Fuel (Rail) Pressure Sensor
- What type of sensor is this? __________________________________________________________
- Is there a Test Plan available for the fuel pressure sensor? ____________________________
- Select Control Unit Functions (MED 9.2.1), Diagnosis Requests. Is there a status under the "Part Functions" column for observing the fuel pressure sensor? ___________________
- What are the pin and connector numbers at the ECM (1 or 2) for the fuel pressure sensor? Pin ___________________ Connector __________________
- Record the voltage value at this pin with the engine not running (ignition on). ______________ V
Engine running at idle speed. ______________ V
Engine speed at 2000 RPM. _______________ V
- Shut the engine off and turn the ignition back on "KL15" (engine not running). Observe the voltage value at this pin for approximately one minute. What did you observe?
____________________________________________________________________________
- If the pressure limiting valve is defective, could the answers to questions 5 and 6 (above) indicate this? _________________________________________________________________
Additional notes:
Return Shut-off Valve: The return shut-off valve prevents a pressure drop in the system while the engine is stopped and is located in the leakage line. When the engine is started, the valve is energized after a slight delay to prevent a pressure drop in the feed area of the high pressure pump (cavitation).
While the engine is running, this valve is supplied with system voltage (from the ECM Main Relay) and activated by the ECM providing a ground path which allows leakage fuel to return to the tank.
- High pressure pump
- Leakage line
- Return shut-off valve
Pressure Damper Vent Valve: The Pressure Damper Vent Valve provides a controlled outlet for fuel/vapors that accumulate in the Pressure Attenuator (damper) chamber in the top of each High Pressure Pump. This is a 3/2 way electrically controlled valve (KL15 from the IVM, ground path provided by ECM 1) that provides:
- A circuit for fuel to return to the fuel tank when energized (KL15 on) or
- A circuit for fuel vapors to vent into the evaporative system when de-energized (KL15 off)
When the engine is running, a slight amount of fuel may accumulate in the Pressure Attenuator upper chambers due to natural leakage through the internal diaphragm (extreme pressure). This fuel (circuit) is returned to the fuel tank by combining with the Leakage Line of the Return Shut-off Valve. The Pressure Damper Vent Valve provides a passage to combine these two circuits when the ignition is switched on (KL15) and isolates the Evaporative Emission circuit.
When the engine is not running, fuel vapors remain in these chambers and is routed into the Evaporative Emission circuit. This is accomplished by Pressure Damper Vent Valve blocking the passage from the Return Shut-off Valve (KL15 off) and opening a passage to the circuit leading from the Active Charcoal Canister to the Evaporative Emission Valve.
High Pressure Fuel Injectors (HDEV): The high pressure fuel injectors are designed essentially the same as conventional fuel injectors. They are secured by a taper in the cylinder head and sealed by a Teflon ring against the combustion chamber.
The O-ring seals the top of the injector and floats inside the brass coupling connections on the fuel rail. Each fuel injector incorporates a single hole nozzle with a spray angle of 70° to the piston crown.
To open the high pressure fuel injector, the nozzle needle is lifted off its seat when the solenoid coil is energized. Due to the high injection pressure (up to 120 bar), the pressure spring is designed to accommodate a pressure force of 30 newtons (5 newtons for conventional fuel injectors). The pressure spring forces the nozzle needle onto its seat during closing with sufficient contact pressure.