VARIABLE AIR INDUCTION SYSTEM (3.0L)
The variable air induction system used on 3.0L engine changes intake manifold geometry to maximize engine performance throughout entire engine speed range. This variable geometry is achieved by the computer-controlled induction valve control solenoid that controls the movement of the induction valve.
COMPUTERIZED ENGINE CONTROLS
Fuel is metered to intake system through individual injectors (one for each cylinder), mounted in intake manifold next to intake valves. Powertrain Control Module (PCM) monitors data from various sensors and controls such functions as fuel injector pulse width ("on" time), ignition timing and emission control devices.
POWERTRAIN CONTROL MODULE (PCM)
If a system malfunction occurs, a back-up system within PCM controls fuel and ignition system functions according to preprogrammed values (limp-in mode). This allows vehicle to be driven, but performance may not be optimal. A self-diagnostic function allows PCM to store Diagnostic Trouble Codes (DTCs) in its memory. If a system fault occurs, Malfunction Indicator Light (MIL) will illuminate to inform driver of system problems and the appropriate DTC will be stored in memory. For further self-diagnostic system information, see appropriate SELF-DIAGNOSTICS article. PCM is located under right side of dash, behind glove box on all other models.
Note. Components are grouped into 2 categories. First category is INPUT DEVICES , which are components that control or produce signals monitored by PCM. Second category is OUTPUT SIGNALS , which are components controlled by PCM.
INPUT DEVICES
Vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input usage on a specific model, see WIRING DIAGRAMS article. Available input signals include the following
A/C Switch
Signals PCM of A/C operation.
Atmospheric Pressure Sensor
Detects amount of intake air by measuring the atmospheric conditions. PCM uses this signal to compensate for variations in altitude, which affect air/fuel mixture ratios.
Blower Motor Switch
Signals PCM of blower motor operation.
Camshaft Position (CMP) Sensor
Sensor is located on camshaft support on left cylinder bank. Based on signals received from CMP sensor, PCM identifies cylinder No. 1. PCM then uses these signals to trigger ignition system and fuel injectors.
Crankshaft Position (CKP) Sensor
Sensor is located on oil pump, at front center of cylinder block. Based on signals received from CKP sensor, PCM determines crankshaft angle and triggers ignition system and fuel injectors.
Engine Coolant Temperature (ECT) Sensor
PCM supplies reference voltage signal to thermistor. Resistance of ECT sensor changes with variations in coolant temperature, causing signal voltage to increase or decrease.
Front & Rear Heated Oxygen Sensors (HO2S)
Sensors generate voltage according to exhaust gas oxygen content. Signal voltage increases when oxygen content is low (rich), and decreases when oxygen content is high (lean). PCM controls air/fuel ratio based on voltage generated.
Fuel Level Sensor
Monitors fuel level in the fuel tank.
Fuel Tank Pressure Sensor
Detects evaporation gas pressure in fuel tank.
Fuel Temperature Sensor
Monitors temperature of fuel in fuel tank.
Ignition Switch
Signals PCM of ignition switch operation.
Intake Air Temperature (IAT) Sensor
PCM applies reference voltage to a thermistor installed on air cleaner housing. Signal voltage increases and decreases with variations in air temperature.
Intake Air Temperature (IAT) & Pressure Sensor
This device integrates the IAT sensor and pressure sensor in one unit that is mounted on the intake manifold. This device provides the PCM with temperature and pressure of incoming air.
Intake Manifold Pressure Sensor
PCM applies reference voltage to sensor on throttle body. Signal voltage increases and decreases with variations in manifold absolute pressure.
Knock Sensor (KS)
Knock sensor is installed on cylinder block (two used on 3.0L) to detect cylinder block vibrations resulting from detonation. If detonation occurs, KS generates a signal to PCM. Using this signal, PCM retards spark timing until detonation stops. This device may also be referred to as a detonation sensor.
Neutral Position Switch
Switch sends manual transaxle neutral gear position signal to PCM.
Park/Neutral Position (PNP) Switch
Switch sends automatic transaxle gear position signal to PCM.
