1991 Isuzu Other Repair Question
1991 Isuzu Truck - starts only if you floor it?
Both fuel pump fuses are good and the fuel pump relay in engine compartment relay box is good. If I remove the relay and jumper constant battery voltage to the fuel pump, truck starts and runs as normal. My conclusion - relay is getting "crank" voltage" but not "run" voltage until RPM is high enough to trigger the switch-over. I'm guessing it's related to either oil pressure, crank position sensor or alternator output voltage? What should I look for next? Maybe just stop looking and shoot it??
Start your diagnosis by checking fuel pressure-just because you hear the pump it doesn't mean its working properly-the EFI doesn't like incorrect pressure/volume. If you have the correct pressure/volume check the injector/s are they clicking if not could be that the computer is not getting the crank signal in order to activate the injector/s.-could be the Cam/Crank sensors or the PCM ground driver.
Also could be a problem within the ignition system other than the Cam/Crank sensors.
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