COMPONENT TESTING
Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures
A frame-mounted pump is used on vehicles with 2.3L and 5.0L EFI engines. This high pressure (up to 39 psi) pump is frame-mounted, and can supply up to 15.9 gallons (60 liters) of fuel per hour. A pressure relief valve, mounted internally, protects against over-pressurization of system if fuel flow is restricted.
Vehicles with 7.5L engines use a submerged, in-tank fuel pump, designed to prevent loss of fuel flow during off-road use. Vehicles with 5.0L EFI use both a frame-mounted and an in-tank pump.
Inertia Switch
If vehicle in involved in a collision or rollover, an inertia switch will stop fuel flow. Engine will run until present fuel supply is exhausted. After that point, inertia switch must be reset before vehicle can be restarted. To reset switch (located under instrument panel), depress button on switch.
Fuel Selector Valves
For information on operation and testing of fuel selector valves, see FUEL SELECTOR VALVE article in FUEL section.
Frame-Mounted Pump
- Check fuel tanks for adequate fuel supply, do not assume fuel gauge is correct. Check for fuel leakage at fittings and lines. Locate fuel pump connector at end of "short harness" (wiring between pump body harness). Remove connector and check continuity between connector terminals.
- If continuity is 5 ohms or less, go to step 5. If continuity is 5 ohms or more, check for continuity between ground lead of connector and ground. If continuity is not present, repair open in pump ground circuit and recheck system operation. If continuity is present, go to next step.
- Check for continuity between Pink/Black wire of connector and ground. If continuity is present, repair short in pump power wiring circuit and recheck system operation. If continuity is not present, go to next step.
- Check continuity across pump terminals. If continuity is present, go to step 5. If continuity is not present, check pump sender wiring. If wiring is okay, replace pump sender assembly and recheck system operation.
- Check for voltage between Pink/Black wire of connector and ground, while turning ignition on. Voltage should be 12 volts momentarily, then drop to 0 volts. If voltage is not correct, check pump power circuitry and repair as required.
- Check for continuity between leads of "short harness". If continuity is present, remove "short harness" leads at pump and check continuity across pump terminals. If continuity is not present, replace pump. If continuity is present, replace "short harness".
In-Tank Pump - 7.5L Engines
- Check for adequate fuel supply, do not assume fuel gauge is correct. Check for fuel leakage from lines and fittings. Replace lines and/or fitting as necessary.
- Remove fuel pump cut-off relay connector. Check for voltage between Yellow wire at connector and ground. If 12 volts are present, go to step 3. If voltage is not present, check inertia switch. Reset switch if necessary.
- Connect voltmeter between Pink/Black wire of connector and ground. Crank engine momentarily, and note voltage reading. If 10-12 volts are present while cranking, go to step 4. If voltage is less than 10 volts, check fuse link and resistance wiring.
- Check for continuity between Pink/Black wire and ground. If continuity is present, reinstall relay and go to step 5. If continuity is not present, check tank selector relay (if equipped). If relay is okay, or is not used, check continuity across fuel pump terminals.
- If continuity is present across both the terminals and wiring harness, go to step 6. If continuity is present across pump terminals, but not wiring harness, replace pump sender assembly. If continuity is present across wiring harness, but not pump terminals, replace pump and recheck system operation.
- Attach relay connector. Connect voltmeter leads between Pink/Black wire and ground. Crank engine momentarily (until oil pressure is built up), and note voltage reading.
- Turn ignition back to "RUN" position, and note voltage reading. If voltage (10-12 volts) remains steady, check fuel pump flow capacity. See FUEL PUMP TESTING (IN-TANK) in this article. If voltage (10-12 volts) does not remains steady, or never existed, check relay circuit and oil pressure switch.
MODIFYING FUEL CUT-OFF RELAY
- Using new Relay (E3EB-9345-BA, CA, DA or E3TF-9345-AA), drill a 1/8" hole in-line with pins, and as close to pins as possible. NOTE: Part of relay skirt may be cut away to provide easier access to pins.
- Solder a 16-18 gauge jumper wire between pins "2" and "4". (Scheme 20) Feed end of a long (8-10'), insulated, flexible wire through hole drilled in relay skirt, and solder end to exposed base of pin No. "1" (as close to relay base as possible). This will permit full insertion of relay into socket. Solder an alligator clip to other end of long flexible wire.
