1.6.3.1 Monitoring Function - High Pressure System
High Pressure System Diagnosis: P302A, P302B, P302C, P302D,
Fuel Mass Plausibility Test: P3283, P3285, P3284, P3286
A high pressure fuel control system is necessary in order to prepare and to meter the fuel for gasoline direct fuel injection (DFI). The high pressure fuel pump increases the low fuel pressure from the fuel pump module inside of the tank. The fuel pressure is then adjusted to the desired fuel pressure set-point.
The high pressure fuel system consists of a common fuel rail for every high pressure piezo injection valve, a fuel rail pressure sensor, a high pressure fuel pump with a built-in fuel volume control valve, and an overpressure valve.
The high pressure needs to be adjusted to values between 5 MPa and 20 MPa. The value to which the high pressure is adjusted depends on the engine load and on the engine speed. Therefore, the fuel volume control valve (VCV) assists in measuring and in controlling the fuel rail pressure. The desired fuel-mass and the fuel pressure set-point value determine the pre-control, which in turn calculates the driver-signal for the fuel VCV. Closed loop control additionally controls this calculated driver-signal, utilizing the measured fuel pressure and the desired set-point value as input values.
The high pressure system diagnosis consists of a rationality test and, in principle, assesses the difference between the measured fuel pressure value, the set-point fuel pressure value, and the output value of the pressure controller. The long-term fuel trim output and the lambda controller are also taken into account when the calibratable threshold is reached. Pressure deviation is defined as the difference between the setpoint value and the measured value, i.e. pressure exceeding the set-point values leads to a negative deviation, and vice versa.
A non-adjustable fuel rail pressure that is too high is detected when the pressure deviation or the pressure controller output is below a calibrated (negative) threshold and one of the lambda control output values, either the lambda controller or the long-term fuel trim, is below a calibrated (negative) threshold. Specifically, the AFR tends to be too rich when left uncorrected. A malfunction is detected and a maximum fault high pressure system fault is set when these conditions are fulfilled for a calibrated period of time.
A non-adjustable fuel rail pressure that is too low is detected when the pressure deviation or the pressure controller output exceeds a calibrated threshold and one of the lambda control output values exceeds a calibrated threshold. Specifically, the AFR tends to be too lean when left uncorrected. A malfunction is detected and a minimum high pressure system monitoring fault is set when these conditions are fulfilled for a calibrated period of time.
The fuel mass plausibility diagnosis monitors the high pressure sensor signal plausibility.
A pressure sensor signal that is too high is detected when the pressure deviation or the output of the pressure controller drops below a calibrated (negative) threshold and one of the lambda control output values, either the lambda controller or the long-term fuel trim, exceeds a calibrated threshold. Specifically, the AFR tends to be too lean when left uncorrected. A malfunction is detected and a maximum fault high pressure system fault is set when these conditions are fulfilled for a calibrated period of time.
A pressure sensor signal that is too low is detected when the pressure deviation or the pressure controller output value exceeds a calibrated threshold and one of the lambda control output values, either the lambda controller or the long-term fuel trim, drops below a (negative) calibrated threshold. Specifically, the AFR tends to be too rich when left uncorrected. A malfunction is detected and a minimum high pressure sensor monitoring fault is set when these conditions are fulfilled for a calibrated period of time.