PRE-RELEASE
Mass air flow sensor unit (686), Simtec
| Mass air flow sensor unit (686), Simtec |
| Location |
Mass air flow sensor (205)
Intake air temperature sensor (407)
| Principal use |
Sends information on air mass flow to the control module and serves as main sensor for fuel injection.
| Type |
The mass air flow sensor contains two PTC resistors, which are located in the air flow. One resistor measures the temperature of the flowing air while the other measures air mass flow. As two fixed resistors, they form a component of the wheatstone bridge.
The mass air flow sensor also contains an NTC resistor to provide the control module information on current intake air temperature.
| Connection |
| Pin No. | Signal type | Description |
| 1 | Signal | Intake air temperature sensor's output to ECM pin 41(A). |
| 2 | Ground | Mass air flow sensor's ground, also intake air temperature sensor's ground to EMC pin 27(A). |
| 3 | Output | Mass air flow sensor's output to ECM pin 43(A). |
| 4 | Power supply, B+ | Sensor's power supply from the main relay. |
The mass air flow sensor contains two PTC resistors, which are located in the air flow. One resistor measures the temperature of the flowing air while the other measures air mass flow. As two fixed resistors, they form a component of the wheatstone bridge. The resistors in the air flow are warmed by being supplied voltage by an operation amplifier.
The operation amplifier measures the voltage from the bridge. When air flow increases, a higher voltage is required to keep the temperature difference constant. The required voltage is converted to a suitable voltage interval and is sent out on pin 3.
The mass air flow sensor is grounded in ECM pin 27(A) and is supplied power from the main relay to ground.
ECM coverts the voltage on pin 43(A) to grams of air per second and then, using the value from the crankshaft position sensor, to milligrams of air per combustion. This unit is written as mg/c (milligrams per combustion) and constitutes the primary measurement value for fuel injection. 14.7 mg/c normally uses 1 mg fuel. This value is also a good gauge of engine torque or load.
