Guest Blogger: Street Rod 101
The manifold absolute pressure (MAP) sensor is used to measure the absolute pressure (also called vacuum) inside of the intake manifold. It is used on all computerized engine systems. It is considered one of the many inputs to the computer to more precisely control the air fuel ratio during engine operation. This is expecially important when determining how much load is on the engine. Inside of the intake manifold, there is a vacuum produced by the pistons drawing in air and fuel. In most cases, it is considered a vacuum. However, the MAP sensor on the intake manifold is reading a pressure. This causes some confusion.
pressures and vacuums. Intake manifold vacuum can now be stated as a pressure. MAP readings on the psia scale would be considered vacuum readings on the psig scale.
There are several types of MAP sensors. One common type is a MAP sensor that uses a flexible-type resistor. When the resistor is flexed (because of an increase in manifold pressure), its resistance changes. This change causes a voltage drop that the engine computer uses to control the fuel injection process. On some vehicles a diaphragm uses a pressure-sensitive disk capacitor. A varying voltage frequency signal is produced to represent intake manifold absolute pressure changes.