Scheme 20
- With assistant in vehicle, raise vehicle on hoist. Locate fuel diagnostic valve. If diagnostic valve is present, go to step 2. If pump does not have diagnostic valve, fabricate test line and fitting assembly. (Scheme 21) (Scheme 20): Modifying Fuel Pump Cut-Off Relay Solder long wire as close to relay base as possible.
- Attach gauge to diagnostic valve (or test line and fitting assembly). Turn ignition on and check pressure reading. Reading should be 30-40 psi, if pump is operating properly and other system components are okay.
- Disconnect fuel return line at fuel rail. Use care to avoid fuel spillage. Route hose from fuel rail fitting to a calibrated container of at least 1 quart capacity.
- Replace fuel pump relay with modified relay. See MODIFYING FUEL CUT-OFF RELAY in this article. Place end of return hose into calibrated container. Route long wire to vehicle ground. Pump should now operate. Run fuel pump for 10 seconds.
- Observe fuel flow volume and pressure. Fuel pump is operating properly if fuel pressure is 35-45 psi, fuel flow is a minimum of 5.6 oz. in 10 seconds and fuel pressure remains at a minimum of 30 psi immediately after pump stops.
- If all 3 conditions are met, fuel pump is operating normally. If conditions are not met, check for engine and electrical problems. If okay, go to next step.
- If fuel pressure meets specification, but fuel flow does not, check for blocked filter(s), fuel supply lines, and/or tank selector valve. After correcting any blockages, repeat above tests. If fuel flow still does not meet specification, replace pump.
- If both fuel pressure and fuel flow meet specification, but system will not stay pressurized after pump is turned off, check for leaking injectors or regulator. If they are both okay, replace fuel pump. If no fuel flow or fuel pressure is observed, fuel system should be checked as in step 7. If system is okay, replace fuel pump.
Scheme 21
- Open fuel line at high pressure pump inlet. Connect hose to line from fuel tank. Route hose to a 1 quart, calibrated container. Disconnect high pressure fuel pump electrical connector from body wiring harness.
- Replace fuel pump relay with modified relay. See MODIFYING FUEL CUT-OFF RELAY in this article. Ground wire coming from relay to a convenient ground point to energize fuel pump and measure flow for 10 seconds. (Scheme 21): Test Line And Fitting Assembly Apply pipe sealant to fittings. NOTE: It may be necessary to momentarily block fuel hose to prime low pressure pump with outlet open and no back pressure on outlet; this is normal.
- If fuel pump produces a minimum flow of 16 oz. of fuel, within 10 seconds, pump is operating correctly. If there is no flow from pump, check electrical circuit and check for inlet restriction. If electrical circuits are okay and inlet is not restricted, replace pump.
In-Tank Pump - 7.5L Engine
- Disconnect fuel line just before vapor separator. Route end of hose to a calibrated container of at least 1 quart capacity. Turn ignition on, but do not start engine. Create a short condition across oil switch terminals. Run fuel pump for 10 seconds. NOTE: To initiate fuel flow, it may be necessary to momentarily block the hose to create a back pressure condition.
- If 16 oz. (473 ml) of fuel, or more, flows from pump during 10 second test, pump is okay. If fuel flow does not meet specification, check for the following conditions; a blockage or restriction in fuel lines, a blockage or restriction in fuel filter, or spare tire pinching inlet line of fuel pump. If all 3 conditions are okay, replace pump sender assembly.
6 PORT FUEL SELECTOR VALVE (EXCEPT WITH HOT FUEL HANDLING)
The system used on these vehicles consists of fuel selector valve, and a fuel tank selector switch.
Power is supplied to the fuel tank selector switch from the fuse panel when the ignition switch is in the RUN or START position. This power goes through the fuel tank selector switch and then directly to the motorized fuel tank selector valve.
With the fuel tank selector switch in the front tank position, power is supplied from the selector switch to terminals 2 and 4 of the motorized fuel valve. The ground path is completed through terminals number 1 and 3 of the fuel tank selector valve and is grounded through the selector switch. This causes the valve to actuate, opening the ports to the front tank and allowing fuel to flow through the fuel line to the engine.
