Ford F150 Pickup. Manual — part 1625

Fuel Pump Monitor (Without Fuel Pump Driver Module)

The Fuel Pump Monitor (FPM) circuit is spliced into Fuel Pump Power (FP PWR) circuit and is used by PCM
for diagnostic purposes. PCM sources a low current voltage down FPM circuit. With fuel pump off, voltage is
pulled low by path to ground through fuel pump. With fuel pump off and FPM circuit low, PCM can verify
FPM and FP PWR circuits are complete from FPM splice through fuel pump to ground. This also confirms that
FP PWR or FPM circuits are not shorted to power.

With fuel pump on, voltage is supplied from fuel pump relay to FP PWR and FPM circuits. With fuel pump on
and FPM circuit high, PCM can verify FP PWR circuit from fuel pump relay to FPM splice is complete. It can
also verify that fuel pump relay contacts are closed and battery voltage is supplied to fuel pump relay.

Fuel Tank Pressure Sensor

See ENHANCED EVAPORATIVE EMISSION SYSTEM under FUEL EVAPORATIVE SYSTEM under
EVAPORATIVE EMISSION SYSTEMS.

Fuel Rail Pressure Sensor

On Crown Victoria 4.6L NGV, Fuel Rail Pressure (FRP) sensor is a diaphragm strain gauge device in which
resistance changes with pressure. See Fig. 20 . Electrical resistance of a strain gauge increases as pressure
increases, and decreases as pressure decreases. Varying resistance affects voltage drop across sensor terminals
and provides electrical signals to PCM corresponding to pressure. Strain gauge type sensors are considered
passive sensors. A passive sensor is connected to a voltage divider network so that varying resistance of passive
sensor causes a variation in total current flow. Voltage that is dropped across a fixed resistor in series with
sensor resistor determines voltage signal at PCM. This voltage signal is equal to reference voltage minus
voltage drop across fixed resistor.

FPDM

(1)

If a duty cycle meter and breakout box is used, be aware that these values may be reversed
depending on trigger setting of specific meter (for example, 25 percent from FPDM may read as 75
percent on duty cycle meter depending on trigger setting).

(2)

Some scan tools may not have capability to access FP_M PID. Percentage will fluctuate randomly. It
is okay for value to briefly go outside this range, then return.

(3)

Refer to FUEL PUMP under OUTPUT SIGNALS.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

Fig. 20: Identifying Fuel Rail Pressure Sensor (Crown Victoria 4.6L NGV)
Courtesy of FORD MOTOR CO.

On all others, FRP sensor measures pressure of fuel near fuel injectors. See Fig. 21 . This signal is used by
PCM to adjust fuel injector pulse width and meter fuel to each cylinder. FRP sensor senses pressure difference
between fuel rail and intake manifold. Return fuel line to fuel tank has been deleted in this type of fuel system.
Differential of fuel/intake manifold pressure together with measured fuel temperature provides an indication of
fuel vapors in fuel rail. Both differential pressure and temperature feedback signals are used to control fuel
pump speed. Fuel pump speed sustains fuel rail pressure which preserves fuel in its liquid state. Dynamic range
of fuel injectors increases because of higher rail pressure, which allows injector pulse width to decrease.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

Fig. 21: Identifying Fuel Rail Pressure Sensor (All Others)
Courtesy of FORD MOTOR CO.

Generator Load

The Generator Load Input (GLI) circuit is used by the PCM to determine generator load on the engine. As
generator load increases the PCM will adjust idle speed accordingly. This strategy helps reduce idle surges due
to switching high current loads. The GLI signal is sent to the PCM from the voltage regulator/generator. The
signal is a variable frequency duty cycle. Normal operating frequency is 40-250 Hz. Normal signal DC voltage
(referenced to ground) is between 1.5 V (low generator load) and 10.5 V (high generator load). See
GENERATOR LOAD INPUT under PCM CONTROLLED CHARGING SYSTEM under
MISCELLANEOUS CONTROLS.

Generator Monitor

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline

See GENERATOR MONITOR under PCM CONTROLLED CHARGING SYSTEM under
MISCELLANEOUS CONTROLS.

Heated Oxygen Sensor

Heated Oxygen Sensors (HO2S) are mounted in or right after exhaust manifold before catalytic converter
(upstream HO2S), and in exhaust pipe after catalytic converter (downstream HO2S). HO2S detects presence of
oxygen in exhaust gases and produces a variable voltage according to amount of oxygen detected. A high
concentration of oxygen (lean air/fuel ratio) in exhaust gases produces a low voltage signal less than 0.4 volt. A
low concentration of oxygen (rich air/fuel ratio) produces a high voltage signal more than 0.6 volt. HO2S
provides feedback to PCM indicating air/fuel ratio in order to achieve a near stoichiometric air/fuel ratio of
14.7:1 during closed loop engine operation. HO2S generates a voltage between 0.0 and 1.1 volts.

Embedded with the sensing element is the HO2S heater. The heating element heats sensor to 1400°F (800°C).
At approximately 600°F (300°C), engine can enter closed loop operation. VPWR circuit supplies voltage to
heater and PCM will complete the ground when the proper conditions occur. Starting in 1998, a new HO2S
heater and heater control system are installed on some vehicles. The high power heater reaches closed loop fuel
control temperatures. Use of this heater requires HO2S heater control be duty cycled, to prevent damage to
heater. The 6-ohm design is not interchangeable with new style 3.3-ohm heater.

Intake Air Temperature Sensor

Intake Air Temperature (IAT) sensors and integrated MAF type, are thermistor devices in which resistance
changes with temperature. See Fig. 22 and Fig. 23 . Electrical resistance of a thermistor decreases as
temperature increases, and increases as temperature decreases. Varying resistance affects voltage drop across
sensor terminals and provides electrical signals to PCM corresponding to temperature. Thermistor type sensors
are considered passive sensors. A passive sensor is connected to a voltage divider network so that varying
resistance of passive sensor causes a variation in total current flow.

2003 Ford Pickup F150

2003 ENGINE PERFORMANCE Theory & Operation - CNG, Flex-Fuel & Gasoline