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.
Contents of this tutorial:
- IGNITION COIL TEST 1: Testing The Spark Plug Wire.
- IGNITION COIL TEST 2: Testing For Spark Directly On The Ignition Coil Tower.
- IGNITION COIL TEST 3: Checking For 12 Volts.
- IGNITION COIL TEST 4: Testing The Switching Signal.
- How Does The Ignition Coil Work?
- Why The HEI Spark Tester.
- Related Test Articles.
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:
- 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.
- 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.
- 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 bona-fide 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. In the section Why The HEI Spark Tester, I go more in depth about this.
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:
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.
Now, on the end that you just unplugged from the center of the distributor cap, Attach the HEI spark tester (see photo in image viewer).
Using a battery jump start cable, Ground the HEI spark tester to the battery negative (-) terminal.
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).
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.