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Understanding Your Car’s MAP – Here’s What You Need To Know

Understanding Your Car’s MAP – Here’s What You Need To Know

The manifold absolute pressure sensor (MAP sensor) is used in an internal combustion engine‘s electronic control system.

Auto Repairs Are EXPENSIVE

Fuel-injected engines use a MAP sensor. The manifold absolute pressure sensor transmits manifold pressure data to the engine's electronic control unit (ECU). The information will then be used to calculate air density and figure out the engine's air mass flow rate.  The MFR will then be employed to pinpoint the fuel metering for optimum combustion. It will also determine if the ignition timing should advance or retreat. 

A MAP is an alternative to a mass airflow sensor (MAF sensor). They are both used to detect intake airflow. Forced induction engines typically use both kinds of sensors. In a car with a forced induction engine, there will be a MAF sensor on a charge pipe that leads to the throttle body. There is also a MAP sensor on the intake tract.

Symptoms of a Bad Map Sensor

The Engine Control Module uses MAP sensor information to perform important calculations, like engine load. The MAP sensor reads atmospheric pressure at sea level when it is not in use. 


When an automobile is idling, the intake pressure will be somewhere between 16-22 in. Hg. Because this is lower than atmospheric pressure, air rushes into the intake. When the brake pedal is depressed, the pressure might go down to 10 in. Hg. when the car speeds up, the open throttle body permits air to enter very quickly, increasing pressure in the intake. When the throttle is completely opened, intake and atmospheric pressure will be the same.


You are Not Getting the Same Number of Miles per Gallon

If the ECM says there is no vacuum, it thinks the engine is at high load. When it does this it releases fuel and advances spark timing. This will cause the car to use too much gas. It is not a good idea to drive your car if this is the case. Not only will your car get bad gas mileage, but the fuel may also pre-ignite or auto-ignite in an engine's combustion chamber and that can be very dangerous.

The Car is Lagging

If the ECM says you have a high vacuum, it thinks the engine load is low. When this happens, the fuel injection is cut down and that slows spark timing. When too little fuel is released, you will have a hard time accelerating.

If your MAP sensor is broken it may lead to an increase in emissions. Excessive fuel generates higher hydrocarbon (HC) and carbon monoxide (CO) emissions. If you have too little fuel, it can create high nitrogen oxide (NOx) emissions.

The Car is Rough Idling or Hard Starting 

When a car doesn’t get enough fuel, it may lead to the cylinder misfiring and vehicle rough idling. A car needs gas to run and if it doesn’t get enough nourishment, its tummy will grumble.

A very rich or lean mix will cause the ignition to be hard to start. When you have to depress the gas peddle to start the car, it is likely that there is something wrong with the MAP.

The Car Stalls or Hesitates 

If you are at a stop sign and the car hesitates or stalls out, the EMC may be releasing too little gas based on the MAP’s false information.

Before taking your vehicle into a mechanic, you may want to perform a check to make sure that there actually is something wrong with it. A mechanic may take your car for the day and charge you plenty just to tell you that your MAP is shot. It is fairly easy to check the component.

Step 1

Find the MAP sensor and the firewall. 

Step 2

Make sure the vacuum hose attached to the sensor is not damaged and free of obstructions. You should also check for any loose wires.

Step 3

Now it is time to perform the test. If you have a voltage type of MAP unit, you will use a voltmeter for this test; if it is a frequency type of MAP, you will use a tachometer. 

Step 4

Be sure to unplug the electrical connector from the MAP sensor. Turn your key in the ignition, but do not press the gas pedal. If you have a voltmeter, you should measure the reference voltage. You can do this by touching the reference wire against the meter’s positive lead.  You should then put the negative lead to the ground-black wire. If the reference voltage is not, at least 5 volts,  you have found the problem. You should get your car to a mechanic right away.

Step 5

Connect the meter’s negative probe to the ground wire. attach the positive probe to the signal wire. 

If the sensor's connector is not plugged in, plug it in. The third wire is called the reference wire and it should always produce a steady 5-volt signal. It is a good idea to insert pins into the wires to attach the probes to for this test.

Step 6

Detach the vacuum hose from the MAP sensor, you should then attach a hand vacuum pump.

Step 7

Turn the ignition key on, but do not start the engine.

