INTRODUCTION
This article covers the basic description and operation of engine performance related systems and components. Prior to diagnosing vehicles or systems with which you are not completely familiar, read through this article.
AIR INDUCTION SYSTEM
Air drawn in through air cleaner passes through air mass meter to turbo compressor unit (if equipped). Compressed air flows through intercooler, which cools incoming air charge, passing through throttle valve to intake manifold.
To smooth out induction system pulsations when throttle is closed rapidly, a vacuum operated relief valve is mounted on the side of the turbo unit to provide an additional path for incoming air, by-passing intercooler.
TURBOCHARGERS
Turbo equipped models use a water-cooled turbocharger, mounted directly to the exhaust manifold with a wastegate assembly attached to rear of turbine housing. The turbocharger consists of a turbine/compressor assembly, oil supply system and wastegate. Other components include impellers, impeller shaft, bearings and impeller housings.
At idle and light throttle, the Turbo engine operates like a standard engine. When more 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.
The safety valve of the system is a pressure actuated wastegate that prevents excessive intake boost pressure. If boost pressure exceeds safe limits, engine damage may result. The wastegate opens when exhaust pressure exceeds a predetermined limit and allows exhaust gases to by-pass compressor.
Additional engine protection is provided by the Automatic Performance Control (APC) system. The APC system senses engine knock and automatically cuts back the amount of boost.
Turbocharger operation requires a large quantity of clean oil to prevent bearing failure. Engine oil pressure provides constant lubrication to the system.
Automatic Performance Control (APC) System
APC system is used on Turbo models only. System consists of knock sensor, intake pressure sensor, APC system Electronic Control Unit (ECU) and wastegate solenoid valve. System monitors engine knock and varies manifold pressure applied to boost wastegate through solenoid valve. By controlling pressure at which wastegate opens, system can limit maximum boost to avoid engine damage.
- Intake Pressure Sensor Located under left side of instrument panel, on bracket. Intake pressure sensor vacuum sourced at port on manifold side of throttle valve.
- Wastegate Solenoid Valve Located on bracket near radiator fan shroud. Switches intake manifold pressure to wastegate to control turbo boost pressure.
COMPUTERIZED ENGINE CONTROLS
The 900S, 9000S and all Turbo models are equipped with the Bosch LH Jetronic system. LH Jetronic uses an air mass meter to determine air density, altitude, and temperature. These measurements are then sent to the fuel injection system ECU.
The Bosch LH-Jetronic fuel injection system integrates the fuel injection and idle speed control functions into one system. Fuel injection system Electronic Control Unit (ECU) controls system functions.
The LH-Jetronic fuel injection system operates with moderate fuel pressure, held constant by a line pressure regulator. Fuel is metered into the cylinders by electrically controlled solenoid valves in the injectors. The injectors are installed just ahead of each cylinder intake valve.
Actual duration of injection (2-12 milliseconds), is determined by the ECU. The ECU receives several signals on various driving, engine and outside conditions from a set of sensors and an air mass meter. Signals from air mass meter and exhaust gas oxygen sensor provide most of the information used by the ECU to maintain proper air/fuel ratios. An idle speed adjustment screw is located on throttle housing.
Fuel Injection ECU
The Bosch LH-Jetronic fuel injection system ECU is a microprocessor based computer that receives and evaluates readings from various sensors. The ECU then produces a signal that is sent to each injector to ensure the correct amount of fuel delivery for all operating conditions. Located in the right kick panel, ECU also controls the Automatic Idle Control (AIC) system.
Automatic Performance Control (APC) ECU
APC system ECU (Turbo only) is located under dash, to the left of steering column, behind knee shield. ECU receives electric signals from detonation sensor, intake pressure sensor and engine speed information from ignition system. ECU uses these signals to calculate optimum boost pressure which is obtained through ECU controlled activation of the APC solenoid valve.
EZK Ignition ECU
Ignition ECU is located under dash, to the left of steering column, behind knee shield. ECU receives input from detonation sensor, fuel injection ECU (engine load) and engine RPM (monitored at Hall sensor). ECU uses these inputs to calculate and control ignition timing.
