How to properly test your MAP sensor.

How to test amapnd see if you are getting the best fuel economy that you should be getting!

With rising gas prices, the best possible fuel economy is wanted by everyone who drives.  There is one simple test that you can do that will be able to tell you if you are getting the best fuel mileage that you can and should be getting.  This article will go through this test and give you the simple procedure to test this on your own.

The test is a manifold vacuum test.  This test sounds like it has nothing to do with fuel economy, but it has everything to do with it.  This test is so simple to accomplish, yet it is so often overlooked by mechanics.  So if your vehicle’s fuel economy has dropped dramatically then you may need to do this test.

The manifold vacuum test will help you to determine if your MAP sensor is receiving the correct vacuum readings.  This is vital, because the MAP sensor is what controls how much fuel is injected into the engine.  If you have a vacuum leak in a hose going to your MAP sensor this will show that there is no vacuum present and the MAP sensor will think that your vehicle is under a heavy load and is at a wide open throttle.  This will make your computer inject more fuel, thus making your vehicle drastically lose fuel mileage. 

When testing your manifold vacuum you are going to need to understand that you will have a vacuum between about 0 inches of vacuum all the way up to around 21 inches of vacuum.  As long as you are in that general range then your vehicle is running in top shape.  We will now discuss the procedure.

The Procedure

  1. You are going to want to open your hood and locate some service related information on your vehicle.  The internet should be able to help.
  2. With the proper service information you are going to want to locate your MAP sensor on your vehicle.  Use the information that you gathered and locate this.
  3. You are then going to want to remove the vacuum hose from the MAP sensor.  This is where you are going to test from.
  4. To test the vacuum at the hose to the MAP sensor you are going to need to purchase a vacuum tester like this KDT3683 Vacuum Pump.  This vacuum tester has a pump to provide vacuum when you need to, it also comes with multiple adapters to allow you to adapt to and fit many different size hoses and sensors.
  5.  Next you are going to have to get the help of another person.  This person is just going to have to start the vehicle, while you connect your vacuum gauge.  If you cannot get the help of someone else you can just connect your KDT3683 Vacuum Pump to the vacuum hose to the MAP sensor and make sure that the vacuum pump is not going to hit any moving parts on the engine.  Then you will want to start your vehicle, it may run rough just to warn you.
  6. Once you have your engine running you are going to want to go look at your KDT3683 Vacuum Pump gauge and read the gauge.  You should have between 15inches of vacuum and 21 inches of vacuum on the gauge at idle.  If you have anything lower your vacuum hose to your MAP sensor may be leaking causing you to have this reading.  This could be one of the causes of your poor fuel mileage.
  7. You can next test the vacuum off idle to see what it is.  It should be between 0 inches and 21 inches of vacuum.  This will just insure that your vehicle is in good running condition.
  8. If your KDT3683 Vacuum Pump read below 15 inches when you tested at idle you are going to want to do some further testing.
  9. The testing is fairly simple.  You will just need a ATD5540 Multimeter and your KDT3683 Vacuum Pump.  The first test that you are going to want to do is a voltage reference test.  To do this you are going to want to remove the connector.  Then connect your ATD5540 Multimeter with the red to the voltage wire, and the black to a good ground, I recommend the negative post of the battery.  You should have around 5 volts DC.
  10. If you do not have 5 volts then you may have a wiring problem or the MAP sensor may be bad, I would recommend taking it to a mechanic for further diagnosis.  If you have 5 volts continue to the next step.
  11. Next you are going to want to remove the vacuum hose from the MAP sensor.  Then test the same wire to the negative battery post and you should have 4.5-5 volts.
  12. If that passes then you will want to KDT3683 Vacuum Pump and apply 5 inches of vacuum and check the voltage and it should be around 3.75 volts.
  13. The last test that you will want to do if it passes is to apply 20 inches of vacuum and you should have a reading around 1.1 volts.
  14. If your MAP sensor passed all of those test it is working correctly, and I would recommend taking your vehicle to a shop and have it further diagnosed.  If it failed any one of steps 11-13 then you likely have a faulty MAP sensor.

You just finished testing your MAP sensor, and you likely fixed the poor gas mileage of your vehicle.

Written by: Cody Mammenga an NDSCS Student

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