INTRODUCTION
This article covers the basic description and operation of engine performance related systems and components. Prior to diagnosing vehicles or systems with which not you are completely familiar, read through this article.
200 & 200 Quattro 2.2L Turbo
A water-cooled turbocharger is mounted directly to the exhaust manifold. The turbocharger assembly consists of turbine/compressor assembly, oil supply system and wastegate. The wastegate functions as a safety valve to prevent excessive intake boost pressure. Other components include impellers, impeller shaft, bearings and impeller housings.
At idle and light throttle, the turbo charged engine operates as a standard engine. When additional power is required, exhaust gases from exhaust manifold enter the turbocharger's turbine housing and flow through the turbine blades.
Exhaust flow and turbine speed increase as throttle opens and RPM increases. The impeller turns with turbine and forces air into compressor housing and intake manifold. As impeller and turbine speed increases, boost pressure also increases.
Turbocharger operation requires large quantities of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to the system.
CIS Digital Control (DC) system uses continuous injection system with Lambda for electronic control of mixture adjustment, emissions and ignition timing. An indicator light on dash illuminates if detonation becomes continuous or a fault is detected in circuitry.
Electronic controls consist of intake manifold pressure sensor (built into ECU), air temperature sensor, coolant temperature sensor, Electronic Control Unit (ECU), crankshaft speed sensor, crankshaft reference sensor, Hall Effect switch, knock sensor, throttle valve switch, brake switch, engine overheat sensor and oxygen sensor.
The ECU uses input from these sensors to control cold start valve, oxygen sensor heater, cold engine warm-up enrichment, Lambda control (frequency) valve, transistorized ignition coil, wastegate frequency valve, charcoal canister shut-off valve, fault warning light and ignition timing control.
90, 80/90 Quattro 100 & 100 Quattro 2.3L
System uses 2 interfacing computers. An Ignition Control Unit (ICU) controls ignition timing. When the ICU employs a knock sensor, the control unit is termed a Knock Sensor Control Unit (KSCU). The Fuel Injection Control Unit (FICU) controls fuel injection. CIS-E III system also has self diagnosis and trouble shooting capabilities.
Input and output signals from various sensors, switches and signalling devices are constantly monitored for faults. These faults are stored in memory. Faults can be displayed by a flashing 4-digit code sequence from an LED located on the instrument cluster.
80 2.0L
System uses single Electronic Control Unit (ECU), which controls fuel delivery, ignition system and operation of emission control components. System has self-diagnostic capabilities and input signals from various sensors, switches and signaling devices are constantly monitored for faults. These faults are stored in memory and can be displayed by a flashing 4-digit code sequence from the "FAULT INDICATOR LIGHT" (FIL), located in instrument cluster.
CONTROL UNIT
On CIS Motronic and CIS Digital Control (DC) system, the control unit is referred to as the Electronic Control Unit (ECU). On the CIS-E III system, 2 interfacing computers are used and are referred to as the Ignition Control Unit (ICU), and Fuel Injection Control Unit (FICU). When a knock sensor is used in the system the control unit is referred to as a Knock Sensor Control Unit (KSCU).
In operation, the control unit receives signals from the air sensor potentiometer, oxygen sensor, coolant temperature sensor, throttle valve switches,O2 sensor and other sensors specific to the individual system. Using this data the control unit varies air fuel mixture and ignition timing to maintain optimum performance, fuel economy and emission standards.
Scheme 1
Scheme 2
Scheme 3
Note. For ease of understanding, components are grouped into 2 categories. The first category, INPUT DEVICES, is components which control or produce voltage signals that are monitored by the ECU. The second category, OUTPUT SIGNALS, are components that are controlled by the ECU (this is usually accomplished by the ECU grounding individual circuits).
INPUT DEVICES
All vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input usage on a specific model, see WIRING DIAGRAMS article. The available input signals include the following
Air Sensor Potentiometer
Air sensor potentiometer generates a voltage signal based on position of airflow sensor plate. Depending on the particular system, the Fuel Injection Control Unit (FICU) or Electronic Control Unit (ECU) uses this signal to determine cold acceleration enrichment.
The Ignition Control Unit (ICU) or ECU, (depending on particular system), uses information from air sensor potentiometer to measure position of plate. This measurement determines engine load, which along with engine speed is used to control ignition timing. Potentiometer is connected to plate by air sensor lever.
Altitude Sensor (CIS-E III)
In direct relation to altitude or barometric pressure, altitude sensor sends a corresponding voltage signal to Fuel Injection Control Unit to correct air fuel mixture. Ignition Control Unit uses this signal to determine proper ignition timing. Altitude sensor is attached to ICU mounting bracket behind left kick panel.
Engine RPM Speed Sensor (CIS Digital Control)
An engine RPM speed sensor, located in upper part of bell housing, detects movement of ring gear teeth on flywheel. This signal is used to determine engine RPM and ignition timing.
Ignition Timing Reference Sensor (CIS Digital Control)
Sensor is located next to engine RPM speed sensor and detects rotation of a pin located 460 degrees BTDC. Sensor sends reference signal to control unit when TDC occurs for number one and number 4 cylinder.