Note. For ease of understanding, components will be grouped into 2 categories. The first category, INPUT DEVICES , are 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
A/C Switch
When A/C switch is on, ECU receives voltage signal to energize A/C relay. A/C relay has a momentary delay to allow ECU to signal Automatic Idle Control (AIC) valve to increase idle speed to compensate for increased load.
Air Mass Meter
The air mass meter continually measures temperature, amount, density, and speed of air entering engine intake system. The meter consists of a platinum wire filament located within intake air stream, and a circuit board with a CO adjustment potentiometer.
The wire filament is kept at 212°F (100°C) above the temperature of air entering engine regardless of composition of air entering engine. The air mass meter sends a temperature related signal to the circuit board for processing. Once processed, airflow signal is sent to injection ECU.
When engine is turned off, dirt build-up is burned off wire element by heating filament to approximately 1920°F (1050°C) for one second, 4 seconds after engine is off. The injection ECU then de-energizes air mass meter relay once burn-off cycle is complete.
Coolant Temperature Sensor
The coolant temperature sensor is located in the cylinder head or engine block. This sensor provides ECU with an engine temperature signal. If signal from temperature sensor is not reaching ECU, an engine temperature of 113°F (45°C) will be assumed by ECU.
If sensor reads a high engine temperature (with cooling system operating properly), this would indicate combustion temperature that is too high. The ECU would then enrichen the mixture (to the point allowed by the oxygen sensor and air mass meter signals) to lower combustion and engine temperature.
Detonation Sensor (Ignition & APC System)
Located on engine block, below intake manifold, detonation sensor converts knocking vibration into an electrical signal. Signal is transmitted to ECU (ignition and APC units) where it is compared against stored information. Ignition ECU readajusts the timing to eliminate detonation. APC unit adjusts turbo boost pressure through APC solenoid valve to eliminate detonation.
Engine Speed
The engine speed signal is generated by an electronic (Hall Effect) ignition sensor. The low voltage ignition primary pulses are monitored at low tension side of ignition coil. Injection timing is regulated by this signal. Also used as input to APC and AIC systems.
Gear Selector Switch
Automatic transmission models are equipped with a selector position switch that signals ECU when transmission is shifted into "Drive". ECU signals automatic idle control valve to increase idle speed by 50 RPM.
Hall Effect Sensor
Sensor consists of a semiconductor element and magnet. Magnet acts on semiconductor to create a magnetic field. A slotted rotor alternately interrupts magnetic field. Pulse from sensor is amplified and sent to ignition coil where it is used as tachometer (RPM) signal and monitored by the ECU.
Oxygen Sensor
The oxygen sensor checks exhaust gas for presence of unburned oxygen. Unburned oxygen in exhaust gas indicates incomplete combustion due to improper mixture, spark timing or other conditions. Oxygen sensor has preheating function to bring sensor to operating temperature quickly.
Throttle Switch
The throttle valve switch consists of double microswitch. The throttle switch consists of built-in contacts which are opened and closed by a throttle cam. One switch is activated at idle and the other during wide open throttle conditions. The switch is located on the side of throttle housing.
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.
- A/C Relay (Idle Speed)
- Air Mass Meter Self-Cleaning (Hot-Wire Input Devices)
- Automatic Idle Control Valve (Idle Speed)
- "CHECK ENGINE" Light (Self-Diagnostic System)
- Fuel Pump Control (Fuel Delivery)
- Fuel Injectors (Fuel Control)
- Fuel Pressure Regulator (Fuel Delivery)
- Evaporative Loss Control Device (Emission Systems)
- Exhaust Gas Sensor Heater Control (Emission Systems)
- Self-Diagnostics (Self-Diagnostic System)
- Wastegate Solenoid (Air Induction Systems)
FUEL DELIVERY
The fuel system consists of fuel tank, ejector or supply fuel pump, main fuel pump, fuel lines, filter, and a line pressure regulator. Fuel is supplied to each injector at a constant pressure. Only fuel injection duration is varied, meeting changing engine requirements.
