Part 8

14 COMPREHENSIVE COMPONENTS MONITORING Contd.

14.20 Fuel Rail Pressure Monitoring (FSI)

14.20.1 General description

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.

In order to adapt the flow rate of the fuel pump in a demand-controlled non-return flow fuel supply system to the consumption requirement of the engine, the fuel feed pressure is controlled by a pressure control valve and a low-pressure sensor. The low-pressure system supplies the high-pressure system with fuel.










Applicable only for test groups






High fuel pressure system
The fuel pressure required in the fuel rail for injection into the combustion chamber is generated by an electrical controlled, mechanical-driven high-pressure pump. To adapt the mass fuel flow of the high-pressure pump to the consumption requirement of the engine, the fuel pressure is controlled by means of a fuel rail control valve and a fuel system pressure sensor. The flow rate of the high-pressure pump depends on the camshaft speed and on the opening duration of the fuel-supply control valve.

The fuel rail control valve is an electrically controlled valve within the high-pressure fuel pump. The valve is located between the fuel-supply line and the pump chamber and regulates the mass fuel flow, thereby setting the pressure in the fuel distributor rail.

The fuel system pressure sensor is located on the fuel distributor rail, where it measures the fuel pressure.

The target fuel rail pressure (approximately between 3 and 11 MPa) depends mainly on engine speed and torque request.






The pinpointing-strategy for the high pressure system 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 fuel rail control valve also influence the pressure control activity but they will be completely corrected (Lambda controller deviation ~0) through the calculation of the corresponding injection time.
Through combination and evaluation of the pressure and lambda controller deviation characteristics therefore a differentiation of faults and drifts between fuel system pressure sensor and fuel rail control valve is possible:

Pressure controller deviation
Depending on deviation between target and actual pressure, the pressure control system becomes active. Total pressure control output consisting of proportional value, integral value and adaptation value. The total pressure control output influences the fuel rail control valve in order to adjust the nominal pressure value.

Lambda controller deviation
Lambda controller deviation determines the factor of the Lambda-controller including the additive and multiplicative correction values of the fuel trim.

Pinpointing schematic for high pressure system










Applicable only for test groups






14.20.2 Fuel pressure monitoring during cold start, Signal Range Fault P053F
Correct rail pressure has to be guaranteed during the catalyst heating phase for precise fuel injections. This setpoint fuel pressure during catalyst heating may be different from the setpoint fuel pressure without catalyst heating. Special high pressure monitoring is therefore utilized for cold start.

Monitoring Strategy
This function monitors differences between the actual and the setpoint rail pressure, which exceed a defined threshold.

Typical Enable Conditions
- Cold start high pressure adaptation for catalyst heating is active
- Time since engine start > defined threshold value
- Deceleration fuel cut-off not active
- Time since the end of the last deceleration fuel cut-off phase > defined threshold value

Malfunction Criteria
When the difference between the actual rail pressure and the setpoint rail pressure exceeds the upper or falls below the lower threshold value, a time counter is started. It remains active while either the lower or the upper threshold is exceeded, otherwise the counter is reset. A malfunction is detected, when the time counter exceeds a calibrated time threshold.






14.21 Fuel System Control Monitoring, low pressure side (FSI)

Applicable only for test groups






14.21.1 Fuel Pressure Too Low / High, P0089

Monitoring Strategy
The fuel pressure measured in the low pressure system is compared to the value defined by the engine control module. The difference between the setpoint value and the actual value is evaluated.

Typical Enable Conditions
- Time since engine start greater than defined threshold value

For Fuel Pressure too low monitoring only:
- Deceleration fuel cut-off not active
- Time since start of deceleration fuel cut-off greater than defined threshold value

Malfunction Criteria
The difference is calculated between the fuel pressure defined by the engine control module and the fuel pressure measured in the low pressure system.

If the absolute value of the difference between the setpoint value and the actual value exceeds a defined threshold value for longer than a defined fault confirmation time period, the pressure in the fuel low pressure system is detected as too low and a fault is registered.

