How To Test The Ignition Coil (Ford 2.9L, 3.0L, 3.8L)

When the ignition coil on your 2.9L, 3.0L or 3.8L Ford V6 goes bad, your Ford is not gonna' start and you might be left wondering if the problem is the ignition coil or the ignition control module. Well, in this article, I'm gonna' show you a very easy but very accurate way to find out if the ignition coil is bad or not.

The test that you're gonna' learn in this article is an on-car test of the ignition coil done (in part) with the engine cranking. You won't be measuring the resistance of the ignition coil's Primary or Secondary circuits. No sir, in my opinion this test (the Primary/Secondary resistance test) is a complete waste of time and life that does not work around 99% of the time to diagnose a bad ignition coil.

Symptoms Of A Bad Ignition Coil

The most obvious symptom of a bad ignition coil on your 2.9L, 3.0L, 3.8L Ford car, mini-van, or pickup is a no-start no-spark condition.

Here are some more specific symptoms of a bad coil:

1. The PCM (Powertrain Control Module = Fuel Injection Computer) will still pulse the fuel injectors.
   • This means that if you do a Noid light test, the Noid light will flash ON and OFF.
   • And if the Noid light flashes ON and OFF, this indirectly tells you that the crank sensor is good.
2. The PCM will still activate the fuel pump.
   • This can easily be checked by hooking up a fuel pressure gauge to the Schrader valve (on the fuel injector rail) and checking the fuel pressure to see if it's at specification.
3. The starter motor will still crank the engine since the ignition coil circuits don't have anything to do with the starter motor circuits.

It's too bad the PCM is too dumb to find out that the ignition coil has failed (and thus the cause of the no-start condition) but it's really not necessary, since the ignition coil test is a pretty easy one to do and the accompanying symptoms (of a failed coil) are easy to observe and/or test.

IGNITION COIL TEST 1: Testing The Spark Plug Wire

Even if you have already verified that you have a bonafide no-spark condition on your Ford car (pick up or mini-van) you need to start your ignition coil troubleshooting and tests here.

You'll notice that I'll be asking you to use an HEI spark tester for the spark test and you may be wondering if you can use any other type of spark tester and the answer is yes you can. The biggest reason I recommend the HEI spark tester is that it is a very, very accurate spark tester and you can buy it here: OTC 6589 Electronic Ignition Spark Tester (Amazon affiliate link).

The very first thing that you need to do is make sure that the ignition coil's high tension wire (the one that feeds the coil's spark to the distributor cap) is good or bad and this is what you'll need to do:

1. 1

   Disconnect the ignition coil's high tension wire from the distributor cap only but leave the other end connected to the ignition coil's tower.

2. 2

   Now, on the end that you just unplugged from the center of the distributor cap, Attach the HEI spark tester (see photo above).

3. 3

   Using a battery jump start cable, Ground the HEI spark tester to the battery negative (-) terminal.

4. 4

   When you've finished setting up the spark tester, have your helper crank the engine (while you observe the spark tester at a safe distance).

5. 5

   You'll get one of two results from the HEI spark tester: spark or no spark.

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

CASE 1: You got spark. This means that the ignition coil and its high tension wire are good. The cause of the no-start on your 2.9L, 3.0L, or 3.8L Ford car (or pick up, mini-van) is not due to a bad ignition coil.

CASE 2: You got NO spark:. This test result doesn't condemn the ignition coil or the high tension wire to the trash just yet. The wire could be bad or the ignition coil could not be receiving its switching signal from the ignition control module (ICM) or the coil could really be fried. The next step will help you to find out, go to: IGNITION COIL TEST 2: Testing For Spark Directly On The Ignition Coil Tower

IGNITION COIL TEST 2: Testing For Spark Directly On The Ignition Coil Tower

One of the most common types of failures that'll keep your car from starting is the ignition coil wire going bad.

To eliminate this possibility, in this test step, you're gonna' test for spark directly on the ignition coil.

The result of this spark test will let you know if the high tension cable (that transmits the spark from the ignition coil do the distributor cap) is bad and not letting spark thru' to the distributor cap.

Or the spark test will let you know that you need to continue to the next test.

Alright, this is what you'll need to do:

1. 1

   OK, disconnect the high tension wire from the ignition coil.

2. 2

   Now, connect the HEI spark tester to the ignition coil's tower using a small piece of vacuum hose. This is important, see how I've done it in the photo above.

3. 3

   Now Ground the spark tester using a battery jump start cable directly on the battery negative (-) terminal.

4. 4

   When ready have your helper crank the engine as you eyeball the HEI spark tester, you'll see one of two results: spark or no spark.

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

CASE 1: You got spark. This spark test result tells you that the high tension wire is FRIED and is the cause of your no-start condition. Replace all of the spark plug wires as a set.

CASE 2: You got NO spark:. This spark test result eliminates the high tension wire and means you're getting closer to the actual cause of the ignition coil's no-spark condition.

The next step is to verify that the ignition control module (ICM) is activating the ignition coil. For this test, go to: IGNITION COIL TEST 3: Checking For 12 Volts.

IGNITION COIL TEST 3: Checking For 12 Volts

So far, you have verified that you do have a bonafide no spark situation coming directly from the ignition coil, the next couple of tests are to test the ignition coil itself.

OK, before we start (and to help you make sense of this test and the next one) you're aware that the ignition coil needs power in the form of 12 Volts and that it needs a Switching signal to create spark. Well, in this test step, you'll check for these 12 Volts either using a multimeter or a 12 Volts DC test light.

Alright, this is what you'll need to do:

1. 1

   With your multimeter still in Volts DC mode from the previous test and the key ON (but engine OFF).

2. 2

   Probe the wire labeled with the number 1 in the image above, with the red multimeter test lead.

3. 3

   Now Ground the black multimeter test lead on the battery's negative (-) post.

4. 4

   Your multimeter should show you either: 1.) 12 Volts DC or 2.) 0 Volts.

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

CASE 1: The multimeter registered 12 Volts. This is the correct result and tells you that the next step is to check that the ignition coil is getting a switching signal from the ignition control module (ICM). Go to: IGNITION COIL TEST 4: Testing The Switching Signal.

CASE 2: The multimeter DID NOT register 12 Volts. Double check your multimeter connections and repeat the test. If your multimeter results still do not indicate 12 Volts, then the ignition control module (ICM) is not fried and not the cause of the no-spark no-start problem, since without power, it won't work.

Although it's beyond the scope of this article to find the cause of these missing 12 Volts, resolving this issue will solve the no-spark no-start issue.

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:

1. 1

   Reconnect the high tension wire to the ignition coil and the distributor cap, if you haven't done so.

2. 2

   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.

3. 3

   When ready, have your helper crank the engine while you observe and hold the test light in place.

4. 4

   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):

1. 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.
2. 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).
3. 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.
4. 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.
5. By this time, the PCM is also injecting fuel into the engine cylinders, which causes your Ford to start.

Pretty simple stuff!

Related Test Articles

I've written several more tutorials that may be of interest to you. These are specific 3.0L, 3.8L Ford car (pick up, van) tutorials you can find here: Ford 3.0L, 3.8L Index Of Articles.

If you need a complete ignition system test article I recommend two I have written and located at easyautodiagnostics. Com:

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).