Fuel Pressure Regulator
Fuel pressure regulator is fitted to end of fuel rail. Regulator maintains a constant fuel pressure at injectors by a spring operated diaphragm and valve. Excess fuel by-passes injectors and returns to fuel tank.
Fuel Pump
The fuel pump is an in-tank electrically operated vane pump. Fuel pump assembly consists of a main fuel pump, a pressurized container and an ejector or supply fuel pump. Ejector pump is driven by fuel returning to tank.
Fuel is strained through a mesh screen before entering fuel pump. There is a check valve on outlet side of pump to prevent fuel supply from draining back into tank.
Fuel Pump Relay
The fuel pump relay supplies power to the fuel pump. It is controlled by the ECU. When the ECU supplies power to the coil side of the relay, the circuit closes, allowing current to flow to the fuel pump.
Injectors
The injectors, located in intake manifold, point directly toward intake valve. All injectors are supplied with fuel from a common fuel manifold. The injection pulse is controlled electrically by a needle valve in lower section of injector. The needle valve is operated by an electric solenoid which is switched on and off by the ECU.
ECU controls timing and duration of injector operation based on input signals from Hall sensor, throttle sensor, temperature sensor and air mass meter. ECU uses pre-programmed values to calculate optimum injector duration.
Injectors open simultaneously once per engine revolution, except during cold starting. During cold starting, injectors are opened twice per engine revolution.
Automatic Idling Control (AIC)
The idle control system consists of an air control valve and solenoid. This system is used to provide a more stable idle speed during warm and cold engine operation.
This system determines the volume of air that by-passes throttle valve. Airflow volume is determined by size of opening in valve. When airflow drops below a specified volume, the ECU signals the AIC system to modify size of valve opening.
A/C Relay
A/C relay signals ECU when A/C compressor is to be turned on. This allows ECU to signal AIC system to raise idle RPM.
IGNITION SYSTEM
All models are equipped with Bosch Hall Effect or Bosch EZK electronic ignition system. In the event of internal distributor failure, the distributor must be replaced as a unit.
HALL EFFECT
Hall Effect sensor energizes ignition amplifier, closing primary circuit and charging ignition coil. Pulse from sensor is amplified and sent to ignition coil where it is used as tachometer (RPM) signal and monitored by the ECU. The ECU transmits signals to the ignition system which opens the primary circuit of the coil and triggers ignition spark.
BOSCH EZK
Same operation and components as Hall Effect type except, EZK ignition is equipped with feedback detonation control system.
ELECTRONIC IGNITION SYSTEM (DISTRIBUTOR TYPE)
The ECU receives signals from the fuel injection ECU, knock sensor (if equipped) and crankshaft mounted Hall sensor. Signals are analyzed and compared with information in memory. ECU determines timing.
ECU signals ignition system to fire spark plug. Distributor rotor passes high voltage from coil to appropriate spark plug.
Ignition Timing Advance Control
Ignition advance is controlled by the ECU. Inputs from fuel injection ECU (barometric), Hall sensor (ignition pulses), and coil (RPM) are used by ECU to determine correct advance. ECU then resets ignition timing by transmitting signals to ignition system which opens primary circuit and triggers spark.
Detonation Retard Operation
A detonation sensor detects any knocking in the engine and applies a signal to the ECU which then automatically retards ignition timing in accordance with programmed parameters and engine load and speed input signals received.
The knocking related ignition timing is controlled on individual cylinders. The ignition timing may vary from one cylinder to the next. However, load related timing is controlled for all cylinders together.
PULSE AIR SYSTEM
The pulse air induction system is designed to send air to exhaust manifold to reduce exhaust emissions (HC and CO). System consists of: 2 check valves, 2 air injection manifolds, 4 nozzles (at exhaust valves) and air supply hose (from air cleaner).
Fresh air from air cleaner is drawn through pulse air valves by exhaust manifold pressure variation. In exhaust manifold air is used for oxidation of exhaust gases to reduce emissions. Check valves prevent exhaust gases from flowing back into air cleaner.