If the absolute value of the difference between the setpoint value and the actual value falls below a defined threshold value for longer than a defined fault confirmation time period, the pressure in the fuel low pressure system is detected as too high and a fault is registered.






14.21.2 Adaptation Value of Fuel Pressure Control System too low / high, P0089

Monitoring Strategy
The adaptation value of the fuel system control (low pressure side) is compared to a defined threshold value.

Typical Enable Conditions
- Time since engine start greater than defined threshold value

Malfunction Criteria
For Adaption Value too low monitoring:
As the delivery rate of the fuel pump increases, the adaptation value of the fuel system control decreases. If the adaptation value falls below a defined threshold value for longer than a defined fault confirmation time period, an excessive delivery rate is detected and a fault is registered.

For Adaption Value too high monitoring:
As the delivery rate of the fuel pump decreases, the adaptation value of the fuel system control increases. If the adaptation value exceeds a defined threshold value for longer than a defined fault confirmation time period, an insufficient delivery rate is detected and a fault is registered.

14.22 Fuel System Pressure Sensor Monitoring, low pressure side (FSI)

Applicable only for test groups






14.22.1 Fuel System Pressure Sensor, Signal Range Fault, too high / low, P008B / P008A

Monitoring Strategy
The pressure signal of the fuel system pressure sensor is evaluated.

Typical Enable Conditions
- None

Malfunction Criteria
The pressure signal of the fuel system pressure sensor is checked for hydraulically rational values.
The upper limit value is determined by the opening pressure of the pressure limiting valve. If the pressure signal of the fuel system pressure sensor exceeds this upper limit value (threshold value), a fuel pressure is detected that is too high, and a fault is registered.
The lower limit value is determined by the smallest possible ambient pressure, since no vacuum is possible in the pressure line of the fuel system's low pressure side. If the pressure signal of the sensor falls below this lower limit value (threshold value), fuel pressure is detected that is too low, and a fault is registered.






14.23 Fuel Rail Control Valve Monitoring, high pressure side (FSI)

Applicable only for test groups






14.23.1 Fuel Pressure too low / high, P2293

Monitoring Strategy
The fuel pressure measured in the distributor rail is compared to the value defined by the engine control unit. The difference between the setpoint value and the actual value is evaluated.

Typical Enable Conditions
- Time since engine start greater than defined threshold value
- Deceleration fuel cut-off not active
- Time since deceleration fuel cut-off greater than defined threshold value

Malfunction Criteria
The difference is calculated between the fuel pressure defined by the engine control unit and the pressure measured in the distributor rail. If this difference exceeds or falls below a defined threshold value for longer than a defined fault confirmation time, the pressure at the high pressure side of the fuel system is detected as too low or as too high, and a fault is registered.






14.23.2 Fuel Rail Control Valve stuck closed / stuck open, P12A4 / P0087

Monitoring Strategy
The control action of the high pressure side of the fuel rail control system and the control action of the fuel mixture adaptation are each compared to the respectively defined threshold values. From the result both a stuck fuel rail control valve and a defective pressure sensor can be detected (pinpointing).

Typical Enable Conditions
- Engine speed greater than defined threshold value
- Evaporative system purge adaptation less than defined threshold value
- Engine coolant temperature greater than or equal to defined threshold value
- Intake air temperature less than defined threshold value
- Lambda control-loop closed
- Deceleration fuel cut-off not active

Malfunction Criteria
Fuel Rail Control Valve stuck closed
If the actual value measured in the fuel distributor rail by the fuel pressure sensor exceeds the calculated setpoint value, the fuel rail control system attempts to decrease the fuel pressure by appropriately intervening in the fuel injection pre-control system. If a fuel rail control valve is stuck closed, a large negative difference between the setpoint value and the actual value occurs and adjustment is not possible. In this case the correction value of the negative control action falls below a defined negative threshold value. However, in the case of a simple offset fault of the fuel rail control valve, the pressure can be adjusted so that the value does not fall below the defined threshold value.