Power Steering Pressure Switch
Switch sends power steering pressure signal to PCM.
Pressure Sensor
Provides information on incoming air pressure.
Rear Defogger Switch
Signals PCM of rear defogger operation.
Starter Switch
Signals PCM of engine cranking condition.
Throttle Position (TP) Sensor
TP sensor is a potentiometer. TP sensor sends PCM a signal corresponding to throttle valve position. PCM uses these signals to control air/fuel ratio during acceleration, deceleration and idle.
Vehicle Speed Sensor (VSS)
VSS is a pick-up type output sensor mounted on the transaxle. VSS generates a 4-pulse signal (16-pulse on automatic transaxle) for every rotation of the front differential. On automatic transaxle, VSS signal is sent to transaxle control module where it is converted to a 4-pulse signal and sent on to the PCM and speedometer. On manual transaxle, VSS signal is sent directly to PCM and speedometer.
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 of each output component, refer to indicated system.
Canister Purge Control Valve (CPCV)
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Data Link Connector (DLC)
See SELF-DIAGNOSTIC SYSTEM .
EGR Solenoid
See EXHAUST GAS RECIRCULATION (EGR) under EMISSION SYSTEMS.
Fuel Injector(s)
See FUEL CONTROL (SFI) under FUEL SYSTEM.
Fuel Pump Relay
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Tank Pressure Control Solenoid Valve
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Idle Air Control (IAC) Solenoid Valve
See IDLE SPEED under FUEL SYSTEM.
Ignition Coil
See IGNITION SYSTEMS .
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
Purge Control Solenoid (PCS) Valve
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Self-Diagnostics
See SELF-DIAGNOSTIC SYSTEM .
Tachometer
See TACHOMETER under MISCELLANEOUS CONTROLS.
See VARIABLE AIR INDUCTION SYSTEM (3.0L) under AIR INDUCTION SYSTEMS.
Vent Control Solenoid Valve (VCSV)
See FUEL EVAPORATIVE SYSTEM under EMISSION SYSTEMS.
Fuel Pressure Regulator
Fuel pressure regulator maintains constant fuel system pressure by bleeding excess fuel at injector rail back to fuel tank. Intake manifold vacuum acts on regulator diaphragm to control position of bleed-off valve in regulator.
Fuel Pump
Impeller-type pump is used. Fuel pump is located in fuel tank. Fuel pump pressurizes fuel through in-line filter to fuel rail. Fuel pump receives battery power through fuel pump relay.
PCM energizes fuel pump relay based on inputs from ignition switch and ignition coil. During cranking, cranking circuit supplies current to energize fuel pump relay. After engine starts and key is released to RUN position, PCM provides fuel pump relay ground. This activates fuel pump.
Fuel Injectors
Fuel is supplied to engine through injectors located near intake valve ports. PCM controls injector pulse width, which controls quantity of fuel metered through injectors.
Injectors are pulsed sequentially in spark plug firing order. Constant fuel pressure is maintained to the injectors. Air/fuel mixture is regulated by amount of time injector stays open (pulse width). Various sensors provide information to the PCM to control pulse width.
The IAC solenoid valve is incorporated in throttle body and regulates amount of air which by-passes throttle valve built into throttle body. It is activated by signals sent by PCM to maintain engine idle speed to specified engine speed.
Idle air control solenoid valve is a "current-proportion" solenoid type which consists of a coil, valve shaft, spring and housing. Housing is integral part of throttle body and is provided with an air passage opened or closed by valve.
DISTRIBUTORLESS IGNITION
Note. Coil-on-plug technology is used on 3.0L. PCM directly controls power transistor to control ignition timing.
Distributorless ignition system (DIS) is controlled by PCM. PCM receives signals from engine coolant temperature sensor, crankshaft position sensor, camshaft position sensor, knock sensor, throttle position sensor and park/neutral position switch to operate engine at optimum efficiency. Ignition timing is also determined by PCM which immediately transmits a primary current off signal to the power transistor to control ignition timing. Ignition timing is fixed during starting.
