Last Updated on October 22, 2023 by Kevin Chen
The power train or the electronic control system of engines highly depends on the manifold absolute pressure for performing various critical roles. In this guide, we are going to look at everything that you should know about manifold absolute pressure (MAP) sensors. Another aim of this article is to guide you on how to buy the best MAP sensor.
What is a Manifold Absolute Pressure Sensor?
The manifold absolute pressure sensor is used to measure the barometric pressure relative to the atmosphere. It has a very crucial role that plays an important part in many aspects of engine control, including fuel metering, turbocharger/supercharger boost control, valve timing, and more.
Moreover, it can also find its application in measuring altitude or cabin pressure in vehicles.
How it works?
The manifold absolute pressure sensor is located between the intake manifold and the throttle body. It measures the atmospheric pressure that is present in the intake manifold and sends this information to the ECU (engine control unit).
The ECU then uses this data to calculate such things as fuel mixture, ignition timing, and boost pressure. The MAP sensor is a key part of the engine control system and should be kept in good working condition at all times.
MAP sensor works with the intake air temperature sensor to provide input for the air density correction factor. The data is then used to calculate the air density and then the engine load.
In the fuel-injection engine, the manifold absolute pressure sensor works in association with the throttle position sensor to provide input for the air density correction factor. The data is then used to calculate the air density and then the engine load.
For this reason, the intake manifold plays one of the most important roles in determining how much fuel your car’s engine should be injected into the engine cylinders.
When the engine is off, the MAP sensor measures the atmospheric pressure and sends this data to the ECU. When the engine is on, the MAP sensor measures the manifold absolute pressure which is always greater than atmospheric pressure.
What is going on inside a MAP Sensor?
– A vacuum is pulled in through a small hole or port on the side of the sensor.
– This vacuum is then measured and converted into an electrical signal.
– The signal is sent to the engine management system, which uses it to calculate the amount of fuel to inject into the engine.
And that is the working principle of the MAP sensor.
Types of Manifold Absolute Pressure Sensors
The manifold absolute pressure sensors are classified into three types based on various factors. Let us have a look at these different types.
Resistance type sensor
The most commonly used type is this one, often called a ‘resistance-type MAP sensor. It contains a resistor that is in contact with the intake manifold pressure. As the pressure increases, the resistance decreases, and this change is converted into a voltage signal by the sensor. This voltage is then sent to the ECU.
Piezoelectric type sensor
This type of MAP sensor uses a crystal element that generates an electric charge in response to the applied pressure. This voltage is then sent to the ECU. This MAP sensor has certain advantages over the resistance type. For example, it has an unrivaled ability to resist external damage that can cause malfunction.
Capacitance type sensor
This type of MAP sensor uses a capacitor to measure the air pressure. The capacitance of the capacitor changes as the pressure changes and this change is converted into a voltage signal by the sensor. This voltage is then sent to the ECU.
Semiconductor varistor MAP sensor
There is a fourth type of MAP sensor that doesn’t fit into the above three categories. It is called a semiconductor varistor MAP sensor and it uses a variable resistor to measure the pressure. This type of sensor is not very common, but it is becoming more popular due to its reliability and accuracy.
MAP sensors are also grouped according to their designs. The three most common designs are:
Barometric MAP sensor: this type of MAP sensor measures absolute barometric pressure. It is used to determine the altitude and find out how much vacuum or boost is being produced by the engine.
Relative-vacuum MAP sensor: this type of MAP sensor measures relative pressure drop across the throttle plate.
Boost MAP sensor: this type of MAP sensor measures output manifold pressure during forced induction conditions.
MAP sensors are also classified depending on the number of bars that they have. Under this, we have;
2-bar MAP sensor
This type of MAP sensor measures positive and negative pressure that is up to two bars of absolute pressure. It has three terminals and sends a voltage signal to the ECU as the pressure changes.
3-bar MAP sensor
This type of sensor measures positive and negative pressure that is up to three bars of absolute pressure. It also has three terminals and sends a voltage signal to the ECU as the pressure changes.
4-bar MAP sensor
This type of sensor measures positive and negative pressure that is up to four bars of absolute pressure. It also has three terminals and sends a voltage signal to the ECU as the pressure changes.
As you can see, the more bars that the MAP sensor has, the more accurate it becomes at measuring the manifold absolute pressure.
Must I have a MAP sensor in my car?
The MAP sensor is a very important part of the engine management system and it plays a vital role in ensuring that the engine runs smoothly and efficiently. Without a MAP sensor, the engine would not be able to function properly.
So, if your car doesn’t have a working MAP sensor, then you need to take it to a mechanic and get it fixed as soon as possible. It is not something that you want to ignore.
Understanding the internal structure of MAP sensor
The sensor uses a pressure chip to measure the pressure. The pressure chip is a small electronic device that is designed to measure pressure. It has several small holes that allow the air to enter. As the air enters, it pushes on the chip and this causes the electrical resistance to change.
This change is then converted into a voltage signal by the sensor.
