How To Test The MAP Sensor (Ford F150, F250, F350)

This tutorial will help you to test the manifold absolute pressure (MAP) sensor using a multimeter.

You'll be able to easily find out if the MAP sensor is bad or not in three simple test. All of them are explained in a step-by-step manner to easily help you find out if the MAP sensor is bad or not.

APPLIES TO: This tutorial applies to the following vehicles:

• Ford Bronco 4.9L, 5.0L, 5.8L: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996.
• Ford F150 4.9L, 5.0L, 5.8L: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996.
• Ford F250 4.9L, 5.0L, 5.8L: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996.
• Ford F350 4.9L, 5.8L: 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.

Symptoms Of A Bad MAP Sensor

The MAP sensor is a critical engine management system component, so when this bad boy fails, engine performance is going to suffer!

Here is a basic list of the symptoms you'll see when the MAP sensor fails:

1. You'll see one of the following trouble codes:
   • Code 22: MAP Sensor Out of Range.
   • Code 72: Insufficient MAP Change During Dynamic Response Test.
   • Code 126: MAP/BARO Sensor Higher Or Lower Than Normal.
   • Code 128: MAP Sensor Vacuum Hose Damaged or Disconnected.
   • Code 129: Insufficient MAP Change During Dynamic Response Test KOER.
2. You'll also experience:
   • Engine cranks for a long time before it starts.
   • When the engine starts, you get a lot of black smoke coming out of the tail-pipe.
   • Engine stalls as soon as it starts.
   • If the engine stays running, it idles very rough.
   • If the engine runs, you'll get really bad gas mileage.

What Does The MAP Sensor Do?

The fuel system in your Ford vehicle is a ‘Speed Density’ type. In lay man's terms, this means two things:

• That the PCM uses MAP sensor signal info and RPM input (from the PIP sensor) to calculate the approximate amount of air the engine in your pickup (car, van, or SUV) is breathing.
• That your vehicle does NOT use a mass air flow (MAF) sensor (although some 1996+ vehicles do).

The PCM then uses both these inputs to calculate the correct amount of fuel the engine needs to run at its best.

Here are some more specifics when you turn the key and start the engine:

1. The wire labeled with the number 1 supplies 5 Volts DC to the MAP sensor. This voltage is supplied by the PCM.
2. The wire labeled with the number 3 supplies Ground to the MAP sensor. This Ground is supplied by the PCM.
3. As the engine starts and the pistons start to create vacuum.
4. This vacuum is supplied to the MAP sensor thru' a plastic vacuum line.
5. The MAP sensor now starts to measure the vacuum and sends this info to the PCM thru' the wire labeled with the number 2.
6. The PCM receives crankshaft RPM info from the Profile Ignition Pickup (PIP) inside the distributor (via the ignition control module).
7. As mentioned before, the PCM uses both the MAP sensor info and PIP signal input to calculate fuel injection.

The absolute best way to test the MAP sensor is to bench test it, and this is how I'm gonna' show you how to test it in this tutorial.

Where To Buy The MAP Sensor And Save

You can find the MAP sensor in any auto parts store. If you're wanting/needing to save a few bucks, then buying the MAP sensor online is the route to take.

The following links will help you comparison shop for the MAP sensor:

Will the above MAP sensor fit your particular Ford pickup (van or SUV)? Don't worry, once you get to the site they'll make sure it fits (by asking you the specifics of your particular vehicle). If it doesn't fit, they'll find you the right one.

TEST 1: Checking The MAP Sensor Signal

The very first thing that we're going to do is check the MAP sensors signal.

Specifically, we want to see if the MAP sensors Hertz frequency signal decreases as vacuum is applied to it and then increases as that vacuum is released.

If the MAP sensor is bad, then it's signal off a stock in one value no matter how much vacuum is applied/released to it.

IMPORTANT: You'll need a multimeter that can read Hertz frequency. Yeah, I know, this really sucks if you don't have one but this is the only way to bench test the Ford MAP sensor (if you need to buy one, check out my recommendation by clicking here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

Let's get testing:

1. 1

   Disconnect the vacuum line (or hose) that connects the MAP sensor to the intake manifold.

2. 2

   Now, connect your vacuum gauge to the MAP sensor using a vacuum hose.

3. 3

   Set your multimeter's selector in Hertz (Hz) mode.

4. 4

   Connect the red multimeter test lead to the MAP sensor's wire labeled with the number 2 in the image above.
   
   Remember, the MAP sensor on your Ford must remain connected to its 3 wire connector.

5. 5

   Connect the black multimeter test lead directly to the battery negative (-) terminal.

6. 6

   Turn the key on but DO NOT start the engine. This will power up the MAP sensor.

7. 7

   Your multimeter should register around 152 Hertz (Hz) with the key on and the engine off and without any vacuum applied to the MAP sensor.

8. 8

   Pump up the vacuum pump. You should see the MAP sensor's Hertz values decrease:
   
   1.) 0 in. Hg ...... 152 Hz.
   
   2.) 5 in. Hg ...... 141 Hz.
   
   3.) 10 in. Hg .... 127 Hz.
   
   4.) 15 in. Hg .... 115 Hz.
   
   5.) 20 in. Hg .... 101 Hz.
   
   Repeat this test step several times and each time, you should see always see that the Hertz reading should increase smoothly and without any skips or gaps in the readings.

OK, let's take a look at what your test results mean:

CASE 1: Your multimeter displayed a decreasing Hertz (Hz) reading as you applied more vacuum. This is the correct and expected test result and it lets you know that the manifold absolute pressure (MAP) sensor is OK. No further testing is required.

Now, if your vehicle still has the MAP sensor code lighting up the check engine light (CEL) on your instrument cluster, take a look at the section: MAP Sensor Code Won't Go Away for more info.

CASE 2: Your multimeter DID NOT display a decreasing Hertz (Hz) signal as you applied more vacuum. The next step is to make sure that the MAP sensor is getting power. Go to: TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts.

CASE 3: Your multimeter DID NOT register any Hertz reading. This usually means that the MAP sensor is fried but not always.

To be absolutely sure, the next step is to make sure the MAP sensor is getting power. Go to: TEST 2: Making Sure The MAP Sensor Is Getting 5 Volts.