TURBOCHARGERS
On turbo models, a turbocharger and wastegate assembly are mounted on the exhaust manifold. At idle and light throttle, the turbo engine operates like a standard engine. When more power is required, exhaust gases spin the impeller and turbine. Exhaust flow and turbocharger RPM increase as engine RPM increases. As turbocharger RPM increases, boost pressure also increases.
The wastegate is the safety valve of the system, preventing excessive boost pressure which can cause engine damage. A signal from the Automatic Performance Control system energizes a solenoid which opens the wastegate to control optimum boost pressure. In the event of control system failure, the wastegate will open automatically to limit boost pressure.
Turbocharger operation requires a supply of clean oil. Engine oil pressure provides lubrication to the system.
COMPUTERIZED ENGINE CONTROLS
The computerized engine control system consists of 3 electronic control units (ECU's): a fuel injection ECU, an ignition ECU, and on turbo models, an automatic performance control (APC) ECU.
Fuel Injection ECU
The fuel injection system ECU receives and processes data from various sensors. It then sends signals to fuel injectors for correct fuel delivery under all operating conditions. The fuel injection ECU is located on the right kick panel on 900 Series; in engine compartment on left side of firewall on 9000 Series. This unit also controls the Automatic Idle Control (AIC) system.
Ignition ECU
The ignition ECU is located in the engine compartment, forward of the left front wheel housing on 900 Series. On 9000 Series, the ignition ECU is under the driver's seat. It receives inputs from a detonation sensor, fuel injection ECU and the Hall Effect sensor. From these inputs it calculates and controls ignition timing.
Automatic Performance Control (APC) ECU (Turbo)
The APC system ECU is located under the dash, left of the steering column. It receives signals from a detonation sensor, pressure sensor and ignition system ECU. The APC ECU processes these signals and sends a signal to a solenoid valve at the turbocharger to control optimum boost pressure.
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
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine the input device usage on a specific model, see appropriate wiring diagram in WIRING DIAGRAMS article in the ENGINE PERFORMANCE Section. The available input signals include the following
A/C Switch
When A/C switch is on, it sends a signal to the fuel injection ECU. The ECU sends a signal to the Automatic Idle Control (AIC) valve to increase idle speed to compensate for increased load.
Coolant Temperature Sensor
The coolant temperature sensor is located on the intake manifold flange. It transmits an engine temperature signal to the fuel injection ECU. If the ECU fails to receive this signal, it defaults to an assumed engine temperature of 113°F (45°C).
Detonation Sensor
This sensor is located in the engine block, below the intake manifold. When knocking occurs, it sends a signal to the ignition and APC ECU's.
EGR Temperature Sensor
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
Gear Selector Switch
Automatic transmission models are equipped with a switch that signals the fuel injection ECU whenever the transmission is in a range other than Park or Neutral. The ECU signals the Automatic Idle Control (AIC) valve to increase idle speed.
Hall Effect Sensor
This sensor transmits engine RPM and crankshaft position signals to the fuel injection, ignition and APC ECUs. On 900 Turbo it is located within the distributor. It is located on the crankshaft pulley on all others.
Mass Airflow Meter
This sensor measures mass airflow of air entering the engine intake system. It is located between the air cleaner and throttle body. After the engine is shut off, the fuel injection ECU sends a signal to the sensor filament to heat it for 4 seconds to burn off any deposits, provided that engine speed has been greater than 2000 RPM.
Oxygen Sensor
This sensor measures quantity of free oxygen in the exhaust gas. The fuel injection ECU uses a signal from this sensor to adjust fuel injection quantity. Sensor is threaded into the exhaust manifold.
Throttle Position Sensor
This sensor is located on the throttle body. It transmits throttle position to the fuel injection ECU.
Vehicle Speed Sensor
This sensor is located in the speedometer. It sends a signal to the fuel injection ECU to determine whether or not the vehicle is moving.
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.
Airflow Meter Self-Cleaning
See MASS AIRFLOW METER under INPUT DEVICES.
Automatic Idle Control Valve
See IDLE SPEED under FUEL SYSTEM.
Canister Purge Solenoid
See EVAPORATIVE EMISSIONS under EMISSION SYSTEMS.
CHECK ENGINE Light
See SELF-DIAGNOSTIC SYSTEM .
Cold Start Injector
See FUEL CONTROL under FUEL SYSTEM.
EGR Control Solenoid Valve
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Idle-Up Solenoid
See IDLE SPEED under FUEL SYSTEM.
Ignition Coil(s)
See IGNITION SYSTEMS .
Oxygen Sensor Heating Element
See FUEL CONTROL under FUEL SYSTEM.
Self-Diagnostics
See SELF-DIAGNOSTIC SYSTEM .
Wastegate Solenoid
See TURBOCHARGERS under AIR INDUCTION SYSTEM.
FUEL DELIVERY
The fuel system consists of a fuel tank, fuel pump, fuel lines, filter and a fuel pressure regulator. Fuel is supplied to each injector at a constant pressure.
Fuel Pressure Regulator
Fuel pressure regulator, located on fuel rail, maintains constant fuel pressure at fuel injectors. Excess fuel by-passes injectors and returns to fuel tank.
Fuel Pump
Fuel pump is located within the fuel tank. Fuel is strained through a mesh screen before entering the pump. A check valve, located on outlet side of pump, maintains pressure within the fuel system when engine is off.
Fuel pump relay supplies power to fuel pump. It is controlled by fuel injection ECU. Fuel pump relay is located on right kick panel on 900 Series, or behind glove box on 9000 Series.
On 900 Series, a signal from the fuel injection ECU opens a cold start injector to supply additional fuel under cold start conditions. This device is located at the throttle body.
