Fuel Pressure: Testing and Inspection
The following tests can be used to determine if the fuel pump is operating properly.
1984 Continental, Cougar, Mark VII & Thunderbird; 1984---85 Capri & Mustang; 1984---86 LTD & Marquis
1. Check for adequate fuel supply. Tank must be at least half full.
2. Check for fuel leakage at all lines and fittings.
3. Check continuity to fuel pump as follows:
a. Disconnect electrical connector to fuel pumps at high pressure pump module, then connect voltmeter to body wiring harness connector.
b. Turn ignition switch to the ``On'' position, while watching voltmeter.
c. Voltage should rise to battery voltage, then return to zero voltage after approximately one second. If voltage is not as specified, check inertia switch and electrical system for proper operation.
d. Connect ohmmeter to pump wiring harness connector. If no continuity is present, check continuity directly at pump terminals.
e. If continuity is not present at pump terminals, replace pump. If continuity is present at the terminals but not at pump wiring harness connector, repair or replace wiring harness.
f. Connect ohmmeter across body wiring harness connector. If continuity is approximately 5 ohms, low pressure pump circuit is satisfactory. If no continuity is present, check for continuity at fuel pump sender flange terminals. If continuity is not present, replace assembly.
4. Check electric fuel pump operation as follows:
a. Disconnect return line at fuel rail, then connect hose from fuel rail fitting to a calibrated container of at least one quart capacity.
b. Connect pressure gauge T80L-9974-A or equivalent to fuel diagnostic valve on fuel rail.
c. Disconnect fuel pump electrical connector located forward of pump outlet.
d. Connect auxiliary wiring harness to the electrical connector to fuel pump.
e. Energize fuel pump for 10 seconds by connecting auxiliary wiring harness to a fully charged 12 volt battery and note pressure. If no pressure is present, check polarity of wiring harness and terminal connectors at fuel pump.
f. Allow fuel to flow into container while observing capacity. The fuel pressure reached should be 35---45 psi and the fuel capacity should be a minimum of 9.5 oz. in 10 seconds. Fuel pressure should remain steady at 30 psi immediately after de-energizing the fuel pump. The fuel pump is operating normally if the above conditions are met.
g. If specified pressure in step 4f is obtained, but volume is below specifications, check for obstructions in fuel filters or supply lines. After making necessary corrections, repeat steps 4e and 4f. If volume is not as specified, replace pump.
5. If hot fuel problems exist or system is noisy, check low pressure in-tank fuel pump as follows:
a. Remove inlet push connect fitting and line from high pressure pump assembly. Raise end of fitting above level of fuel in tank to prevent siphon action.
b. Connect hose from fuel tank to a calibrated container of at least one quart.
c. Place ignition switch in ``Run'' position for approximately one second until fuel pump relay stops operation.
d. Check container for a minimum fuel flow of 1.5 oz. If no fuel is present, repeat steps c and d two or three times. If fuel is still not present, check for pinched line between fuel tank and fitting.
e. Connect voltmeter to chassis electrical connector to fuel pump, then turn ignition switch to ``On'' position. Voltage should rise to battery voltage for approximately one second, then return to zero volts.
f. If voltage is as specified and electrical connector at pump is satisfactory, replace fuel pump assembly and repeat test. If no voltage is present, check vehicle electrical circuit.
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.