In this article, I'm gonna' show you a simple but very accurate way of testing the manifold absolute pressure (MAP) sensor on your 4.9L, 5.0L, or 5.8L Ford car (pick up, van).
As you may already be aware, the Ford MAP sensor does not produce a MAP signal that can be measured in Volts DC. 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 -at: easyautodiagnostics.com).
One more thing, this test involves using a vacuum pump, that you can rent at your local auto parts store (AutoZone, O'Reilly Auto Parts) or you can use the ‘good ole lungs’, but I'll leave this up to you.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar El Sensor MAP De Ford (4.9L, 5.0L, 5.8L) (at: autotecnico-online.com).
Symptoms Of A Bad MAP Sensor
When the manifold absolute pressure (MAP) sensor goes bad, you'll get a failed MAP sensor diagnostic trouble code.
- 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.
- 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.
The manifold absolute pressure (MAP) sensor is one of the most critical sensors the PCM (Powertrain Control Module = Fuel Injection Computer) needs to give the engine in your car, pickup, van or SUV running optimally and so, when the MAP sensor fails, you'll get some hard symptoms.
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:
- The PCM supplies voltage the MAP, in the form of 5 Volts on the wire labeled with the number 1.
- The PCM supplies Ground to the MAP on the wire labeled with the number 3.
- As the engine starts and the pistons start to create vacuum.
- This vacuum is supplied to the MAP sensor thru' a plastic vacuum line.
- The MAP sensor now starts to measure the vacuum.
- This vacuum measurement info is then sent to the PCM thru' the wire labeled with the number 1.
- The PCM receives crankshaft RPM info from the Profile Ignition Pickup (PIP) inside the distributor (via the ignition control module).
- 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 article. Let's turn the page and get testing.
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 manifold absolute pressure (MAP) sensor's job is to measure the amount of vacuum inside the intake manifold and convert this measurement into a Hertz frequency signal that it sends to the Powertrain Control Module (PCM= Fuel Injection Computer).
To get this show on the road, the very first thing that you'll do, is to see (with a multimeter) if the MAP sensor is able to create a good MAP signal. This is done using a vacuum pump while the MAP sensor is still connected electrically to the vehicle.
At the bottom of the article I have included the three different possible results you'll obtain from this test and how to interpret them.
OK, this is what you need to do:
Disconnect the vacuum line (or hose) that connects the MAP sensor to the intake manifold.
Now, connect your vacuum gauge to the MAP sensor using a vacuum hose.
Set your multimeter's selector in Hertz (Hz) mode and probe the MAP sensor's wire labeled with the number 2 in the image above.
Remember, the MAP sensor on your Ford pick up (or van or car) must remain connected to its 3 wire connector.
Connect the black multimeter test lead directly to the battery negative (-) terminal.
Turn the key ON but don't start the engine on your Ford car (or pick up or van). With the key ON, the MAP sensor will get power in the form of 5 Volts from the PCM (Powertrain Control Module= Fuel Injection Computer).
With the key ON and the engine OFF and without any vacuum applied to the MAP sensor, your multimeter should register around 152 Hertz (Hz).
Now, as you pump up the vacuum pump, the MAP sensor should make your multimeter register the following Hertz (Hz) values at the following vacuum values (they may differ a little on your specific Ford 4.9L, 5.0L, or 5.8L car, pick up, or van):
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 vacuum pump test and multimeter's test results mean:
CASE 1: Your multimeter displayed a decreasing Hertz (Hz) reading as you applied more vacuum. With this result you now know that the manifold absolute pressure (MAP) sensor on your Ford car (or pick up or van) is OK and not the cause of the problem or issue. 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. This confirms that the manifold absolute pressure (MAP) sensor on your Ford car (or pick up or van) is bad and needs to be replaced. Replacing the MAP sensor will solve the issue.
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, you'll need to test that the MAP sensor is getting power and Ground. If both (power and Ground) are present, the MAP sensor is bad. To test for power, go to: TEST 2: Checking The 5 Volt Power Signal.