Glossary of Common Terms
BAS – Bank Angle Sensor
This sensor is located in the turn signal module and it sends a signal to the ECM if the bike leans over more than 45° from vertical. If the ECM gets this signal for more than one second it assumes the bike fell over and it shuts down both the fuel management and ignition circuits.
CKP – Crank Position Sensor
This sensor provides input signals to the ECM that indicate engine rpm, (how fast the engine is running in Revolutions Per Minute). The ECM also uses these inputs to determine what stroke the engine is in so it can deliver the fuel and spark at the desired time.
ECM – Electronic Control Module
This is the brain of the system that collects input signals from multiple sensors, makes decisions and sends output signals to deliver fuel and spark to the engine.
Electric Fuel Pump
A 12-volt high-pressure fuel pump, (located in the fuel tank) supplies fuel under pressure to the fuel injectors
ET – Engine Temperature
This sensor provides input signals to the ECM as it reacts to the temperature of the front cylinder head of Softails and Touring model motorcycles. The ECM uses the signals from this sensor to determine if the engine is at operating temperature, or warming up.
Fuel Injectors
The fuel injectors are electric valves that open and close to deliver a high-pressure spray of fuel directly at the intake valve. They are controlled by output signals from the ECM to deliver fuel at a precise moment, (just before the intake valve opens). If more fuel is needed, the ECM will signal the injector to remain open for a longer period of time. The period of time is known as the injector "pulse width" and is measured in milliseconds. One method of rating fuel injectors is by their flow rate – such as in gm/sec, or grams per second.
Fuel Pressure Regulator
A mechanical device that controls fuel pressure to 55-62 PSI by returning excess fuel from the fuel pump back to the fuel tank. The regulator is located inside the fuel tank on Softails and Touring model bikes
IAC – Idle Air Control
An electric valve that’s threaded, (each rotation is a "step") and controlled by output signals from the ECM to open and close as needed to allow enough air into the engine for starting and idle operation. The greater the number of IAC steps, the greater the amount of air enters the engine through the IAC passages.
IAT – Intake Air Temperature
This sensor provides input signals to the ECM as it reacts to the temperature of the air entering the engine. For example, hot air has less oxygen in it than cool air. The ECM uses the inputs from this sensor to help calculate how much oxygen exists in a quantity of air.
Ion Sensing System
This system uses ion-sensing technology to detect detonation or engine misfire in either the front or rear cylinder by monitoring the electrical energy at the spark plug following every timed spark. If an abnormal level of energy is detected across 2 or 3 spark firings the ECM responds by retarding spark timing in the problem cylinder as needed to eliminate it.
MAP - Manifold Absolute Pressure
This sensor provides input signals to the ECM and reacts to intake manifold pressure and ambient barometric pressure. Intake manifold pressure reflects changes in engine speed and load. Ambient barometric pressure reflects changes in atmospheric pressure caused by weather conditions or changes in altitude. The ECM uses the inputs from this sensor to help calculate how much air is entering the engine.
TPS – Throttle Position Sensor
This sensor provides input signals to the ECM as it reacts to throttle shaft rotation, telling the ECM throttle position, if the throttle is opening or closing, and how fast it’s opening or closing.
VE - Volumetric Efficiency
Volumetric efficiency is a percentage rating of how much air is flowing through the engine while running as compared to its theoretical capacity.
For example, an engine with a displacement of 88-cubic inches running at 5600 rpm at full throttle has a theoretical airflow capacity of 100% when it flows about 143-cubic feet of air per minute, (cfm). If the same engine flows 107cfm at 5600 rpm it would have a VE of about 75%.
If the engine flows about 157cfm at 5600 rpm it would have a VE of about 110%. Note the VE can exceed 100%, especially in high performance engines that have improved airflow through the engine. VE reacts to engine speed and to anything that increases or decreases airflow through the engine.
VSS – Vehicle Speed Sensor
This sensor provides input signals to the ECM to indicate if the bike is moving or sitting still. It is used mostly to assist the control of idle speed.