When the fuel tank selector switch is moved to the rear tank position, power is supplied from the selector switch to terminals number 1 and 4 of the motorized fuel valve. The ground path is completed through terminals number 2 and 3 of the fuel valve and is grounded through the selector switch. This current path causes the valve to actuate opening the ports to the rear tank and allowing fuel to flow through the fuel line to the engine. The valve also directs excess fuel, returning from the engine, to the same tank from which fuel is being pumped. Fuel valve terminals 3 and 5 are connected to the front fuel tank sender and the rear fuel tank sender respectively. Terminal 4 feeds the fuel gauge. In the front tank mode an internal switch connects terminal 3 to terminal 4 thus supplying the front tank sender signal to the fuel gauge. Terminals 3 and 5 are connected in the rear tank mode.
6 PORT FUEL SELECTOR VALVE (WITH HOT FUEL HANDLING)
The system used on these vehicles consists of fuel selector valve, and a fuel pump cutoff relay, tank selector relay, inertia switch, fuel tank selector switch, and in-tank electric fuel pump/sender.
Power is supplied to the fuel tank selector switch from the fuse panel when the ignition switch is in the RUN or START position. This power goes through the fuel tank selector switch and then directly to the motorized fuel tank selector valve.
With the fuel tank selector switch in the front tank position, power is supplied from the selector switch to terminal 2 of the motorized fuel valve. The ground path is completed through terminal number 1 of the fuel tank selector valve and is grounded through the selector switch. This causes the valve to actuate, opening the ports to the front tank and allowing fuel to flow through the fuel line to the engine.
When the fuel tank selector switch is moved to the rear tank position, power is supplied from the selector switch to terminal number 1 of the motorized fuel valve. The ground path is completed through terminal number 2 of the fuel valve and is grounded through the selector switch. This current path causes the valve to actuate opening the ports to the rear tank and allowing fuel to flow through the fuel line to the engine. The valve also directs excess fuel, returning from the engine, to the same tank from which fuel is being pumped. Fuel valve terminals 3 and 5 are connected to the front fuel tank sender and the rear fuel tank sender respectively. Terminal 4 feeds the fuel gauge. In the front tank mode an internal switch connects terminal 3 to terminal 4 thus supplying the front tank sender signal to the fuel gauge. Terminals 3 and 5 are connected in the rear tank mode.
Power is supplied to either the front tank or rear tank electric fuel pump by the fuel pump selector relay. Terminal number 2 of this relay is electrically connected to terminal number 2 on the fuel tank selector switch. (This causes the front pump to run only when the front tank is selected and the rear pump to run only when the rear tank is selected). Relay terminal number 1 is connected to ground to complete the relay coil circuit. Relay terminal number 4 supplies power to the front tank pump and terminal number 5 supplies power to the rear tank pump.
The input power to selector relay terminal number 3 is provided by two sources; direct from the starter solenoid during the crank mode only, or through a 0.75 ohm resistance wire connected to terminal number 3 of the fuel pump cutoff relay. The resistance wire reduces slightly the voltage supplied to the in tank pump during normal operation. The fuel pump cutoff relay coil receives its power through terminal number 2 from an engine activated oil pressure switch which is closed only when the engine is running and the relay coil is grounded through terminal number 1. Power to run the fuel pumps is supplied through an inertia switch to terminal number 4 of the fuel pump cutoff relay.
Emission System
Physical damage, leaks, and missing items are the major answers to diagnosis of emission system complaints. Fill cap damage or contamination that renders the pressure-vacuum valve inoperative may result in deformation of the tank. Care should always be exercised to be sure that a proper fill cap (in working order) is used.
Fuel Selector Valve
For the following diagnostic procedures, both tanks must contain some usable fuel.
Note. Diagnostic procedures for the 5.0L EFI Engine with dual tanks was not available.
Removal & Installation (Frame-Mounted Pump)
Disconnect "short harness" wiring at pump. Disconnect fuel line fittings. Unbolt 3 bolts attaching pump to frame. To install, reverse removal procedure. Start engine and check for leaks.
Removal & Installation (In-Tank Pump)
- Disconnect battery negative cable. Raise and support vehicle. Remove fuel tank. Turn sending unit lock ring counterclockwise and pull ring away from tank. (Scheme 22)
- Lift fuel lever sending unit and pump assembly from tank. Note position of alignment tabs (if equipped). Remove pump from sending unit. To install, reverse removal procedure. Start engine and check for leaks.
