Sensors for air and coolant temperature are next on the list. They too will send data to the ECU to adjust the air-fuel mixture. The Internal Air Temperature (IAT) sensor works during start-up to determine the amount of fuel required by the engine to ensure steady idling at a low temperature. It also controls the enrichment of the air-fuel mixture and, in some cases, the air flow during the idling process.

As for the Engine Coolant Temperature (ECT) sensor, it will negatively alter the mixture as the engine warms up. However, it also works to prevent engine overheating. How? By sending a signal to the ECU to enrich the air-fuel mixture, which will momentarily reduce the internal temperature and prevent serious damage. The ECU will send an error message and potentially cut the power delivery as a safety measure to prevent engine breaks.


The crankshaft sensor (CKP), which receives an impulse after each engine revolution, sends pulsating AC to the computer. This current is transformed and redirected to an internal module which calculates the number of engine revolutions. A signal is then sent to the tachometer to inform the rider about real-time engine speed. The electronic module also needs this signal for the injection sequence.

Some systems use a camshaft sensor (CMP). Each camshaft rotates once while the crankshaft rotates twice (4-stroke engines only). This sensor monitors the positioning of the piston during its ascending course and sends an impulse to the ECU which will adjust the start of the injection to account for any increase in engine speed.

An engine knock sensor can be added to address combustion problems. It senses excessive vibrations produced by a false detonation or pre-ignition and quickly steps in to delay the ignition process as long as the "knock" is felt. This sensor uses a piezo-electric element mounted on a vibrating plate. It produces and sends a tension to the computer, which converts the signal and makes ignition corrections to prevent fuel from detonating inside the cylinder.

Finally, if the system features a catalytic converter, you might see an oxygen sensor (or Lambda sensor). This unit determines if the air-fuel ratio exiting the engine is rich (with unburnt fuel vapor) or lean (with excess oxygen). Closed-loop feedback-controlled fuel injection varies the fuel injector output according to real-time sensor data rather than operating with a predetermined (open-loop) fuel map. In addition to improving overall engine operation, it reduces the amounts of both unburnt fuel and nitrogen oxides (NO_x) entering the atmosphere.


Photo Credit : Henri Lebarbé