The manifold absolute pressure sensor (MAP sensor) is one of the sensors employed in an enclosed combustion engine’s electronic system.
Engines that use a MAP sensor are typically fuel injected. The manifold absolute pressure sensor provides instantaneous manifold pressure information to the engine’s electronic control unit (ECU). The info is employed to calculate air density and determine the engine’s atmospheric state rate of flow, which successively determines the specified fuel metering for optimum combustion (see stoichiometry) and influence the advance or retard of ignition timing. A fuel-injected engine may alternatively use a mass airflow sensor (MAF sensor) to detect the intake airflow. A typical naturally aspirated engine configuration employs one or the opposite, whereas forced induction engines typically use both; a MAF sensor on the charge pipe resulting in the throttle body and a MAP sensor on the intake tract pre-turbo.
MAP sensor data is converted to atmosphere data by employing a second variable coming from an IAT Sensor (intake air temperature sensor). This is often called the speed-density method. Engine speed (RPM) is additionally wont to determine where on a lookup table to work out to fuel, hence speed-density (engine speed/air density). The MAP sensor can even be utilized in OBD II (on-board diagnostics) applications to check the EGR (exhaust gas recirculation) valve for functionality, an application typical in OBD II equipped General Motors engines.
What are the Symptoms of a Failing MAP Sensor?
Symptoms of a Failing Manifold Absolute Pressure Sensor:
A failed MAP sensor has serious implications on fuel control, vehicle tailpipe emissions, and fuel economy. Symptoms of a nasty or failing MAP sensor include:
Excessive fuel consumption:
A MAP sensor that measures high manifold pressure indicates high engine load to the PCM. This leads to a rise in fuel being injected into the engine. This, in turn, decreases your overall fuel economy. It also increases the number of hydrocarbon and CO emissions from your vehicle to the encircling atmosphere. Hydrocarbons and carbon monoxide gas are a number of the chemical components of smog.
Lack of power:
A MAP sensor that measures low manifold pressure indicates low engine load to the PCM. The PCM responds by reducing the number of fuel being injected into the engine. While you’ll notice a rise in fuel economy, you may also notice that your engine isn’t as powerful because it was before. By reducing the fuel into the engine, combustion chamber temperatures are increased. This increases the number of NOx (oxides of nitrogen) production within the engine. NOx is additionally a chemical component of smog.
Failed emissions test:
A bad MAP sensor will cause your vehicle to fail an emissions test. Your tailpipe emissions may show a high level of hydrocarbons, high NOx production, low CO2, or a high level of CO.
What is the Principle of operation of the MAP sensor?
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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