General Information and Safety Precautions

Layout of engine management system components, Simos. Engines 1.6 L 1 - Hall sensor connector (black) 2 - Hall sensor, under the timing belt upper cover 3 - oxygen sensor, 50 N, position at AT: in exhaust manifold 4 - oxygen sensor connector, underbody right side 5 - intake manifold switchover valve 6 - Simos control unit 7 - throttle valve control unit 8 - coolant temperature sensor 9 - mass air flow meter with intake air temperature sensor 10 - ground connection at manual gearbox 11 - ignition coils with output stage 12 - knock sensor connector 13 - engine speed sensor 14 - engine speed sensor connector (black) 15 - knock sensor 16 - injectors 17 - fuel pressure regulator 18 - charcoal canister 19 - canister purge solenoid valve

Location of Motronic engine management system components. Engine 1.8 L 1 - Solenoid valve for activated charcoal canister 2 - Connector for oxygen sensor (black) 3 - Intake air temperature sensor 4 - Throttle valve control unit 5 - Motronic control unit 6 - Camshaft adjustment valve 7 - Air mass meter 8 - Engine coolant temperature sensor 9 - Fuel pressure regulator 10 - Injectors 11 - Ignition coils, output stage 12 - Engine speed sensor 13 - Knock sensor 2 14 - Connector for knock sensor

2. 15 - Knock sensor 1 16 - Connector for engine speed sensor 17 - Connector for knock sensor

1. 18 - Hall sensor Note: From 8/97 production, an adjustable intake manifold with switching valve is additionally installed.

The electronic engine management system controls the amount of fuel supplied to the cylinders and controls the ignition process. Various control systems are used on the gasoline engines of the AUDI A3.

The electronic engine management system provides the following functions:

– Precise fuel metering in all operating modes, which ensures low fuel consumption with high power. – Reduction of harmful substances in the exhaust gas due to precise fuel metering and the use of a catalytic converter. – Self-diagnosis of the engine management system, which allows rapid fault finding. The engine management system has a fault memory. If a defect is detected during operation, it is stored in the control unit memory. If faults are present in the engine, a list of fault codes can be printed out, allowing the fault to be identified and rectified independently.

The engine control unit is a high-speed microprocessor. It determines the optimum injection timing and the quantity of fuel to be injected. The control unit also coordinates its operation with other vehicle systems, for example the automatic transmission control or the anti-theft immobilizer.

The engine management system components retain their high reliability over a long period and require virtually no maintenance. Only the air filter and spark plugs need to be replaced during routine service. Major adjustment and repair work requires complex diagnostic equipment and can only be carried out at an authorized service station.

Adjustment of idle speed and CO content is not required as part of routine maintenance.

Safety precautions when working on the engine management system / gasoline engine

The fuel system is under pressure! Fuel may spray out when the system is opened. Therefore, wipe up any spilled fuel with a rag. Gasoline vapors are poisonous and flammable. Wear safety glasses. Ensure good ventilation of the work area. Keep a fire extinguisher ready.

To avoid personal injury and/or damage to the injection and ignition system, observe the following:

– Do not touch or disconnect ignition leads while the engine is running or while the starter is engaged. – Connect and disconnect fuel injection lines and ignition leads, as well as electrical leads of measuring instruments, only with the ignition switched off. – Persons with a cardiac pacemaker must not work on the electronic ignition system. – Do not inject fuel while carrying out a compression test.

CAUTION

When working on the fuel injection system, observe the general safety and cleanliness rules.

Notes on checking the engine management system

– When troubleshooting, first read out the fault memory and check all vacuum connections for leaks. – For reliable operation of all electrical components, a voltage of at least 11.5 V is required. – If, after troubleshooting, repair or component testing, the engine starts only briefly and then stops, the cause may be that the anti-theft system is blocking it. In this case, read the fault memory and, if necessary, adapt the control unit.