EXHAUST GAS RECIRCULATION (EGR) CONTROL
The Exhaust Gas Recirculation (EGR) system is used to help control formation of NOx emissions. Recirculating a limited amount of exhaust gas into the intake system lowers combustion temperatures causing reduction in NOx emissions. Thermostatic valve is used to control EGR operation pertaining to engine temperature.
On-Off EGR System (Turbo)
Exhaust gases are routed through the No. 2 cylinder head port to EGR valve. Opening of EGR valve is regulated by a vacuum port in throttle valve housing. At idle, vacuum is not applied and EGR remains closed.
The EGR system opens when engine speed reaches 1900 RPM. Special size orifice is used for controlling amount of recirculated exhaust gas. The EGR operation is prevented by the thermostatic switch when engine temperature is below 110°F (43°C).
Two-Port EGR System (Non-Turbo)
Routing of TWO-PORT EGR system is similiar to the ON-OFF EGR system except that orifice is not used. Amount of recirculated exhaust gas is controlled by a variable opening in the EGR valve.
Opening of EGR valve is regulated by 2 adjacent vacuum ports in throttle valve housing. At idle, vacuum is not applied to either port, resulting in a closed system.
At off-idle or low speed, vacuum is applied to one port only, allowing partial opening of EGR valve. When throttle valve opens past the second port, full vacuum is applied to both ports. This allows full exhaust gas recirculation through EGR valve. Thermostatic valve prevents EGR operation when engine temperature is below 110°F (43°C).
Proportional EGR System (Turbo)
Proportional EGR system is operated by vacuum and pressure. Hoses are connected upstream of throttle valve and to thermostatic valve. Thermostatic valve prevents EGR operation when engine temperature is below 68°F (20°C) on 900 models and 86°F (30°C) on 9000 models.
Signal converter is used to control EGR valve due to engine load. During idle, both vacuum and pressure connections are upstream of throttle valve. Pressure differential remains the same which allows EGR valve to remain closed.
On partial load application, throttle valve is partially open and turbocharger is charging. Pressure differential on each side of throttle valve will open EGR valve. On full load, pressure signal is approximately equal causing EGR valve to remain closed.
On low load, pressure connection on rear of throttle valve supplies vacuum to signal converter. Signal converter operates allowing EGR to open.
EVAPORATIVE EMISSIONS SYSTEM
The fuel evaporation system is designed to prevent fuel vapor from reaching the atmosphere. System includes a plastic fuel tank, vacuum relief filler cap, rollover valve, check valve, charcoal canister, and connecting lines and hoses.
When engine is stopped, fuel vapor from fuel tank flows through vapor line into charcoal canister where it is stored. When engine is running, a vacuum signal from throttle body acts on check valve, opening port at inlet manifold. Fresh air is drawn through charcoal canister as manifold vacuum pulls stored fuel vapor into combustion chambers for burning. The check valve regulates amount of vapor flow.
A rollover valve in fuel evaporation line shuts off line if vehicle turns over. It is located in-line, above fuel tank. Vacuum relief fuel filler cap lets air into fuel tank if vent lines become plugged. This prevents tank collapse or engine fuel starvation.
INTEGRATED FAULT DIAGNOSIS SYSTEM
Fuel injection ECU system (LH 2.4) is equipped with self-diagnostic system that makes fault diagnosis easier and more accurate by displaying error codes. Error codes are indicated by flashes of the "CHECK ENGINE" light. Reference can then be made to error code tables where location of fault can be narrowed down or pinpointed.
Fuel Injection System LH 2.4
Vehicles are equipped with a "CHECK ENGINE" light located on the main instrument panel (Not connected with "CHECK ENGINE" light on EDU 2 trip computer). 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 (Mode 1) with the engine running. For additonal information, see TESTS W/CODES article.
See also:
• WIRING DIAGRAMS
• TESTS W/CODES
• INPUT DEVICES
• OUTPUT SIGNALS