The fuel injection ECU processes pulses from the ignition ECU to determine basic fuel injection timing. It also processes signals from other sensors for calculating pulse duration to control fuel injector on time.
Each fuel injector, located in the intake manifold, sprays atomized fuel directly toward the associated intake valve. All injectors are supplied with fuel from a common fuel manifold. Injection pulse duration is controlled by a signal from the fuel injection ECU. Injectors open simultaneously once per engine revolution, except during cold starting. During cold starting, injectors open twice per engine revolution.
The fuel injection ECU sends a signal to the to a heating element in the oxygen sensor. The function of the heating element is to bring the sensing element to operating temperature more quickly.
Automatic Idle Control (AIC) Valve
The automatic idle control valve consists of an air control valve and integral solenoid. This system provides a more stable idle speed during warm and cold engine operation. The fuel injection ECU sends a signal to the AIC valve to control the amount of air that by-passes the throttle valve.
On 900 Series, the fuel injection ECU sends a signal to an idle-up solenoid to increase idle speed when the air conditioner is on. This solenoid is located in the by-pass hose at the throttle body.
9000 Series
The DIS system is a capacitive discharge type. Components of the DIS include an ignition cartridge, Hall Effect sensor and knock detector. There is a separate coil for each spark plug. Energy for the spark is stored in a capacitor and discharged through the ignition coil based upon a signal from the ignition ECU.
When the engine is cranking, the ignition ECU establishes firing order by signals sent from the crankshaft sensor. During difficult start conditions (less than 420 RPM), a continuous series of sparks (multi-sparking) occurs during 70 degrees of engine rotation in the cylinder pair whose pistons are approaching TDC. Multi-sparking continues until engine speed reaches 850 RPM, and will reoccur if engine speed drops to less then 420 RPM. If the engine fails to start, multi-sparking will occur in all cylinders to remove spark plug electrode deposits.
900 Series
The ignition ECU receives a signal from the crankshaft position sensor. This signals is processed and sent to the ignition amplifier. The ignition amplifier sends a signal which opens the primary circuit of the ignition coil, thus generating a high voltage pulse which is directed to each spark plug by the distributor.
9000 Series With DIS
Ignition timing remains at base setting until engine speed reaches 850 RPM. At engine speeds greater than 850 RPM, the ignition ECU controls ignition timing. If the knock detector senses detonation, engine timing and boost pressure will be retarded. If detonation continues, the ignition ECU signals the fuel injectors to increase fuel delivery. No timing adjustment is possible on this system.
Ignition advance is controlled by the ignition ECU. Inputs from the fuel injection ECU, Hall Effect sensor, and coil are used by the ECU to calculate advance. A sensor detects any knocking in the engine and sends a signal to the ECU, which then retards ignition timing. On 900 Series Turbo, a pressure signal from the air intake duct controls a distributor-mounted diaphragm which retards timing.
AIR INJECTION
The pulse air injection system sends air to the exhaust manifold to reduce exhaust emissions (HC and CO). Components of the system include check valves, air injection manifolds, a nozzle by each exhaust valves and an air supply hose from the air cleaner. Filtered air from the air cleaner flows through the pulse air valves by means of exhaust manifold pressure variation. Check valves prevent exhaust gases from flowing back into the air cleaner.
CATALYTIC CONVERTER
All vehicles are equipped with a 3-way catalytic converter. This device frees oxygen from oxides of nitrogen, and oxidizes hydrocarbons and carbon monoxide.
EVAPORATIVE EMISSIONS
Fumes from the fuel tank are stored in a charcoal canister while the vehicle is not running. When the engine is started, intake manifold vacuum purges these fumes through a canister purge solenoid, based upon a signal from the ECU. The canister is located in the left front of the engine compartment on 900 Series; in the right front wheel housing on 9000 Series.
A rollover valve in the fuel evaporation line closes if the vehicle rolls over. It is located in the evaporation line, above the fuel tank. A vacuum relief valve in the fuel filler cap bleeds air into the fuel tank if the vent lines become plugged.
EXHAUST GAS RECIRCULATION (EGR)
To lower oxides of nitrogen (NOx) exhaust gas emissions, a computer controlled exhaust gas recirculation system is used. Depending on engine operating temperature, the fuel injection ECU controls an EGR solenoid to control vacuum signal to EGR valve. Valve routes exhaust gases from the exhaust manifold into the intake manifold.
An EGR temperature sensor is used on some models. Sensor informs fuel injection ECU when EGR function is occurring. This enables ECU to determine if system is functioning as commanded.
POSITIVE CRANKCASE VENTILATION
All vehicles have a completely closed crankcase ventilation system. Crankcase fumes are drawn into the intake manifold by manifold vacuum. When intake manifold vacuum is low, the fumes are diverted into the intake air duct ahead of the throttle body and turbocharger (if equipped).
All vehicles are equipped with a CHECK ENGINE light on the instrument panel. The light will come on when the ignition switch is turned to the ON position (bulb check), and when emission controls malfunction during normal operation. For additional information, see G - TESTS W/ CODES article in the ENGINE PERFORMANCE Section.
MISCELLANEOUS CONTROLS
Note. Although not considered true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
A/C CLUTCH
At full throttle, the fuel injection ECU opens the ground circuit to the A/C clutch to inhibit A/C operation.
Cooling Fan Motor
The cooling fan is controlled by a temperature switch on the left side of the radiator. Failure of the fan to operate may result in overheating and detonation.
Cooling Fan Control Relay
The cooling fan relay is located in the power distribution box, on the left rear of the engine compartment. When the temperature switch closes, it grounds the relay coil. When the relay is energized, it supplies battery voltage to the fan motor. A signal from an A/C (if equipped) pressure switch also energizes the relay.