What is the Principle of operation of the MAP sensor?

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Principle of operation of the MAP sensor:

MAP is connected to the manifold through a vacuum hose. The vacuum within the manifold actuates the MAP sensor’s diaphragm. The converter transforms the measured pressure into an electrical signal which is fed into the onboard controller. ECU estimates the info from the MAP sensor values as: “Absolute Pressure” = “Atmospheric pressure” – “manifold pressure”.

By using the speed/density method, the onboard controller calculates the fuel mixture composition counting on the signal of MAP and engine speed. This method is predicated on the idea that with every turn the engine sucks a hard and fast volume of air. The accuracy of this method cannot be compared therewith of the air quantity sensor, which after the accurate measure of the airflow calculates the fuel mixture ratio supported mass or volume of air sucked in from the engine.

When there’s a high level of vacuum within the manifold (e.g. idling), the MAP sign is comparatively low and therefore the onboard controller provides less fuel.

In systems with a “wet” type manifold (e.g. SPi), changes in manifold pressure can cause the fuel entering the vacuum hose to achieve the MAP. To avoid this, a special trap is employed and accordingly traced the vacuum hose. If the fuel reaches the MAP sensor, its diaphragm could also be damaged.

In MPi systems the manifold could be a “dry” type and fuel can’t enter because it is sprayed over the intake valves. Therefore there’s no risk of MAP sensor fuel penetration and contamination of the diaphragm, and thus a special trap isn’t used.

When the MAP sensor is employed as a separate component, inexpensive maintenance may be achieved. When the MAP sensor is constructed into the onboard controller, a possible replacement of the MAP would require the replacement of the full controller.

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