The hall effect switch, located in ignition distributor, produces one signal for each revolution of the distributor. This signal occurs just before TDC of number one cylinder and is used to determine which signal from the ignition timing reference sensor is the actual TDC signal for number one cylinder. Do not rotate distributor to set base timing.
Knock Sensor
See DETONATION RETARD OPERATION under IGNITION SYSTEM in this article.
Oxygen Sensor
Oxygen (O2) sensor is heated type sensor which measures oxygen content of exhaust gases. Control unit uses data from O2 sensor to determine air fuel mixture. Sensor is positioned in exhaust system just ahead of catalytic converter (except CIS--E III system).
On CIS-E III system vehicles with manual transmission, O2 sensor is located on exhaust pipe just ahead of catalytic converter. On vehicles with automatic transmission, O2 sensor is located at front of catalytic converter.
Coolant Temperature Sensor (CIS Digital & CIS Motronic)
The coolant temperature sensor is located in the cylinder head coolant passage and informs ECU of engine operating temperature. Signal is used to provide corrections to air fuel mixture.
Coolant Temperature Sensor (CIS-E III)
Temperature sensor consists of 2 thermally variable resistors. One resistor signals temperature of coolant to ICU. The other resistor signals same information to FICU.
These signals are used to provide corrections to air fuel mixture, depending on coolant temperature. Both resistors have same resistance value. Temperature sensor is located in cylinder head coolant outlet flange.
Throttle Switches (CIS-E III)
Idle switch and full throttle switch provide throttle position data to both Fuel Injection Control Unit (FICU) and Ignition Control Unit (ICU). Throttle switches are located on throttle body.
Idle switch is closed when throttle plates are closed and opens when throttle opens approximately one degree. Idle switch signal determines operation of stabilizer valve, deceleration fuel shutoff and activation of a special ignition timing map.
Full throttle switch closes at about 10 degrees before full throttle. Full throttle switch signal determines full throttle enrichment and activation of a special timing map for full engine load.
ICU and FICU also use data from throttle switches to check operation of air sensor potentiometer.
Throttle Switches (CIS Motronic)
Idle switch and full throttle switch provide throttle position data to ECU. Throttle switches are located on throttle body. Idle switch is closed when throttle plates are closed and opens approximately one degree. Idle switch signal determines operation of idle stabilizer valve. Full throttle switch closes at about 10 degrees before full throttle. full throttle switch signal determines full throttle enrichment.
OUTPUT SIGNALS
Note. Each vehicle may be equipped with different combinations of computer controlled components. The following listed components may NOT be used on all models. For theory and operation on each output component, refer to the system indicated in brackets, to the right of each component.
- Canister Shutoff Solenoid (Emission Systems)
- "CHECK ENGINE" Light (Self-Diagnostic System)
- Denotation Sensor (Ignition System)
- Differential Pressure Regulator (Fuel Control)
- Idle Speed Control (Idle Control System)
- Ignition Coil (Ignition System)
- Ignition distributor (Ignition System)
Fuel Pump & Relay (Digital Control System)
The fuel pump assembly, located in fuel tank, is equipped with a pressure damper at the suction end. Fuel pump is activated during start-up and when engine is running. Fuel pump relay switches off fuel pump in absence of signal from ECU and provides voltage for cold start valve.
Fuel Pressure Regulator
Fuel pressure regulator functions to maintain a consistant pressure at the injectors.
Differential Pressure Regulator (CIS-E III)
Differential pressure regulator controls fuel flow in lower chamber of fuel distributor to assist in determining fuel mixture. A regulator designates zero Milliamps (mA) as a reference point. With vehicle at normal operating temperature and all engine controls functioning properly, regulator operates with current from Fuel Injection Control Unit (FICU) between +10 mA (rich) to -10 mA (lean).
When starter is operated, current to differential pressure regulator is increased to enrich fuel mixture. This will take place whenever engine is started and amount of increase will be regulated by coolant temperature. In extreme cold, current can be as high as 140 mA.
During cold acceleration, current can briefly raise to 6 mA to enrich fuel mixture. Enrichment is determined by engine speed and signals from temperature sensor.
During full load operation, full throttle switch closes, sending a signal to Ignition Control Unit (ICU). ICU sends a signal approximately 3 mA greater than signal that is currently present. This signal will vary, depending on engine speed and altitude.
When vehicle is decelerated, fuel to injectors is shut off by reversing current to -50 mA to -60 mA. Engine speed at which this reversing will take place is regulated by coolant temperature. Current will also be reversed if engine speed reaches 6600 RPM, acting as a governor. Differential pressure regulator is attached to fuel distributor. (Scheme 4)
Scheme 4
Idle Speed Control (CIS Digital)
Idle speed stabilizer is separate from digital control unit. The throttle switch is used to initiate idle speed control. The air control valve, located in throttle valve by-pass hose, receives signals from idle speed stabilizer.
