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: Hertz enabled Multimeter -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)... or you can use the ‘good ole lungs’, but I'll leave this up to you.
To help you navigate this article a little easier, here are its contents at a quick glance:
- Symptoms of a BAD MAP Sensor.
- What Does the MAP Sensor Do?
- TEST 1: Checking the MAP Sensor Signal.
- TEST 2: Checking the 5 Volt Power Signal.
- TEST 3: Checking the MAP Sensor Ground.
- MAP Sensor Code Won't Go Away.
- Where to Buy the MAP Sensor and Save.
- More Ford 4.9L, 5.0L, 5.8L Tutorials.
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 and...
- Then sends this info 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...