TEST 2: Testing The Ignition Coil Tower For Spark
It's not uncommon for the ignition coil's high voltage wire to fail, stopping the transfer of spark from the ignition coil to the distributor cap.
You and I can indirectly test the ignition coil's high tension wire by checking for spark directly at the ignition coil tower.
If the ignition coil tower sparks, we can conclude that the high voltage wire is bad, since it didn't spark in TEST 1.
These are the test steps:
- 1
Disconnect the high tension wire from the ignition coil tower.
- 2
Attach the HEI spark tester to the ignition coil tower using a small piece of vacuum hose (see the illustration above).
NOTE: The vacuum hose must be short enough so that both the HEI spark tester and the ignition coil tower can make metal to metal contact. - 3
Connect the HEI spark tester to the battery negative (-) terminal using a battery jump start cable.
- 4
Have your helper crank the engine while you observe the spark tester from a safe distance.
- 5
You'll get one of two results:
1.) The spark tester will spark.
2.) The spark tester will NOT spark.
Let's take a look at what your test results mean:
CASE 1: The spark tester sparked. This test result tells you that the ignition coil high tension wire is defective and that it needs to be replaced.
Replace the entire set of high tension wires (also known as spark plug wires).
CASE 2: The spark tester DID NOT spark. This test result eliminates the high tension wire as being defective.
The next step is to check that the ignition coil is getting power. Go to: TEST 3: Making Sure The Ignition Coil Is Getting Power.
TEST 3: Making Sure The Ignition Coil Is Getting Power
The ignition coil requires 12 Volts to produce a spark. So for our third test, we'll check that it is receiving 10 to 12 Volts.
The wire that supplies 12 Volts to the ignition coil is the pink (PNK) wire of the gray connector and connects to the male spade terminal marked with the letter B in the illustration above.
We'll run a simple multimeter voltage test to verify that 12 Volts are present on the PNK wire of the gray connector.
Let's begin:
- 1
Disconnect both ignition coil connectors from the ignition coil.
- 2
Place your multimeter Volts DC mode.
- 3
Connect the black multimeter test lead to the battery negative (-) post.
- 4
Turn the key to the ON position but don't start the engine.
- 5
With the red multimeter test lead, probe the male spade terminal of the gray connector that connects to the pink (PNK) wire.
- 6
Your multimeter should now read 10 to 12 Volts DC.
Let's take a look at your test results:
CASE 1: 10 to 12 Volts are present in the pink wire. This test result tells you that the ignition coil is getting 12 Volts.
Your next step is to make sure that the ignition control module (ICM) is activating the ignition coil. Go to: TEST 4: Making Sure The Ignition Coil Is Getting the Activation Signal.
CASE 2: 10 to 12 Volts are NOT present in the pink wire. This test results let you know that the reason that the ignition coil is not sparking is due to a lack of 12 Volts.
Your next step is to find out why these 12 Volts are missing. Once you restore these 12 Volts back to the ignition coil, you should get spark (and the engine started).
TEST 4: Making Sure The Ignition Coil Is Getting The Activation Signal
If you've reached this fourth test, you have confirmed the following:
- The ignition coil high tension wire does not spark (TEST 1).
- The ignition coil tower does not spark (TEST 2).
- The ignition coil is receiving 10 to 12 Volts (TEST 3).
For our final test, we'll verify that the ignition coil is receiving an enable signal (IC control signal) from the ignition control module (ICM).
The wire that provides this activation signal is the white (WHT) wire of the black connector.
To verify the presence of the 12 Volts IC control signal on the WHT wire, we'll use a 12 Volts automotive test light.
NOTE: This test is done with both the black and gray connectors connected to the ignition coil.
Alright, let's start:
- 1
Connect the test light's crocodile type connector to the battery positive (+) terminal.
- 2
Connect the metal point of the 12 Volt test light to the white (WHT) wire of the black connector.
The WHT wire connects to the terminal labeled with the letter C in the illustration above.
The WHT wire connects directly to the ignition control module and the is the one that delivers the ignition coil activation signal. - 3
Have your helper crank the engine while you observe the 12 Volt test light.
- 4
You'll see one of two things:
1.) The 12 Volt test light flashes ON and OFF.
2.) The 12 Volt test light DOES NOT flash ON and OFF
Let's take a look at your test results:
CASE 1: The 12 Volt test light flashed ON and OFF. This test result confirms that the ignition control module is creating and delivering an activation signal to the ignition coil.
You can conclude that the ignition coil is bad and needs replacement if you have:
- Confirmed that the ignition coil high tension wire does not spark (TEST 1).
- Confirmed that the ignition coil tower does not spark (TEST 2).
- Confirmed that the ignition coil is receiving 10 to 12 Volts (TEST 3).
- Confirmed that the ignition control module is creating and delivering an activation signal to the ignition coil (this test section).
CASE 1: The 12 Volt test light DID NOT flash ON and OFF. This test result tells you that the ignition control module is not activating the ignition coil.
This test result exonerates the ignition coil, since without this activation signal, it won't spark.
This missing activation signal is usually caused by one of the following issues:
- The ignition control module (ICM) has failed.
- The distributor pick-up coil has failed.
The following tutorial will help you test them:
More 2.5L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials
You can find a complete list of 2.5L Chevy S10 pickup, GMC S15 pickup, And GMC Sonoma tutorials here:
Here's a sample of the tutorials you'll find in the index:
- How To Test Engine Compression (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test For A Blown Head Gasket (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The TPS (1987-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
- How To Test The MAP Sensor (1985-1993 2.5L Chevrolet S10, GMC S15, GMC Sonoma).
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