On the 2004 Mercury Mountaineer with the 4.0L engine,The P0193 is a fairly straight forward code pointing to a problem with the Fuel Rail Pressure Sensor. It’s mounted to the driver’s side fuel rail, towards the front of the rail. Carefully inspect the electrical connector for any loose, broken or damaged wires. Inspect the vacuum line for any cracks, holes or disconnections. If the visual inspection checks ok, replacing the Fuel Rail Pressure Sensor should solve the problem. The fuel rail pressure (FRP) sensor 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. 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.
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