Step 8

Read the voltage or rpm. The reading should be between 4.5 and 5 volts, or between 300 and 320 rpm.

Step 9

Finally, you should use your meter to apply 5 in-Hg of vacuum. Look at the meter’s reading again, it should be around 3.75 volts, or between 275 and 295 rpm.

If the readings are not what they should be, you may have to replace the MAP Sensor.

How much is a MAP sensor?

If you do need a new sensor, you should get one as soon as possible. A bad MAP sensor will not only cause your car to run rough, but it can also cause damage to your engine.  It should cost around  $130 and $200 for a new MAP sensor. Labor should be fairly inexpensive in this case and it may even be free.  It is very easy to install a sensor yourself.


How do you install a sensor?

Disconnect Everything

Before you begin, you will want to open the hood and take the engine cover off with the appropriate kind of screwdriver. Be sure to disconnect the negative side of your battery. Remove the air cleaner and the intake.


You will find the MAP located next to the distributor. Disconnect the electrical line and the vacuum line. You will need a ratchet to remove the old sensor. The sensor will be attached to a removable bracket, so take the old bracket out. 

Mount the New Sensor

Attach the new sensor onto the removable bracket. You will need to mount your new sensor inside the engine bay area. When replacing an old sensor, simply remove it and put the new one in the exact same place. 


Vacuum Line and Wires

The sensor will need to be attached to the vacuum line. You can tie it to the vacuum line that goes to the BOV. Simply connect the vacuum line that runs from the sensor to the vacuum.  You will run all of the sensor wires through the firewall. You must then wire the sensor into the power source of the old MAP sensor. 

Plugin the New Sensor

You should be able to plug in your new sensor and put everything back together right away. However,  Some MAP sensors have multiple plugs. So you should use your owner’s manual to find out which ones to use. 

Although it is an awfully simple operation to perform, a lot of people will still choose to go to a mechanic rather than touching the inside of their car. If you decide to have the work done in a shop, you will have a couple of options.

You can take your car to the dealership where you bought it or to a dealership that services your brand of car. Although they will be more expensive than going to an autobody shop, they will also have any parts that may be necessary on hand. The mechanics will be trained in your brand of car. 

You can also take your car to an autobody shop. The auto body shop will charge you much less money than the dealership would. Replacing a MAP is not especially detailed work, so in this case, the mechanic who works on your car will not need special training in your make and model of auto. An independent mechanic is definitely the best option for replacing a MAP.

If you have a million other problems with your car in addition to needing anew MAP or if you are just looking for a change, you can always sell your old car and buy a new one. Old cars are worth money and there are a few ways you can get cash for your old automobile. 


Sell Your Car Online

When you Google, “sell my car online” quite a few sites will come up. These websites will charge you a fee to list your car online. You will have a lot of competition if you sell your vehicle this way. You may have to have your ad up for several months before you even get a potential buyer.


Once you do get a call, you will have to take the time to show them the car. You may have to show the car to a few people before actually selling the vehicle. Most people who are in the market for junk cars are mechanics and they may just want to buy a part or two.

Selling your car on a general online billboard is not a good idea. Thieves, human traffickers, and killers have found victims online using electronic billboards.


Trade-In Your Car

If you are going to buy a new car, the salesperson will offer you a trade-in allowance for your old vehicle. Normally, they will offer you far less than they should. It is always a good idea to explore other options before trading your car in. 


Another thing a dealer might do is give you what seems to be a terribly fair price for your junk car. If they do this, you should go over your final offer very carefully. Check that they have not added the trade-in that they gave you right back on to the final price of your vehicle.


When you go into the dealership, it is a good idea not to mention that you have a car to trade-in. Get them to give you a final price in writing and then tell them about the trade-in. 


Sell Your Car to Us

Selling your car to Cash Cars Buyers is simple. Just fill out our online form with a few simple facts about you and your car.


Our form asks for your name, email address, and phone number. We will also want to know the year, make, model, and VIN number. We are primarily interested in cars manufactured after the year 2002.


When we get your form, we will call you back with an offer. If you accept it, we will make an appointment to come to get your car. Our team member will arrive right on time, pay you in cash, and tow the car away. 


If you sell your car online or use it as a  trade-in, you will have to have the title. If you don’t have the title, you will have to get a new one. In most cases, no title is no problem for us, so fill out the form today.