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.
INTAKE AIR BY-PASS (IAB) CONTROL SYSTEM
Note. Intake Air By-Pass (IAB) control system is only used on GS-R models.
The intake manifold provides 2 intake air paths: long and short. Increased engine torque over a broad range is achieved by using IAB control valves to switch between intake air paths. High torque at low RPM is achieved by using long intake air path only. High torque at higher RPM is achieved by using both intake paths.
System Operation
When engine RPM is less than 5750 RPM, a signal from ECM energizes IAB control solenoid valve. Intake air is directed through smaller intake air path. When engine speed is more than 5750 RPM, IAB solenoid valve is deactivated by ECM.
When IAB solenoid is deactivated, vacuum is cut to IAB control diaphragm causing spring loaded IAB control valves inside intake manifold to open. When IAB control valves open, intake air goes through short intake path, reducing airflow resistance and increasing engine torque. A malfunction in IAB control system will cause a low engine power condition.
VARIABLE VALVE TIMING & LIFT ELECTRONIC CONTROL SYSTEM (VTEC)
Note. VTEC rocker arms are used for both intake and exhaust valves.
VTEC uses 3 different camshaft lobes and rocker arms, synchronizer pistons, and a VTEC solenoid valve. (Scheme 1) The 2 low lift cam lobes operate primary and secondary (outer) rocker arms. The high lift cam lobe operates the connecting (middle) rocker arm. The PCM controls VTEC solenoid valve which in turn operates synchronizer pistons. (Scheme 1)
At low speed, primary and secondary rocker arms control valve timing, lift, and duration. The connecting (middle) rocker arm remains disengaged, and has no effect on engine operation. At high RPM with heavy engine load, PCM activates VTEC solenoid valve to apply oil pressure to synchronizer pistons located in primary and secondary rocker arms. This locks primary, connecting, and secondary rocker arms together so they are driven as a single unit by high lift cam lobe which the connecting rocker rides on.
Scheme 1
POWERTRAIN CONTROL MODULE (PCM)
Note. The Powertrain Control Module (PCM) may be referred to as Engine Control Module (ECM).
The PCM controls fuel injector timing and duration, idle speed, ignition timing, PCM back-up functions, and other functions. The PCM is located in front passenger footwell area. Remove passenger side kick panel to expose PCM.
Note. Components are grouped into 2 categories. The first category is INPUT DEVICES, which are components that control or produce signals monitored and processed by the PCM. The second category is OUTPUT SIGNALS , which are components controlled by the PCM.
INPUT DEVICES
These vehicles are equipped with different combinations of input devices. Not all devices are used on all models. To determine input device usage on a specific model, see appropriate wiring diagram in the WIRING DIAGRAMS article.
A/C Pressure Switch
Signals PCM when A/C is on. PCM uses this input to control Idle Air Control (IAC) valve and adjust engine idle to compensate for extra engine load.
A/T Gear Position Signal
Informs the PCM when automatic transmission is in Neutral or Park.
Alternator FR (ALT FR) Signal
ALT FR signal is used by PCM to control alternator output in accordance with electrical load and driving conditions. This ensures optimum engine load and increased fuel economy.
Barometric Pressure (BARO) Sensor
Converts atmospheric pressure into electrical signals. Barometric pressure sensor is inside PCM.
Battery Voltage (IGN 1)
When ignition is on, a battery voltage signal (ignition circuit) is sent to the PCM.
Brake Switch Signal
Signals the PCM that the brake pedal has been pressed. The PCM uses this input signal to control idle speed.
Crankshaft Speed Fluctuation (CKF) Sensor
A pulse signal with which PCM can detect minute changes in crankshaft speed. Is used to detect misfires.
Crankshaft Position (CKP) Sensor
Sensor detects speed and position of crankshaft. Used for fuel injection timing and ignition timing.
Cylinder Position (CYP) Sensor
Detects when piston in No. 1 cylinder is at TDC on compression stroke. Used to maintain sequential injection.
Engine Coolant Temperature (ECT) Sensor
This sensor is a thermistor which sends a signal to PCM proportional to engine coolant temperature. PCM uses this input to control air/fuel mixture, timing, and idle speed.
EGR Valve Lift Sensor
EGR valve lift sensor signals PCM how much EGR valve lift there is during engine operation. See EGR VALVE LIFT SENSOR under EMISSION SYSTEMS.
Electrical Load Detection (ELD)
Electrical load signal to PCM. Used for alternator control and idle speed adjustment.
Intake Air Temperature (IAT) Sensor
IAT sensor is a thermistor which determines intake air temperature. IAT sensor resistance decreases as intake air temperature increases. PCM uses the signal from this sensor to control air/fuel mixture.
Knock Sensor (KS)
Piezo-electric sensor creates small current when detecting a detonation. When knock sensor detects detonation, PCM will retard ignition timing.
Mass Airflow (MAF) Sensor
MAF sensor converts intake air temperature and intake air flow into an air mass value. Air mass value is converted to an electrical signal which is sent to PCM. PCM uses this input to control air/fuel mixture.