The voltage signal is then sent to the ECU, which then interprets the signal to determine the manifold pressure.
The pressure chip is customized depending on the manifold pressure, the type of fuel being used, and other conditions.
This customization ensures that the sensor is giving accurate readings.
Understanding how to interpret a MAP sensor reading
The first step in understanding how to read a MAP Sensor reading is identifying all of its components.
This will help you understand it better. Once you know what each part means, you will be able to decipher the readings.
The figure below shows a typical MAP sensor reading:
DIAGRAM OF MAP SENSOR READING
As you can see, the reading has three main parts: absolute pressure, relative pressure, and vacuum.
Each of these parts has a specific meaning and you must understand what each part means so that you can get accurate readings from the sensor.
Understanding what absolute pressure means
Absolute pressure is a force exerted by gas molecules on a surface. In simple words, this term refers to the amount of air present in a particular area or space. The atmosphere has an approximate sea level pressure of 14.7 psi. So, if you are measuring the absolute pressure at sea level, then 7 psi would indicate a vacuum in your MAP sensor.
The atmosphere also has other pressures at different altitudes. This means that it is not possible to have an average absolute pressure because this would be inaccurate since it does not consider any height variation or location variation.
Understanding what relative pressure means
Relative pressure is the difference between two absolute pressures. It is measured concerning atmospheric pressure, which has an average value of 14.7 psi. Relative pressure can be positive or negative depending on how it relates to atmospheric pressure. For example, if you are measuring the relative pressure at sea level, then 7 psi would indicate a positive pressure or boost.
Understanding what vacuum means
Vacuum is the opposite of absolute pressure and it has an important role to play in MAP sensors. It is measured by assuming that atmospheric pressure is 14.7 psi, which means that the difference between 14.7 psi and any other value would be the vacuum.
A low vacuum reading would indicate that there is a lot of air present in the sensor and a high vacuum reading would indicate that there is very little air present.
What do I need to know about working with MAP sensors?
A number of precautions need to be taken when working with a MAP sensor. For starters, make sure that you always disconnect the negative battery cable before starting anything related to the engine management system.
Another precaution is to prevent any high voltage from entering into your sensors. Take care not to touch the inside of the sensor while it is plugged in.
What happens when the MAP sensor goes bad?
A bad MAP sensor can cause a number of problems in your engine. One of the most common symptoms is a decrease in power and performance. This is because the sensor plays an important role in determining how much fuel to inject into the engine.
If the sensor is not working properly, then it will not be able to provide accurate information to the engine. This can lead to a variety of problems, including:
– Lean running condition
– Hesitation or stumble
– Rough idle
– Lack of power
– Increased emissions
If you experience any of these symptoms, your MAP sensor likely needs to be replaced.
What do I need to know about replacing the MAP sensor?
– Always disconnect the negative battery cable before attempting to replace any sensors on your vehicle
– Keep high voltage out of your new MAP sensor. If you touch the wrong terminals, it can potentially damage your new sensor or even cause an electrical shock.
– If you need to remove the old MAP sensor, do not use a screwdriver or anything else that conducts electricity. This will risk damaging your new sensor.
– Be sure to follow your vehicle manufacturer’s instructions when installing the new MAP sensor.
How to buy MAP sensors?
You can find a number of MAP sensors from reliable suppliers and manufacturers. When shopping for a new sensor, be sure to consider the following factors:
– The type of sensor – There are a variety of MAP sensors on the market, so make sure you select the right one for your vehicle.
– The size of the sensor – This will be determined by the mounting location and the available space.
– The electrical connectors – Make sure that you get the correct connector for your vehicle.
– The sensor specifications – Make sure that all of the specifications on the new MAP sensor are compatible with your car.
How to test a MAP sensor?
Testing a MAP sensor usually requires a multimeter or a scan tool. You can use the following steps to test the MAP sensor using a multimeter:
– Start by disconnecting your vehicle’s battery
– Disconnect your MAP sensor from its electrical connector
– Now, set up your multimeter so that you are measuring the voltage between the 5 volts and 12 volts range. A low voltage reading (below 5 volts) would indicate that your MAP sensor is bad.
– Next, measure the resistance between the two terminals on your MAP sensor. A high resistance reading (above 1,000 ohms) would indicate that your MAP sensor is bad.
You can also test a MAP sensor with a scan tool. The scan tool will connect to the sensor’s electrical connector and perform a multistep test. The last result in this test will tell you whether your MAP sensor is good or bad.
Conclusion
Manifold Absolute Pressure (MAP) Sensor is an important component in your engine management system. It provides information about how much air is present inside the manifold. This information is used to calculate the amount of fuel that needs to be injected into the engine.
A bad MAP sensor can cause a number of problems, including decreased power and performance. If you experience any of these problems, your MAP sensor likely needs to be replaced.
You can find several MAP sensors at ICRFQ. We are a reliable supplier and sourcing agent of MAP sensors in China. We offer the best quality MAP sensors at affordable prices. If you want to buy or replace your own MAP sensor, take that noble step of contacting us.
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