1 Valve needle
2 Solenoid valve spring
3 Solenoid valve
The fuel injectors are each fitted with one solenoid valve. Actuation for fuel metering is carried out by the IDM.
Current is applied to the solenoid valves in two stages. At the beginning of an injection process, the solenoid valve is actuated with a higher pick-up current (approximately 12 A) so that it opens quickly.
1 Current (in A)
2 Pick-up current
3 Holding current
4 Time
After a specified time, the pull-in current is reduced to a lower holding current (approximately 6 A). Unnecessary heat generation in the IDM is prevented in this way.
The injected fuel quantity is now determined by the opening period and the pressure in the fuel rail. The injection process finishes when the current supply to the solenoid valve is interrupted and the injector needle then closes.
Effects of faults
rough engine running
increased emissions of black smoke
loud combustion noise
Fuel pressure out of range.
Diagnosis
Monitoring includes recording of general faults during fuel metering (relating to all 4 cylinders) and of individual faults (relating to a cylinder).
By comparing the KS signal with the relevant timing map, it is possible to determine faults during the fuel metering as well as a complete failure of a fuel injector.
Faults, such as short circuits or open circuits in the wiring circuit of the fuel injectors, are determined by an electronic check in the PCM.
If a fuel injector has failed, the engine continues to run in emergency mode on three cylinders with reduced output.