F 250 4WD Super Duty V10-6.8L VIN S (2001)
Fuel Pressure Sensor/Switch: Description and Operation
FUEL RAIL PRESSURE SENSOR
Fuel Rail Pressure (FRP) Sensor
The Fuel Rail Pressure (FRP) sensor (Figure 31) is a diaphragm strain gauge device in which resistance changes with pressure. The electrical
resistance of a strain gauge increases as pressure increases, and decreases as pressure decreases. The varying resistance affects the voltage drop across
the sensor terminals and provides electrical signals to the 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 the resistance of
the passive sensor causes a variation in total current flow.
Voltage that is dropped across a fixed resistor in series with the sensor resistor determines the voltage signal at the PCM. This voltage signal is equal
to the reference voltage minus the voltage drop across the fixed resistor.
The FRP sensor measures the pressure of the fuel near the fuel injectors. This signal is used by the PCM to adjust the fuel injector pulse width and
meter fuel to each engine combustion cylinder.
Fuel Rail Pressure (FRP) Sensor
The Fuel Rail Pressure (FRP) sensor (Figure 32) senses the pressure difference between the fuel rail and the intake manifold. The return fuel line to
the fuel tank has been deleted in this type of fuel system. The differential fuel/intake manifold pressure together with measured fuel temperature
provides an indication of the fuel vapors in the fuel rail. Both differential pressure and temperature feedback signals are used to control the speed of
the fuel pump. The speed of the fuel pump sustains fuel rail pressure which preserve fuel in its liquid state. The dynamic range of the fuel injectors
increase because of the higher rail pressure, which allows the injector pulse width to decrease.