Manifold Absolute Pressure (MAP) Sensor
MAP sensor converts absolute pressure (vacuum) into an electrical input signal. PCM uses this input signal to control air/fuel mixture.
Power Steering Pressure (PSP) Switch Signal
PSP switch signals PCM of increased power steering load. PCM then increases idle speed with the Idle Air Control (IAC) valve.
Primary Heated Oxygen Sensor (HO2S-1)
Measures oxygen content in exhaust gas before catalyst. PCM uses input from this sensor to control duration of fuel injection.
Secondary Heated Oxygen Sensor (HO2S-2)
Measures oxygen content in exhaust gas after catalyst. Determines efficiency of catalytic converter. See OXYGEN SENSOR HEATER under EMISSION SYSTEMS.
Starter Signal
Signals the PCM of engine start-up (cranking). PCM uses this signal to control IAC valve to assist starting.
Top Dead Center (TDC) Sensor
TDC determines ignition timing at engine start-up during cranking and when crank angle is abnormal.
Throttle Position (TP) Sensor
TP sensor is a potentiometer connected to throttle valve shaft. As throttle opening changes, TP sensor develops a proportional voltage signal for PCM. PCM uses this signal to calculate fuel injector pulse duration.
Vehicle Speed Sensor (VSS)
This sensor monitors vehicle speed and generates a signal for the PCM. Sensor produces 4 pulses (switch closures to ground) per revolution of the speedometer cable. PCM uses input from this sensor to calculate timing and fuel injection.
Pressure Switch Signal
This switch sends a signal to PCM indicating VTEC system oil pressure. PCM uses information to control activation of VTEC synchronizer pistons. If failure occurs, PCM will set a Diagnostic Trouble Code (DTC).
OUTPUT SIGNALS
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.
EGR Control Solenoid (EGR-SOL)
See EMISSION SYSTEMS .
EVAP Purge Control Solenoid Valve
See EMISSION SYSTEMS .
Fuel Injectors
See FUEL CONTROL under FUEL SYSTEM.
Fuel Pressure Regulator Control Solenoid Valve
See FUEL DELIVERY under FUEL SYSTEM.
Idle Air By-Pass
See IDLE SPEED CONTROL under FUEL SYSTEM.
Idle Air Control (IAC) Valve
See IDLE SPEED under FUEL SYSTEM.
Ignition Coil Output
See IGNITION SYSTEM .
Ignition Control Module (ICM)
See IGNITION SYSTEM .
Malfunction Indicator Light (MIL)
See SELF-DIAGNOSTIC SYSTEM .
Heated Oxygen Sensor Heaters
See EMISSION SYSTEMS .
PGM-FI Relay
See FUEL DELIVERY under FUEL SYSTEM.
Fuel Pump
Fuel pump is located within fuel tank. When engine is started, PGM-FI main relay operates the fuel pump. When engine is not running fuel delivery stops. A check valve in fuel pump maintains fuel pressure in fuel line when pump is off.
Fuel Pressure Regulator
Fuel pressure regulator maintains a consistent fuel pressure to fuel injectors. A vacuum-operated diaphragm inside regulator maintains fuel pressure within a specific range, allowing for changes in engine load.
At idle, intake manifold vacuum is high, causing diaphragm to be pulled up, thus reducing fuel pressure. When throttle is opened, intake manifold vacuum decreases and causes fuel pressure to increase.
PGM-FI Main Relay
PGM-FI main relay is located above or behind left kick panel. PGM-FI main relay consists of 2 relays. When ignition is on, first relay is energized and supplies battery voltage to PCM, fuel injectors and second relay. Second relay is energized for 2 seconds after ignition is turned on, and whenever engine is running. Second relay supplies battery voltage to fuel pump.
PCM stores basic fuel injector discharge durations at various engine speeds and manifold pressures. Based on stored information and current sensor information, PCM controls injector timing and duration.
Fuel Cut-Off
During deceleration, with throttle valve closed and engine speed more than a preset value, voltage to fuel injectors is cut off. Voltage to fuel injectors is also cut off whenever engine speed exceeds a preset value, regardless of throttle valve position. This is to protect engine from over-revving. See ENGINE SPEED FUEL INJECTOR CUT-OFF .
| Application | (1) Deceleration Engine RPM | (1) Acceleration Engine RPM |
|---|---|---|
| GS-R | 970 | 8100 |
| (1) Fuel injector cut off will occur when engine speed exceeds value. | ||
| (1) | Fuel injector cut off will occur when engine speed exceeds value. |
ENGINE SPEED FUEL INJECTOR CUT-OFF
Throttle Body
Throttle body is a single-barrel side-draft type. Lower portion of throttle valve is heated by engine coolant. Idle adjuster screw (located at top of throttle body) increases or decreases idle air flow when turned. Throttle position sensor is mounted on side of throttle body.
