How to Test the TPS Sensor on the 1990 Ford F-150
- 1). Turn the ignition key to the run position. Turn the digital volt/ohm meter on and set the controls for d/c volts. Verify that the 5-volt reference signal is present by touching the black meter lead to the engine block and piercing the orange wire on the TPS sensor wiring with the red meter lead. The meter should indicate approximately 5 volts. If there is no voltage, check and replace the fuses as needed.
- 2). Verify the sensor ground by piercing the black TPS wire with the red meter lead while touching the black meter lead to the engine. The voltage indicated by the meter should be less than .3 volts. This is a "voltage drop test." If the voltage is above .3 volts, clean the chassis ground connection on the fender well.
- 3). Verify that the signal return operates smoothly with no drop-outs as the throttle is opened slowly. Do this by piercing the green TPS wire with the red meter lead and touching the black meter lead to the engine. Have an assistant push the gas pedal slowly to the floor and slowly release it. The voltage indicated on the meter should sweep smoothly from .5 volts to 4.9 volts and back to .5 volts, without dropping to 0 volts or sticking at one voltage. Replace the sensor if the voltage drops to 0 or sticks during the test.
Source...