BAS – Bank Angle Sensor
This sensor is located in the turn signal module and it sends a signal to the ECM if the bike leans over more than 45° from vertical. If the ECM gets this signal for more than one second it assumes the bike fell over and it shuts down both the fuel management and ignition circuits.
CKP – Crank Position Sensor
This sensor provides input signals to the ECM that indicate engine rpm, (how fast the engine is running in Revolutions Per Minute). The ECM also uses these inputs to determine what stroke the engine is in so it can deliver the fuel and spark at the desired time.
ECM – Electronic Control Module
This is the brain of the system that collects input signals from multiple sensors, makes decisions and sends output signals to deliver fuel and spark to the engine.
Electric Fuel Pump
A 12-volt high-pressure fuel pump, (located in the fuel tank) supplies fuel under pressure to the fuel injectors
ET – Engine Temperature
This sensor provides input signals to the ECM as it reacts to the temperature of the front cylinder head of Softails and Touring model motorcycles. The ECM uses the signals from this sensor to determine if the engine is at operating temperature, or warming up.
Fuel Injectors
The fuel injectors are electric valves that open and close to deliver a high-pressure spray of fuel directly at the intake valve. They are controlled by output signals from the ECM to deliver fuel at a precise moment, (just before the intake valve opens). If more fuel is needed, the ECM will signal the injector to remain open for a longer period of time. The period of time is known as the injector "pulse width" and is measured in milliseconds. One method of rating fuel injectors is by their flow rate – such as in gm/sec, or grams per second.
Fuel Pressure Regulator
A mechanical device that controls fuel pressure to 55-62 PSI by returning excess fuel from the fuel pump back to the fuel tank. The regulator is located inside the fuel tank on Softails and Touring model bikes
IAC – Idle Air Control
An electric valve that’s threaded, (each rotation is a "step") and controlled by output signals from the ECM to open and close as needed to allow enough air into the engine for starting and idle operation. The greater the number of IAC steps, the greater the amount of air enters the engine through the IAC passages.
IAT – Intake Air Temperature
This sensor provides input signals to the ECM as it reacts to the temperature of the air entering the engine. For example, hot air has less oxygen in it than cool air. The ECM uses the inputs from this sensor to help calculate how much oxygen exists in a quantity of air.
Ion Sensing System
This system uses ion-sensing technology to detect detonation or engine misfire in either the front or rear cylinder by monitoring the electrical energy at the spark plug following every timed spark. If an abnormal level of energy is detected across 2 or 3 spark firings the ECM responds by retarding spark timing in the problem cylinder as needed to eliminate it.
MAP - Manifold Absolute Pressure
This sensor provides input signals to the ECM and reacts to intake manifold pressure and ambient barometric pressure. Intake manifold pressure reflects changes in engine speed and load. Ambient barometric pressure reflects changes in atmospheric pressure caused by weather conditions or changes in altitude. The ECM uses the inputs from this sensor to help calculate how much air is entering the engine.
TPS – Throttle Position Sensor
This sensor provides input signals to the ECM as it reacts to throttle shaft rotation, telling the ECM throttle position, if the throttle is opening or closing, and how fast it’s opening or closing.
VE - Volumetric Efficiency
Volumetric efficiency is a percentage rating of how much air is flowing through the engine while running as compared to its theoretical capacity.
For example, an engine with a displacement of 88-cubic inches running at 5600 rpm at full throttle has a theoretical airflow capacity of 100% when it flows about 143-cubic feet of air per minute, (cfm). If the same engine flows 107cfm at 5600 rpm it would have a VE of about 75%.
If the engine flows about 157cfm at 5600 rpm it would have a VE of about 110%. Note the VE can exceed 100%, especially in high performance engines that have improved airflow through the engine. VE reacts to engine speed and to anything that increases or decreases airflow through the engine.
VSS – Vehicle Speed Sensor
This sensor provides input signals to the ECM to indicate if the bike is moving or sitting still. It is used mostly to assist the control of idle speed.