IDLE SPEED CONTROL
Note. For other input components in idle speed circuit, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
Idle speed is controlled by Idle Air Control (IAC) valve and fast idle thermo valve. IAC valve controls amount of air into the intake manifold, according to input signals received from the PCM. The following PCM inputs have influence on IAC valve operation and idle speed
- A/C Clutch Signal
- Alternator FR Signal
- A/T Gear Position
- Brake Switch
- Engine Coolant Temperature Sensor
- Power Steering Pressure Switch
- Starter Switch Signal.
To maintain proper idle speed, the IAC valve controls the amount of air by-passing the throttle body. The PCM determines appropriate idle speed according to various inputs and sends a voltage signal to IAC valve.
Fast Idle Thermo Valve
Valve is mounted on bottom of throttle body and has coolant hoses connected to it. A thermowax plunger inside valve allows additional air to by-pass throttle plate when cold, which in turn increases engine speed. The valve closes when engine warms. No adjustment is possible.
DISTRIBUTOR IGNITION
The ignition coil is grounded (triggered) by the Ignition Control Module (ICM). When coil is grounded, secondary voltage from the ignition coil is then distributed to each spark plug by the distributor.
The ICM is switched on and off by the Engine Control Module (ECM)/Powertrain Control Module (PCM). ECM/PCM uses input signals from Top Dead Center (TDC), Cylinder Position (CYP) and Crankshaft Position (CKP) sensors for basic ignition timing. In addition, ignition timing is influenced by Throttle Position (TP) sensor, Engine Coolant Temperature (ECT) sensor and Manifold Absolute Pressure (MAP) sensor.
DIRECT IGNITION SYSTEM
PCM sends sequential low current signals (one for each coil) to the Ignition Control Module (ICM). ICM in turn grounds each coil in proper sequence and time. Spark plugs are fired directly by coils mounted on each spark plug.
PCM uses input signals from Top Dead Center (TDC), Cylinder Position (CYP) and Crankshaft Position (CKP) sensors for basic ignition timing. In addition, ignition timing is influenced by throttle position sensor, coolant temperature sensor and MAP sensor.
IGNITION TIMING CONTROL
Note. For other inputs, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.
A microcomputer inside PCM controls ignition timing according to engine speed and vacuum within intake manifold. Engine speed and vacuum are transmitted to PCM by signals from Crankshaft Position (CKP) sensor, Cylinder Position (CYP) sensor, TDC sensor, Throttle Position (TP) sensor, Engine Coolant Temperature (ECT) sensor, Knock Sensors (KS), Mass Air Flow (MAF) sensor, and Manifold Absolute Pressure (MAP) sensor.
PCM calculates ignition timing for each engine speed, manifold pressure, and coolant temperature. When these conditions have been processed, PCM sends signals to Ignition Control Module (ICM) to trigger coil(s).
Sensor detects the speed and position of crankshaft. Used for fuel injection timing and ignition timing.
Detects when piston in No. 1 cylinder is at TDC on compression stroke. Used to maintain sequential ignition and fuel injection timing.
Piezo-electric sensor creates small current when detecting a detonation. When knock sensor detects detonation, the PCM will retard ignition timing.
TDC Sensor
This sensor determines ignition timing at start-up (cranking) and when crank position signal is abnormal.
EGR System
The EGR system reduces oxides of nitrogen (NOx) emissions by recirculating exhaust gas into the intake manifold and combustion chambers. The system consists of the EGR valve, EGR vacuum control valve, EGR position sensor, and EGR control solenoid valve.
PCM calculates ideal EGR valve lifts for varying operating conditions. EGR valve lift sensor detects amount of EGR valve lift and sends the information to PCM. PCM compares this information (actual EGR valve lift) with ideal EGR valve lift. If the 2 signals differ, PCM closes EGR control solenoid valve to reduce vacuum applied to the EGR valve.
Evaporative Control System (EVAP)
Consists of an activated charcoal filled canister to store hydrocarbon vapors, a purge solenoid valve and a 2-way valve to prevent excessive pressure or vacuum in fuel tank. This system minimizes fuel tank vapors from escaping into the atmosphere. The PCM allows purge flow at most effective conditions.
Oxygen Sensor Heater
Oxygen sensor heater cuts oxygen sensor warm-up time and stabilizes sensor operation, allowing more accurate determination of exhaust oxygen content. PCM uses this information for calculating injector pulse duration.
Positive Crankcase Ventilation (PCV)
PCV system prevents crankcase blow-by gas from escaping into the atmosphere. PCV valve plunger is lifted in proportion to intake manifold vacuum, drawing engine blow-by gases into intake manifold.
MALFUNCTION INDICATOR LIGHT & LED INDICATOR
PCM supplies a ground for Malfunction Indicator Light (MIL) for about 2 seconds when ignition is first turned on. When a defect is detected in a sensor signal, PCM activates MIL and stores appropriate fault code in memory.
MISCELLANEOUS CONTROLS
Note. Although not true engine performance-related systems, some controlled devices may affect driveability if they malfunction.
A/T Control Solenoid Valves
Transmission Control Module (TCM) controls shift solenoids and torque converter lock-up solenoids.
Note. For other input components, see INPUT DEVICES under COMPUTERIZED ENGINE CONTROLS.