Ignition Timing Advance Control
On all models, ignition timing advance is controlled by PCM. Based on sensor input signals, PCM adjusts ignition timing to preprogrammed advance and retard specifications.
When engine knock occurs, the KS generates a signal to PCM. PCM retards spark timing until engine knocking stops, then gradually advances spark timing.
AIR ASSIST INJECTOR
This component meters air directed to base of injectors. The air is mixed with the fuel to improve fuel atomization at idle speeds only.
EXHAUST GAS RECIRCULATION (EGR)
EGR lowers oxides of nitrogen (NOx) exhaust emissions by admitting exhaust gases back into intake system. Exhaust gases lower peak combustion temperatures, which lowers NOx emissions.
This system consists of EGR valve, EGR solenoid and backpressure transducer (BPT). EGR valve, located between exhaust manifold and collector, is controlled by vacuum through BPT from throttle body and controls exhaust gas flow from exhaust manifold to intake manifold.
EGR solenoid, located between throttle body and EGR valve, is controlled by PCM according to engine driving conditions, and opens and closes the vacuum line between BPT and EGR valve diaphragm.
BPT, located between throttle body and EGR solenoid valve, varies throttle port vacuum operating EGR valve according to throttle opening and exhaust gas pressure, and controls rate of exhaust flow to EGR valve.
Located on top of canister, this vacuum-controlled valve opens and closes purge line between intake manifold and canister. CPCV valve remains closed at idle because ported vacuum activates its control diaphragm. When vacuum activates control diaphragm, purge line opens, and stored vapors are drawn into intake manifold.
Fuel Cut Valve (FCV)
On AWD models, fuel cut valve is built onto evaporation pipe of fuel tank. Rising level of fuel in fuel tank causes a float to move up and close the cap hole to prevent fuel from entering evaporation line.
Fuel Tank Pressure Control Solenoid Valve (FTPCSV)
This valve is located in evaporative emission hose between shut valve on fuel filler pipe and evaporative canister. When internal pressure inside fuel tank becomes greater than atmospheric pressure, ECM opens valve to allow evaporative emissions into evaporative canister. When internal pressure inside fuel tank becomes less than atmospheric pressure, ECM opens valve to allow fresh air into system. ECM closes valve during evaporative emission diagnosis.
Purge Control Solenoid (PCS) valve, located in evaporation line between canister and ported vacuum source, is built into collector chamber. See CANISTER PURGE CONTROL VALVE (CPCV) . Under appropriate conditions, PCM energizes PCS valve. This allows ported vacuum signal to CPCV.
Rollover Valve
Rollover valve is incorporated into the fuel system for prevention of fuel leakage in the event of vehicle rolling over. Valve will cut fuel flow if vehicle is rolled 90 degrees or more.
Vent control solenoid valve, located at intake port of canister, is normally open to atmosphere. PCM sends a signal to VCSV to close the port to air when evaporation gas is detected at evaporation line.
POSITIVE CRANKCASE VENTILATION (PCV)
PCV system is designed to prevent blow-by gases in engine crankcase from escaping into atmosphere. System consists of a sealed oil filler cap, valve cover with fresh air inlet, connecting hoses, air inlet duct and PCV valve.
PCV valve contains a spring-loaded plunger. By opening and closing in direct relation to engine load, PCV valve meters blow-by gas flow to combustion chamber. During periods of high manifold vacuum, such as at idle or deceleration, valve is almost completely closed, limiting flow of blow-by gases. During cruise speeds, valve permits a greater flow of blow-by gases.
Under conditions in which high amounts of crankcase pressure are produced (such as heavy loads or at wide open throttle), system allows excess blow-by gas back through air intake duct.
Self-diagnostic system monitors output signals through DLC. Diagnostic Trouble Codes (DTCs) can only be read using a scan tool connected to DLC. For additional information, see SELF-DIAGNOSTICS article.
All vehicles are equipped with MIL (CHECK ENGINE light) on instrument panel. Light comes on when ignition switch is turned on (bulb check), and when system malfunctions occur. For additional information, see SELF-DIAGNOSTICS article.
PCM provides signal to drive tachometer.