With ignition on and engine off, air control valve is activated. This provides a valve opening which is determined by coolant temperture. After engine is started, idle stabilizer adjusts idle speed based on idle stabilizer thermo switch, throttle position and engine RPM. A/C operation will also send a signal to the ECU which will modify the signal to the air control valve. Engine speed is controlled by temperature from 1000 RPM at 0°F (-20°C) to a low of 720 RPM at 68°F (20°C).
Idle Speed Control (CIS-E III & CIS Motronic)
Idle stabiliztion system consists of rotary valve and return spring attached to an armature. Valve controls idle speed. Varying amounts of DC voltage sent by ECU causes motor to pull against return spring allowing air to by-pass throttle plate.
Idle speed is maintained between 650-790 RPM on warm engines and close to 1000 RPM on cold engines. No idle speed adjustments are necessary or possible. Idle stabilization valve is located between intake air boot and intake manifold.
Bosch Hall Effect Electronic Ignition
The Bosch Hall Effect electronic ignition system consists of an ignition coil, distributor with Hall Effect sending unit. Hall ignition control unit, vacuum and centrifugal advance mechanisms are present on some models.
The Hall Effect sending unit in the distributor receives voltage from the knock control unit or directly from the electronic ignition control unit. A trigger wheel (shutter blades), mounted on the distributor shaft passes in and out of the air gap of the Hall Effect sending unit, resulting in signal pulses. Some distributors employ one trigger wheel shutter/window for each engine cylinder; others use a single window to indicate cylinder No. 1 with additional sensors on the flywheel to indicate engine speed and TDC.
On models without timing/knock control units, vacuum and centrifugal advance mechanisms are used. Signals from the distributor Hall sending unit are sent back to the Hall control unit, which opens and closes the primary circuit to the ignition coil, firing the spark plugs.
On models utilizing a knock control unit, vacuum and centrifugal advance mechanisms are not used. The distributor Hall sending unit signal goes directly to the knock control unit which modifies the trigger signal to the ignition coil based on RPM, knock sensor input, and vacuum. On models with CIS-E models, throttle switch position signal is also used.
Ignition Coil
All systems employ an ignition coil equipped with side mounted power stage which switches primary current in coil on and off. This system is used in place of Hall Effect control unit. Power stage is controlled by signals from ECU.
Detonation Retard Operation (CIS Digital Control)
Knock sensor is mounted at center of left side of cylinder block. A 3-wire connectoer (Red) transmits signals to the ECU. The knock sensor signal will retard ignition timing in 3 steps of 2.6 degrees, up to a total of 7.8 degrees retard. When knocking stops, ECU will advance timing in steps of 1.3 degrees, back to the point knocking started.
Detonation Retard Operation (CIS-E III)
Knock sensor consists of piezoelectric crystal encased in a metal and plastic housing. Vibrations in engine cause crystal to generate small amounts of voltage. This voltage signal is used by Ignition Control Unit (ICU) to determine necessary timing retardation.
If knocking is detected, ICU will retard ignition 3.4 degrees. If knocking stops, timing will advance in steps of .54 degrees until it reaches pre-programmed value. If knocking continues, timing can be retarded as much as 12 degrees.
Knock sensor is located on left side of cylinder block, next to cylinder No. 3. Knock sensor connector is located on a bracket next to distributor.
Canister Shutoff Solenoid
Shutoff solenoid valve is de-energized when engine is truned off. This closes purge line between carbon canister and intake air boot, preventing fuel vapors which may cause hot start problem from collecting in intake tract.
When engine is started, canister shutoff solenoid is energized, allowing stored vapors to be purged from canister. Canister shutoff solenoid is located on top of carbon canister.
Evaporative Emissions System
System incorporates a charcoal canister which, during periods of vehicle non-operation, stores fumes produced through evaporation in the fuel tank and other related system components. During engine operation, fumes are purged from canister and consumed in the combustion process.
80 2.0L, 200 & 200 2.2L Turbo
The ECU will store faults for self-diagnosis. The ECU has a permanent fault code memory (50 states and Calif.), as well as a temporary fault code memory (Calif. only). When ECU detects a temporary fault, the "FAULT INDICATOR LIGHT" (FIL) on the instrument panel will flash. The FIL will continue to flash until ignition is turned off. The ECU may clear the fault on next engine start, and the FIL will not flash unless fault is detected again. Vehicle will have to be test driven for at least 5 minutes to reset fault. When ECU detects a permanent fault, FIL will flash but fault will remain in ECU memory until physically erased.
CIS-E III
Both the Fuel Injection Control Unit (FICU) and Ignition Control Unit (ICU) store faults for self-diagnosis. If a fault occurs, computer memory will store a code and corrective action will take place. For example, if coolant temperature sensor developes an open circuit, both control units will assume a calculation value of a fully warmed engine.
If ignition system is operating in a fully retarded position because of engine knock or a problem has developed in knock sensor system, indicator light will flash while driving.
California Models Only
All California vehicles are equipped with a "CHECK ENGINE" light located on the instrument panel. The light will illuminate when the ignition switch is turned to the "ON" position (bulb check) and when systems related to the emission controls are malfunctioning during normal operation with the engine running. For additional information, see SELF-DIAGNOSTICS article.