Troubleshooting the fuel-injection system in the Ford Ranger can be a daunting task. Understanding how the system functions makes this system easier to diagnose and repair. High-pressure fuel is supplied to the fuel injector by the fuel pump. Just before and during the opening of the intake valve, an electrical pulse is sent to the injector and the injector opens to allow fuel to be sprayed into the cylinder. Diagnosing the system includes checking fuel supply and electrical function.
Attach the fuel-pressure tester gauge to the test port on the fuel rail attached to the injectors. Cycle the ignition key from off to on several times to pressurise the system. System pressure should be greater that 45 psi. If no fuel pressure develops in the system, the most likely causes are the fuel-pump fuse, fuel-pump relay, or fuel pump.
Check the fuel-pump fuse at the under-hood fuse block using the circuit tester. If the fuse is good, have a helper turn the ignition key to the start position and check for power supply at the fuel-pump electrical connector located near the rear of the fuel tank on the frame. If power is supplied to the pump but the pump doesn't come on, replace the pump. If no power is supplied to the pump, replace the fuel-pump relay. If fuel pressure is normal go to the next step.
Unplug one of the wiring-harness connectors attached to the fuel injectors. Plug the injector-harness tester into the harness connector. Have a helper turn the ignition key to the start position while you observe the tester. If the tester does not flash during cranking, check for power at the harness. One wire of the connector should be power and the other should be ground during cranking. Check the fuses if there is no power. Replace the ignition module if there is power supplied to the injector but no ground during cranking.
If the engine runs, but has a misfire, test the injector by measuring the resistance of the injector. Remove the wiring connector from the injector and touch the leads of the digital volt/ohmmeter to the pins in the injector. Readings of 0 ohms indicate a shorted injector and readings of infinite resistance indicate an open injector. Resistance values of 10 to 16 ohms are normal.