Fuel Pressure Monitoring

.06.04.00 Fuel Pressure Monitoring

.06.05.00 General Description







(Example only)

Low fuel pressure system:
The low pressure system is the fuel delivery system to the high pressure system. In order to keep the delivery pressure in a certain range the fuel pressure is controlled via fuel pressure sensor. This low pressure system has no direct impact on Air/Fuel mixture and emissions.

High fuel pressure system:
The electrical controlled, mechanical-driven high pressure fuel pump provides the injection pressure. The fuel sensors and the control valve in the high pressure system controlled the high pressure between approximately 3 and 12 MPa. The target pressure depends mainly on engine speed and torque request.







.06.05.00 Monitoring function description

Technical Description of Pinpoint-Strategy for the High-pressure Fuel Injection System

A) Strategy description
The pinpointing-strategy is based on the fact that incorrect pressure information will cause Lambda deviations due to the pressure based calculation of the injection time.
Incorrect pressure information can only be caused by positive or negative offset-faults of the high pressure sensor.
However faults of the pump control valve also influence the pressure control activity but they will be normally completely corrected (Lambda deviation ~ 0) through the calculation of the corresponding injection time.

Through combination and evaluation of the following characteristics therefore a differentiation of faults and drifts between sensor and actuator is possible:
pressure deviation
pressure control activity
fuel trim activity

Pinpointing schematic







B) Definitions

Pressure deviation
Remaining difference between actual rail-pressure and nominal rail pressure (basically calculated on engine speed and torque request)

Pressure control activity
Total pressure control output consisting of proportional value, integral value and adaptation value. The total pressure control output influences the pilot control of the high pressure control valve in order to adjust the nominal pressure value.

Fuel trim activity
Correction factor of the Lambda-controller including the additive and multiplicative correction values of the fuel trim.

C) Basic requirements of the diagnostic routine:
pressure control unit active
fuel trim control unit active
no fault of the front and rear O2 sensors
no engine warm-up actions