AEK 1.6L and 6-cylinder engine
The Motronic system from BOSCH 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 a fuel filter to the fuel distribution manifold, and then to the valve injectors. A pressure regulator at the end of the distribution manifold maintains constant fuel pressure in the system. The valve injectors are electronically controlled and intermittently, that is, cyclically, inject fuel into the intake manifold before the intake valves.
The injection is not simultaneous. This means that the injectors are separated, controlled individually and inject fuel before the engine intake valves in accordance with the sequence of ignitions in the cylinders. By selecting the start of injection in relation to the opening moments of the intake valves, the engine's performance and environmental characteristics can be better controlled. In addition, the engine's responsiveness is improved.
Unlike the Digifant injection system, the Motronic system has a mass air flow meter instead of a volumetric flow meter. This flow meter has the following advantages: small dimensions, automatic compensation for the influence of temperature and altitude, no moving parts and therefore little wear. In the mass flow meter, a filament heated by an electric current is cooled by the flowing inlet air. In order to maintain the temperature of the hot filament constant, the heating current changes in accordance with the flowing air volume. Based on the change in heating current, the control unit determines the engine load mode and regulates the amount of fuel injected accordingly. To avoid distortion due to contamination, the filament is heated automatically after each engine shutdown.
The control unit regulates the injection duration and thus the amount of fuel injected in accordance with the signal from the air mass flow meter and the crankshaft speed. With a longer opening of the valve injector, more fuel is injected. Additional sensors and converters ensure that the amount of fuel injected is measured correctly in any driving situation.
(View the original on this portal VWmanual)
Sensors
The coolant temperature sensor is screwed into the coolant pipe above the thermostat (central sensor). In this case we are talking about a resistance thermometer (MTS-resistance), in which the resistance changes according to the coolant temperature and therefore also according to the engine temperature. The coolant temperature information serves as a correction factor for the ignition advance and injection duration for cold and hot engines. Other functions such as knock control and exhaust gas recirculation are activated at the corresponding engine temperature.
Intake air temperature sensor (only in engines with Motronic M2.9 system) screwed into the intake manifold on the left. The role of the sensor here is also performed by a resistance thermometer.
The ignition advance sensor is inductive, it is installed on the left side of the engine crankcase. The signal from the ignition advance sensor 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 Hall sensor. If there is no signal, the engine will not start.
The Hall sensor is located in the ignition distributor. The operating principle 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 engine cylinder at the moment of ignition together with the signal from the ignition timing sensor. If there is no signal, the control unit cannot recognize cylinders 1 and 6. In this case, the detonation control system includes a temporary program, which becomes noticeable by the loss of engine power.
The throttle potentiometer is located in the throttle valve 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 valve is in the idle position and at the same time the crankshaft speed exceeds a certain value, the control unit blocks the fuel supply to the engine.
The 1.6 litre engine (AEK) is equipped with one knock sensor, while the VR6 engine is equipped 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. Due to this, the fuel energy is used better, which simultaneously leads to a reduction in fuel consumption. The knock control system includes knock sensors and the corresponding analysis electronics. Due to the high compression ratio of the engine, knock combustion can occur, which, if prolonged, causes engine damage. To avoid this, knock sensors are required, which register combustion disturbances and ensure that the ignition timing is changed to a later one. If one knock sensor fails, the control unit automatically moves the ignition advance to a later position so that the engine is not damaged. If both sensors fail, the control unit switches on the time program and sets the maximum ignition advance of 11° before TDC for all cylinders. This is primarily due to the reduction in power, which also occurs when Super is used instead of unleaded petrol (AI 95 or AI 98) the fuel tank is filled with regular unleaded gasoline (AI 91).
The oxygen sensor is screwed into the catalytic converter housing. In cars with a regulated catalytic converter, it measures the oxygen content in the exhaust gases and sends a corresponding voltage signal to the control unit. Accordingly, the control unit changes the qualitative composition of the sucked-in fuel-air mixture so that the exhaust gases burn out optimally in the catalytic converter.
Idle speed control
LFR valve (Leertauffuellungsregelung) the LFR valve is installed between the intake air hose and the intake manifold. It regulates the air flow during idle operation, bypassing the throttle valve. This ensures that the crankshaft speed remains constant regardless of whether energy 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.
Caution: When working with injection systems, it is necessary to pay attention to impeccable cleanliness. Before dismantling, the corresponding parts must be cleaned with gasoline. The system is under high pressure. Therefore, before replacing parts, to reduce the pressure in the system, it is necessary to slowly loosen the fuel line fastening between the fuel pump and the filter. Preliminarily cover the fuel line with rags.
High blood pressure goes down on its own (without releasing the fuel line fastening) a few hours after the engine has been stopped.
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