Operation of the gasoline engine fuel injection system

Fuel is drawn from the fuel tank by the electric fuel pump and delivered through the fuel filter, mounted on the vehicle underbody, to the injectors. The fuel pressure regulator maintains constant pressure in the fuel system. Fuel is injected in metered quantities through electrically controlled injectors into the respective intake port directly upstream of the intake valves. The engine control unit controls the injection duration and thereby the quantity of fuel injected.

Air drawn into the engine passes through the air filter, the throttle valve and the intake manifold to the intake valves.

The air mass drawn into the engine determines the quantity of fuel injected. The air mass is measured by a special air mass meter. Inside the meter housing is a thin, electrically heated sensing element (hot-film) –1–, which is cooled by the air flowing past it. To keep the sensing element at a constant temperature, the current is varied in accordance with the air mass drawn in. The current value tells the control unit the engine load and thus regulates the quantity of fuel injected.

Location of hot-film sensing element 1 in the air mass meter

Information received from the various sensors and commands sent to the actuators ensure optimum engine operation under different operating conditions. If a sensor fails, the control unit switches to an emergency program to prevent engine damage and allow the vehicle to be driven further. Failure of a sensor does not necessarily affect engine operation. However, during any closer check of the exhaust gas composition, the fault memory of the engine management system must be read out.

Engine Management Sensors and Actuators

– The throttle valve is located in the central control unit, which gathers information from various sensors. The main task of the control unit is to stabilize idle speed under all engine operating modes and load conditions. The idle switch sends information about the idle position of the throttle valve to the control unit. The control unit opens or closes the throttle valve through an electric motor, thereby regulating the idle speed.

– The engine coolant temperature sensor and the intake air temperature sensor send information about the current temperature to the control unit based on changes in their electrical resistance. As the temperature rises, the resistance decreases.

– The fuel tank ventilation system consists of a charcoal canister and a solenoid valve. Fuel vapors generated in the tank due to fuel heating are stored in the canister. When the engine is running, fuel vapors are drawn from the canister and supplied to the engine.

– The oxygen sensor measures the oxygen content in the exhaust gases and sends a corresponding signal to the engine control unit.

– The knock sensor is used to determine the optimal ignition timing. In case of ignition malfunctions, fuel supply to the affected cylinder is cut off.

– Engines 1.8 L/125 L kW, engines 1.6 L have a variable intake manifold which changes the intake tract characteristics depending on engine speed. For this purpose, a flap with a pneumatic actuator is installed in the intake manifold. At low engine speeds, the long intake manifold provides good cylinder filling due to the resonance effect and thus high torque. At high engine speeds, the intake manifold is shortened, which allows the engine power potential to be used more fully.

– Engines 1.8 L/125 L kW: To obtain optimal engine power and torque over a wide speed range, the intake valve timing is adjusted depending on engine speed. Normally, the opening and closing timing is determined by the camshaft profile. To provide variable cam adjustment, the intake and exhaust camshafts are connected to each other by a chain. The hydraulic adjustment mechanism shifts the pivot point of the chain in the branch connecting the camshaft sprockets depending on engine speed. As a result, the phase of the intake valves is shifted relative to the exhaust valves. To increase torque in the low-to-medium speed range, the adjustment mechanism is engaged, and the intake camshaft opens and closes the valves earlier.

Fuel Injection System Checks – General Information

Only the basic electrical circuits of the fuel injection system can be checked independently.

If normal engine operation is disturbed, first check the condition of the electrical wiring and connectors. Check the condition of the air filter element, as well as the condition and electrode gap of the spark plugs. Check the crankcase ventilation hoses for blockage and the accelerator cable adjustment. If the engine still runs unstably, check the compression in the engine cylinders.

If a faulty injector is suspected, clean it.

If the engine still runs unstably, check the ignition system components.

If the malfunction is not yet eliminated, check the fuses and the condition of the electrical connectors and wiring. Electrical connectors must not have burnt contacts, moisture, signs of corrosion, dirt or other damage.

After carrying out self-checks, contact an authorized AUDI service station to diagnose the fuel injection system using specialized equipment.