How To Test The GM Distributor Mounted Ignition Module

TEST 5: Testing The Ignition Coil For 12 Volts

So far all of your tests (if you have started from TEST 1) indicate that you have no spark anywhere you've tested.

Everything seems to point to a bad ignition coil, and so in this test, we'll check that it's getting power (10 to 12 Volts) because if it's not, then your vehicle's engine is gonna' suffer a bonafide no spark no-start problem.

For this test you can use a multimeter or a 12 Volt automotive test light. Also, altho' you're testing the ignition coil for 12 Volts, you're indirectly testing the ignition module for 12 Volts also, since the same circuit feeds both with power.

The procedure I recommend to use (to accomplish all of the tests below) is to use a test probe that pierces thru' the wire's insulation (Wire Piercing Probe).

NOTE: This test is performed with the ignition coil and ignition control module connected to all of their connectors.

These are the test steps:

1. 1

   Place the multimeter in Volts DC mode.
   
   Don't have a digital multimeter? Need to buy one? Click here to see my recommendations: Buying A Digital Multimeter For Automotive Diagnostic Testing.

2. 2

   With the red multimeter test lead probe the pink (PNK) wire of the grey ignition coil connector.
   
   NOTE: The photo shows the PNK wire the black connector being pierced, I suggest you test the PNK wire of the grey connector.

3. 3

   Connect the black multimeter test lead to the battery negative (-) terminal.

4. 4

   Turn the key ON with the engine OFF.

5. 5

   You should see 10 to 12 Volts on the multimeter.

Let's take a look at what your test results mean:

CASE 1: You got 10 to 12 Volts. This is the correct and expected test result.

The next step is to check to see if the ignition coil is receiving the Switching signal from the ignition module. Go to: TEST 6: Verifying The Ignition Coil's Switching Signal.

In case you've forgotten, the Switching Signal is the signal that activates the ignition coil to start sparking away until you turn off your engine.

CASE 2: You DID NOT get 10 to 12 Volts. Without this voltage the ignition control module nor the ignition coil will work.

Your next step is to find out why this voltage is missing and resolve it. Resolving this power issue should solve your engine's no-start problem.

TEST 6: Verifying The Ignition Coil's Switching Signal

In this test, you're gonna' make sure that the ignition control module (ICM) is activating the ignition coil by verifying that it is producing a Switching signal.

To check for the presence of the Switching signal, we're going to use an LED light.

Since the ignition coil and the ignition module must remain connected to their electrical connectors, you'll need to use an appropriate tool to pierce the white wire of the ignition coil's black connector.

It's to this wire piercing tool that you'll attach the LED to (you can see an example of this tool here: Wire Piercing Probe). Be careful and take all necessary safety precautions.

IMPORTANT: This test is performed with the ignition coil and the ignition control module connected to all of their connectors.

OK, to get this show on the road, this is what you need to do:

1. 1

   Connect the black wire of the LED to one of the two white (WHT) wires of the ignition coil's connectors (see photo above).
   
   NOTE: The ignition coil and the ICM must remain connected to their electrical connectors for this test to work.

2. 2

   Connect red lead of LED to the battery positive (+) terminal. It is important that it be connected at the battery positive (+) terminal.

3. 3

   Have an assistant crank the engine.

4. 4

   The LED test tool should blink ON and OFF as the engine is being cranked.

Let's take a look at what your test results mean:

CASE 1: The LED flashed ON and OFF. This is the correct test result and lets you know that the ICM is producing the ignition coil's Switching Signal.

This test result confirms that the ignition coil is bad and needs to be replaced if you have:

• Confirmed that none of the spark plug wires are sparking (TEST 1).
• Confirmed that the ignition coil tower is not sparking (TEST 3 and TEST 4).
• Confirmed that the ignition coil and ICM are getting power (TEST 5).
• Confirmed that the ignition coil is getting its Switching signal.

Replacing the ignition coil to solve your vehicle' s no spark-no-start problem.

This test result also confirms that the ignition control module (ICM) and pick up coil are good.

CASE 2: The LED DID NOT flash ON and OFF. Re-check all of your connections and retry the test again.

If still no light pulses from the LED light, go to: TEST 7: Testing The Pick Up Coil Signal.