IGNITION COIL TEST 4: Testing The Switching Signal
In the previous test you confirmed that the ignition coil is being supplied with power (12 Volts DC), now, you need to see if the ignition coil is getting an activation signal, called the Switching signal, from the ignition control module (ICM).
This test is accomplished using a 12 Volt test light and is done while cranking the engine on your 2.9L, 3.0L, or 3.8L Ford car (or pick up, mini-van).
Alright, this is what you'll need to do:
Reconnect the high tension wire to the ignition coil and the distributor cap, if you haven't done so.
Probe the wire labeled with the number 2 in the image above with the test light's metal probe and.
Connect the test light's crocodile type connector to your Ford's battery positive post.
The ignition coil can be connected to its electrical connector or not.
When ready, have your helper crank the engine while you observe and hold the test light in place.
Your 12 Volt test light will either:
1.) Flash ON and OFF the whole time the engine is cranking.
2.) No flashing ON and OFF.
OK, let's take a look at what your results mean:
CASE 1: The test light flashed ON and OFF. This is means that the ignition control module is activating the ignition coil and since the ignition coil is not sparking, the ignition coil is bad. Replace the ignition coil.
Here's why: If the ignition coil is getting power (12 Volts) and is getting the Switching signal, it HAS TO SPARK, since it isn't, this tells you that it's fried.
CASE 2: The test light DID NOT flash ON and OFF. This test result exonerates the ignition coil, since without this Switching signal, it won't spark.
The most likely cause of this missing Switching signal is either a bad ignition control module (ICM) or a bad Profile Ignition Pickup (PIP) sensor (which is Ford's fancy name for the crankshaft position sensor). I have written an article that will help you to test both of these at:
1.) If your Ford vehicle has the ignition control module mounted on the distributor, go to: Ford Distributor Mounted Ignition Module & PIP Sensor Test (this article is found at easyautodiagnostics.com).
2.) If your Ford vehicle has the ignition control module mounted on the Fender, go to: Ford Fender Mounted Ignition Module & PIP Sensor Test (this article is found at easyautodiagnostics.com).
How Does The Ignition Coil Work?
When you turn the key and start cranking the engine, this is what happens (in a nutshell, that is):
- The ignition control module (ICM) and the ignition coil get power (12 Volts).
- Power is fed to the ignition coil thru' the wire labeled with the number 1.
- The Profile Ignition Pickup (PIP) sensor (also known as the crank sensor), gets power from the ICM and:
- Starts to generate a crankshaft position signal (called the PIP signal) that is received by the ignition control module (ICM).
- When the ICM gets the PIP signal, it starts to switch the ignition coil ON and OFF by interrupting the ignition coil's primary voltage.
- This ON and OFF action is called the Switching signal throughout the article.
- The ignition coil gets this Switching signal on the wire labeled with the number 2.
- Once the ignition coil gets this Switching signal, it starts to spark.
- This spark is delivered to the center of the distributor cap by a high tension wire.
- Once the distributor gets this spark, it distributes it to all six cylinders.
- By this time, the PCM is also injecting fuel into the engine cylinders, which causes your Ford to start.
Pretty simple stuff!