k. Replace modified fuel pump relay with original relay.