Since a defective fuel pressure sensor of the high pressure side can also cause an intervention by the fuel rail control system, the correction factor of the lambda control is used as a second fault criterion. The injection time is calculated on the basis of the measured pressure in the fuel distributor rail. An excessive fuel pressure is compensated by a correspondingly shorter injection time. A stuck closed fuel rail control valve - resulting in too high fuel rail pressure - therefore has no effect on the lambda-based fuel mixture control. However, a false signal from the fuel pressure sensor leads to an incorrectly calculated injection time and consequently to an incorrect injected fuel amount. The result is a corresponding response of the lambda control system.

So, if the control action by the fuel rail control system including the P-part, the I-part and the adaptation part is less than a defined negative threshold, AND the control action of the fuel mixture adaptation including the additive and multiplicative mixture corrections remains within a defined range, a stuck closed fuel rail control valve is detected and a fault registered.

Fuel Rail Control Valve stuck open
If the actual value measured in the fuel distributor rail by the fuel pressure sensor falls below the calculated setpoint, the fuel rail control system attempts to increase the fuel pressure by appropriately intervening in the fuel injection pre-control system. If a fuel rail control valve is stuck open, a large positive difference between the setpoint value and the actual value occurs and adjustment is not possible. In this case the correction value of the positive control action exceeds a defined positive threshold value. However, in the case of a simple offset fault of the fuel rail control valve, the pressure can be adjusted so that the defined threshold value is not exceeded.

Since a defective fuel pressure sensor of the high pressure side can also cause an intervention by the high fuel rail control system, the correction factor of the lambda control is used as a second fault criterion. The injection time is calculated on the basis of the measured pressure in the fuel distributor rail. An insufficient fuel pressure is compensated by a correspondingly longer injection time. A stuck open fuel rail control valve - resulting in too low fuel rail pressure - therefore has no effect on the lambda-based fuel mixture control. However, a false signal from the fuel pressure sensor leads to an incorrectly calculated injection time and consequently to an incorrect injected fuel amount. The result is a corresponding response of the lambda control system.

If the control action by the fuel rail control system including the P-part, the I-part and the adaptation part is greater than a defined positive threshold value, AND the control action of the fuel mixture adaptation including the additive and multiplicative mixture corrections remains in a defined range, a stuck open fuel rail control valve is detected and a fault is registered.

14.23.3 Circuit Monitoring Fuel Rail Control Valve Power Stage

Short to Battery/Ground or Open Circuit

Monitoring Strategy
The voltage at the output of the fuel-supply control valve power stage is continuously monitored by the ECM.

Typical Enable Conditions
For short to ground:
- Control signal for the position "Closed" is present at the fuel-supply control valve

For short to battery:
- Control signal for the position "Open" is present at the fuel-supply control valve

For open circuit:
- Control signal for the position "Closed" is present at the fuel-supply control valve
- Control signal for the operating state "On" is present at the fuel pump

Malfunction Criteria

Short to ground, P2295:
If the voltage at the output of the fuel-supply control valve power stage in the ECM is less than a defined lower threshold value for a defined time period, a short to ground is detected and a fault is stored in the fault memory.

Short to battery, P2296:
If the voltage at the output of the fuel-supply control valve power stage in the ECM is greater than a defined upper threshold value for a defined time period, a short to battery is detected and a fault is stored in the fault memory.

Open circuit, P2294:
If the voltage at the output of the fuel-supply control valve power stage in the ECM is in a defined range for a defined time period, an open circuit is detected and a fault is stored in the fault memory.

Signal Transmission Fault

Monitoring Strategy
The signal transmission is continuously monitored.

Typical Enable Conditions
- Control signal for the position "Closed" is present at the fuel-supply control valve

Malfunction Criteria
Signal transmission fault, P2294:
If a fault is detected by the internal signal monitoring function, an entry is made in the fault memory.