1.6L AEK engine and 6-cylinder engine
The BOSCH Motronic system is a combined ignition and injection system with a single control unit. In this chapter, I would like to focus mainly on the injection part of the system.
Fuel is sucked from the fuel tank by an electric pump and fed through the fuel filter to the fuel distribution manifold, and then to the valve injectors. A pressure regulator at the end of the manifold keeps the fuel pressure in the system constant. Valve injectors are electronically controlled and intermittently, that is, cyclically, inject fuel into the intake manifold in front of the intake valves.
Injection is not carried out simultaneously. This means that the injectors are decoupled, controlled individually, and inject fuel ahead of the engine's intake valves according to the firing sequence in the cylinders. By choosing the start of injection in relation to the opening times of the intake valves, the power and environmental qualities of the engine can be better controlled. In addition, the throttle response of the engine is improved.
Unlike the Digifant injection system, the Motronic system has a mass air flow meter instead of a volume flow meter. Such a flow meter has the following advantages: small dimensions, automatic equalization of the influence of temperature and altitude, no moving parts and therefore little wear. In the mass flow meter, the electrically heated filament is cooled by the flowing intake air. In order to keep the temperature of the hot filament constant, the filament current varies according to the amount of air flowing. By changing the glow current, the control unit determines the load mode of the engine and, in accordance with this, regulates the amount of injected fuel. To avoid distortion due to dirt, each time the motor is switched off, the filament glows automatically.
The control unit, in accordance with the signal from the mass air flow meter and the crankshaft speed, regulates the duration of injection, and thus the amount of injected fuehp a longer opening of the valve injector, more fuel is injected. Additional sensors and converters ensure that the amount of injected fuel is measured correctly in any driving situation.
Sensors
The coolant temperature sensor is screwed into the coolant pipe above the thermostat (central sensor). This is a resistance thermometer (MTS resistance), in which the resistance changes in accordance with the temperature of the coolant, and therefore in accordance with the temperature of the engine. The coolant temperature information serves as a corrective factor for ignition timing and injection duration when the engine is cold or hot. Other functions such as knock control and exhaust gas recirculation are activated at the appropriate engine temperature.
Intake air temperature sensor (only in engines with Motronic M2.9) screwed into the intake manifold on the left. The role of the sensor here is also performed by a resistance thermometer.
The ignition timing sensor is inductive and is installed on the left side of the engine crankcase. The ignition timing sensor signal is required when starting the engine in order to determine the TDC in the first cylinder of the engine at the moment of ignition together with the Hall sensor signal. If there is no signal, the engine will not start.
The Hall sensor is located in the ignition distributor. The principle of operation of the sensor is described in the description of the ignition system. The sensor signal is required when starting the engine in order to determine the TDC in the first cylinder of the engine at the moment of ignition together with the signal from the ignition timing sensor. In the absence of a signal, the control unit cannot recognize cylinders 1 and 6. In this case, the knock control system includes a time program, which becomes noticeable by the loss of engine power.
The throttle potentiometer is located in the throttle assembly. It determines the position of the throttle valve for the control unit. Thanks to this, in particular, the forced idle switch is controlled, since as long as the damper is in the position corresponding to idling, and at the same time the engine speed exceeds a certain value, the control unit blocks the fuel supply to the engine.
1.6L engine (AEK) equipped with one, and the VR6 engine with two knock sensors. Both knock sensors of the VR6 engine are located on both sides of the cylinder block: approximately between cylinders 1 and 3c on one side and between cylinders 4 and 6 on the other. The selective knock control system maintains the ignition timing at the knock limit and automatically adapts to the quality of the fuel used. Knock control allows the engine to have a high compression ratio. As a result, the energy of the fuel is better used, which at the same time leads to a reduction in fuel consumption. The knock control system includes knock sensors and associated analysis electronics. Due to the high compression ratio of the engine, knocking combustion can occur, which, after a certain duration, causes damage to the engine. To avoid this, knock sensors are required that detect combustion disturbances and take care to change the ignition timing to a later one. If one knock sensor fails, the control unit automatically advances the ignition advance to a later one so that the engine does not suffer damage. If both sensors fail, the control unit turns on the time program and sets the maximum ignition timing of 11°to TDC for all cylinders. First of all, this is due to a decrease in power, which also occurs when, instead of Super unleaded gasoline, (AI 95 or AI 98) c. the fuel tank is washed down with ordinary unleaded gasoline (AI 91).
The oxygen sensor is screwed into the catalyst housing. It measures the oxygen content in the exhaust gases in vehicles with a regulated catalyst and sprinkles the corresponding voltage signal on the control unit. In accordance with this, the control unit changes the qualitative composition of the intake air-fuel mixture so that the exhaust gases burn out optimally in the catalyst.
Idle control
LFR valve (Leertauffuellungsregelung) filling control system is installed between the intake air hose and the intake manifold. It regulates the air flow during idle operation bypassing the throttle. This achieves an engine speed that remains constant regardless of whether power consumers such as the power steering pump or the air conditioning compressor are switched on. The LFR valve is controlled by the electronic control unit of the injection system.
Attention: When working on injection systems, attention must be paid to impeccable cleanliness. Before dismantling, the relevant parts must be cleaned with petrol. The system is under high pressure. Therefore, before replacing parts to reduce pressure in the system, it is necessary to slowly release the fastening of the fuel line between the fuel pump and the filter. Cover the fuel line with rags first.
The high pressure drops on its own (without releasing the fuel line) several hours after stopping the engine.
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