Volkswagen Corrado (1993 year). Manual - part 118

 

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Volkswagen Corrado (1993 year). Manual - part 118

 

 

E - THEORY/OPERATION 

         1993 ENGINE PERFORMANCE
         Volkswagen Theory & Operation - Motronic

         Corrado SLC

         INTRODUCTION

         This article covers basic description and operation of engine
performance-related systems and components. Read this article before
diagnosing vehicles or systems with which you are not completely
familiar.

         COMPUTERIZED ENGINE CONTROLS

         ELECTRONIC CONTROL UNIT

         The Motronic engine management system uses a single
Electronic Control Module (ECM) for fuel injection, idle speed
control, ignition, and emission controls. The Electronic Control
Module (ECM) continually corrects air/fuel mixture based on signals
from various signals. The ECM is located underneath center of
windshield cowl, directly behind engine compartment firewall.

NOTE:    Components are grouped into 2 categories. The first category
         covers INPUT DEVICES, which control or produce voltage
         signals monitored by the control unit. The second category
         covers OUTPUT SIGNALS, which are components controlled by
         the control unit.

         INPUT DEVICES

         Engine Coolant Temperature (ECT) Sensor
         Sensor is located on thermostat housing. As engine coolant
temperature increases, the resistance of the sensor decreases. Engine
coolant temperature sensor signals are used for control of ignition
timing, injector pulse width, and idle speed stabilization. In
addition, knock sensors, idle speed control, oxygen sensor and fuel
tank venting are activated based on coolant temperature.

         Engine Speed (RPM)/Reference Sensor
         Engine speed (RPM) and crankshaft position are registered by
a single sensor located on side of engine block. The sensor reads a
toothed wheel mounted on the crankshaft. The wheel has a 2-tooth gap
which is used as a reference point for crankshaft position. The engine
speed/reference signal is used to monitor engine RPM and to identify
TDC position of cylinder No. 1.

         Hall Effect Sensor
         See ELECTRONIC IGNITION SYSTEM under IGNITION SYSTEM in this

E - THEORY/OPERATION 

NOTE:    For component locations, see Fig. 1.

Fig. 1:  Motronic Component Locations (Corrado SLC)
Courtesy of Volkswagen United States, Inc.

         Intake Air Temperature Sensor
         Intake air temperature sensor is located on side of intake
manifold. The signal from this sensor is used for idle stabilization
and as a correction factor for ignition timing. If intake air
temperature sensor fails, the ECM uses a temperature of 68

ø

F (20

ø

C) as

a substitute value. If this happens, cold start problems could occur
at temperatures less than 32

ø

F (0

ø

C).

         Knock Sensor(s)
         See IGNITION TIMING CONTROL under IGNITION SYSTEM in this
article.

E - THEORY/OPERATION 

ø

F (180

ø

C) above air temperature.

         As airflow increases, the wire is cooled and the resistance
of the sensor changes. The resulting current change is converted to a
voltage signal and is used by the ECM to calculate the volume of air
taken in.
         If a fault develops with mass airflow sensor signal, the
signal from throttle valve potentiometer is used as a substitute in
order for the car to be driveable.

         Throttle Valve Potentiometer
         Throttle valve potentiometer (throttle position sensor) is
connected to throttle valve shaft. It informs the ECM about the power
requested by the driver (throttle opening). Idle and full throttle
switches are NOT used in potentiometer. Idle speed and full throttle
applications are recognized by the ECM from the voltage output of the
potentiometer.
         Throttle valve potentiometer signals are used for idle speed
stabilization, idle air volume control, fuel after-run shut-off, and
full throttle enrichment. The ECM uses mass airflow sensor signal and
engine RPM signals as substitute values if the potentiometer fails.

NOTE:    On automatic transmission equipped vehicles, the throttle
         valve potentiometer is combined in the housing with the
         potentiometer for transmission control.

         Oxygen (O2) Sensor
         The heated oxygen sensor is made from zirconium dioxide,
while the inner and outer surfaces are coated with platinum. If fuel
mixture is lean (excess oxygen), the oxygen sensor will send a low
voltage signal (about 100 millivolts) to the ECM. If fuel mixture is
rich (lack of oxygen), the oxygen sensor will send a high voltage
signal (about 900 millivolts) to the ECM.

         OUTPUT SIGNALS

NOTE:    Vehicles are equipped with different combinations of
         computer-controlled components. Not all components listed
         below are used on every vehicle. For theory and operation on
         each output component, refer to the system indicated after
         component.

         EGR Frequency Valve
         See EXHAUST GAS RECIRCULATION (EGR) SYSTEM under EMISSION
SYSTEMS in this article.

         Fuel Evaporative (Frequency) Valve
         See FUEL EVAPORATIVE EMISSIONS SYSTEM under EMISSION SYSTEMS
in this article.

E - THEORY/OPERATION 

         Fuel Pump
         See FUEL DELIVERY under FUEL SYSTEM in this article.

         Idle Air Control/Stabilizer Valve
         See IDLE SPEED under FUEL SYSTEM in this article.

         Ignition Coil & Output Stage
         See DISTRIBUTORLESS IGNITION SYSTEM (DIS) under IGNITION
SYSTEM in this article.

         Malfunction Indicator (CHECK ENGINE) Light
         See MALFUNCTION INDICATOR (CHECK ENGINE) LIGHT under SELF-
DIAGNOSTIC SYSTEM in this article.

         FUEL SYSTEM

         FUEL DELIVERY

         Fuel Pump
         A 2-stage fuel pump, located in fuel tank, is used (one motor
drives two separate pumps). The stage one vane-type pump draws fuel,
through a screen, from bottom of fuel tank and into an accumulator.
The vane-type pump acts as a transfer pump. The stage two gear-type
pump draws fuel from bottom of accumulator and out fuel lines.

         Fuel Pressure Regulator
         The diaphragm-type fuel pressure regulator is attached to
fuel return side of fuel rail. Fuel pressure is regulated depending on
intake manifold pressure. As intake manifold pressure changes, the
pressure regulator will increase or decrease fuel system pressure.

         FUEL CONTROL

         Fuel Injectors
         Fuel injectors are supplied with battery (system) voltage
through power supply relay and are controlled (grounded) by the ECM.
Injectors are opened sequentially in cylinder firing order. Fuel
quantity is determined by injector on time (duty cycle).

         IDLE SPEED

         Idle Air Control/Stabilizer Valve
         The idle air control/stabilizer valve is actuated by the ECM
thorough the valve's ground control circuit. When a defect in circuit
is recognized, both output stages are shut-off and the valve rotates
to a fixed potion. This permits engine to idle at a warm engine idle
speed.

         IGNITION SYSTEM

 

 

 

 

 

 

 

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