Engine Sensors and How They Influence Fuel Flow
The functions of today’s fuel injected engines rely completely on a powertrain control module (PCM) and its associated sensors, of which there are many. Fuel has the ability to adapt to altitude, temperature, humidity, and load while maintaining a constant fuel ratio of 14.7:1.
In order for the PCM to prepare fuel flow strategies, it uses sensors to determine the demand on the engine and its operating environment.
When the check engine light has illuminated, it means the PCM has determined a problem exists in a system. The cause could be a sensor, PCM, wiring, component, internal engine or transmission issues.
PCM Related Sensors And Their Effect On Fuel Flow
Mass Airflow Sensor (MAF): This is a sensor that measures the amount of airflow into the intake manifold. It does so with the use of a “hot wire” in the center of the sensor opening.
The PCM sends a voltage to heat the wire to a predetermined temperature. As the volume of air increases over the wire, in effect cooling the wire, more voltage is necessary to maintain the temperature.
The PCM senses the voltage increase and adjusts the fuel flow to match the increase in air volume.
Throttle Position Sensor (TPS): This is a potentiometer attached to the opposite side of the throttle plate in the throttle body. At closed throttle, the TPS signals 0.5 volts and increases to 4.5 to 5.0 volts at wide-open throttle.
The PCM senses the speed and amount of opening and recognizes this as an increased power demand and adjusts the fuel trim and injector duration to supply the necessary increase in fuel yet maintain the fuel ratio.
Knock Sensor (KS): Positioned on the side of the block or in the center of the intake manifold, this sensor signals spark knock or pre-ignition that is damaging. In response, the PCM will retard the spark and adjust the injector duration to prevent the knock.
Coolant Temperature Sensor (CTS): This sensor is usually located near the thermostat and signals the engine coolant temperature. The PCM richens the mixture when cold and adjusts the fuel trim as the engine coolant temperature increases.
Oxygen Sensor (Ox): This sensor is located in the exhaust system and senses the amount of unburned oxygen in the exhaust system as an indication of the fuel mixture. High amounts of the oxygen signal a lean mixture which causes NOX pollutants and detonation harmful to engine components.
Too little oxygen denotes a rich mixture that is harmful to the catalytic converter and reduces fuel economy. The PCM continually adjusts the fuel mixture to maintain the proper mixture under all phases of engine demand.
Intake Air Temperature (IAT): This sensor is typically located in the air intake ducting to the throttle body. The PCM takes this information into account when adjusting the fuel trim.
Camshaft Sensor (CMS): This is either a hall effect sensor or magnetic pickup located in the valve cover or engine block near the camshaft. It senses the position of the camshaft in relation to the crankshaft. The PCM uses this to adjust the injector and engine timing.
Crankshaft Position Sensor (CKS): This is also a hall effect or magnetic pickup sensor located on the front of the block near the crankshaft harmonic balancer, on the side of the engine block or in the back of the block. The sensor generates a signal and sends it to the PCM when it senses trigger wheel movement. The trigger wheel is either attached to the crankshaft, harmonic balancer or flywheel.
This sensor signals the position of top dead center on the number one cylinder and the rate of engine rpm for ignition timing, misfire detection, and fuel delivery purposes.