All fuel pumps will be either the mechanical or electrically operated design. Most carbureted vehicles use an engine-mounted mechanical pump.
Gasoline engine vehicles with fuel injection use an electric fuel pump to supply higher pressure demands required with these systems. Electric fuel pumps are normally located in or near the fuel tank. Some models use a low pressure and a high pressure electric pump. Generally, one pump will be located in the fuel tank, and the other externally.
When trouble shooting fuel pumps, remember that electric fuel pumps do not operate unless a reference signal is received from the distributor. Verify that the unit has enough pressure, volume, and vacuum (suction). When found defective, it is recommended that the fuel pump be replaced as an assembly.
INERTIA SWITCH
Fuel injected models use an electrical interrupt switch in the fuel system. This inertia switch disables the fuel delivery system when the vehicle is struck violently or when vehicle roll-over takes place.
OPERATION
In the event of a collision or vehicle roll-over, electrical contacts within the inertia switch shut off fuel supply to the electric fuel pump. Fuel supply will be interrupted even if the engine is still running. Switch contacts are normally closed, but open upon impact or roll-over. A reset button is located on the switch assembly. If the electrical circuit trips, it is not possible to re-start the vehicle unless the switch is reset by depressing the reset button. Anytime the switch opens, the fuel system should be inspected for damage prior to resetting.
On LTD Crown Victoria and Grand Marquis station wagon models, switch is located in left rear side storage compartment.
On Mustang, it is located near left taillight.
On Taurus and Sable station wagon models, switch is located behind access door in right rear cargo area.
On all other vehicles, inertia switch is located in trunk, on left hinge support or behind trim panel.
Scheme 7
Scheme 8
INSPECTION & TESTING
| CAUTION | Electric fuel pump systems are under constant pressure. The pressure must be released BEFORE any part of fuel system is disconnected. To relieve pressure, remove fuel pump fuse and run engine until it stops. |
FUEL LINES & HOSES
Inspect all metal fuel lines for damage caused by vibration, impact, or kinking. Inspect rubber hoses for cracks, kinks, or deterioration. If fuel line between engine and fuel tank is suspected of being clogged, disconnect at engine and fuel tank and blow clear with compressed air. NEVER use compressed air on a fuel line unless the line is disconnected at both ends.
Typical Mechanical Fuel Pump. Scheme 9
FILTERS & SCREENS
Clean or replace all filters and screens located in the fuel line circuitry. Inspect carburetor/throttle body assembly for filters or screens and clean or replace as necessary. In some cases, fuel tank pick-up screen can be clogged enough to affect fuel delivery at high speed.
WIRING CONNECTIONS
Inspect all wires and electrical connections for breaks, loose connections and corrosion. Faulty fuel pump wiring or connections can cause inaccurate testing and diagnosis results.
Mechanical
- Check fuel supply to verify sufficient gasoline in the tank. Disconnect ignition wire from distributor so that engine will not start.
- Separate fuel line at carburetor inlet fitting. Install a piece of fuel resistant hose over the end of fuel line. Place end of hose into a gasoline container.
- Crank engine to activate fuel pump. The amount of fuel pumped will vary according to each manufacturer. The average pump output should be about one pint in 30 seconds.
- If little or no gasoline flows from hose, check fuel lines or gasoline tank filter for restrictions or leaks. If lines and filter are clear, pump is defective and must be replaced.
Electrical
Note. The following is only a general procedure. For specific manufacturer's electric fuel pump testing procedures, see appropriate FUEL INJECTION article in this section.
- Most vehicles use a fitting to allow pressure test without separating fuel lines. If not, separate fuel line from injector inlet "T". Install a "T" connector with a pressure gauge in the line and reconnect line to injector.
- Hold pressure gauge about 16" above fuel pump. Start engine and observe pressure.
- After pressure check, reconnect steel line. If pressure is not within specifications or varies greatly, replace fuel pump.
FUEL PUMP SPECIFICATIONS TABLE
| Application | Psi (kg/cm 2 ) | |
|---|---|---|
| Electric Fuel Pump | ||
| 1.9L, 2.3L OHC, 2.3L Turbo, 3.0L, 3.8L MPFI | 35-45 (2.5-3.1) | |
| 1.9 & 2.5L CFI | 13-17 (.9-1.1) | |
| 2.3L HSC MPFI | 50-60 (3.5-4.2) | |
| 5.0L SEFI | 35-45 (2.5-3.1) | |
FUEL PUMP SPECIFICATIONS
- Disconnect fuel line from carburetor. Connect line to a pressure gauge. Hold gauge about 16" above pump level.
- Start engine and allow to idle (using gasoline in carburetor bowl). Observe pressure gauge. Pressure should be about 4-7 psi (.28-.49 kg/cm 2 ) for 4-cylinder and V6 engines, and about 6-9 psi (.42-.63 kg/cm 2 ) for V8 engines.
- If pressure is too low, check fuel lines or gasoline tank filter for restrictions or leaks. If lines and filter are clear, pump is defective. If pressure is incorrect or varies greatly with the engine speed, replace the fuel pump.
Scheme 10
- Reconnect fuel line to carburetor inlet and check for leaks. Disconnect hose at inlet side of fuel pump. Raise end of hose so fuel will not run out. Connect vacuum gauge to pump inlet with short length of hose.
- Start engine and allow to idle. Check vacuum level. Gauge should read at least 5-7.7 in. Hg (Ford Motor Co.). (Scheme 10): Typical Ford Electric Fuel Pump