How To Test The Ignition Coil (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma)

TEST 2: Testing For Spark Directly On The Coil Tower

If you've reached this section, you've checked and confirmed that there's no spark coming from the ignition coil high tension wire.

Now we'll test for spark directly at the ignition coil tower. To accomplish this, you can attach the spark tester to the ignition coil tower with a small piece of vacuum hose.

This small piece of vacuum hose will keep the spark tester in place and help transfer the spark from the coil tower to the spark tester (see the illustrations in the image viewer above).

If the spark tester sparks, you can definitely conclude that the high tension cable is defective. This defective spark plug wire is the reason why your vehicle will not start.

However, if the coil tower does not spark, you can rule out the high tension wire as defective and now focus on the ignition coil itself.

Alright, these are the test steps:

1. 1

   Remove the high tension wire from the ignition coil's tower.

2. 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's tower can make metal to metal contact.

3. 3

   Connect the HEI spark tester to the battery's negative (-) terminal with a battery jump start cable.

4. 4

   Have your helper crank the engine when the HEI tester has been set up.

5. 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 is the correct test result and it tells you two important things:

• The ignition coil is functioning and therefore not bad.
• The ignition coil's high tension wire is defective.

You should replace the entire set of high tension wires (also known as spark plug wires). As mentioned before, a high tension wire does that does not transmit spark is a very common problem as the spark plug wires start to age.

CASE 2: You got a NO spark test result. This test result eliminates the high tension wire itself as being defective.

Now we need to make sure that the ignition coil is getting 12 Volts and an activation signal from the ignition control module (ICM).

These two tests are very easy to perform. For now, let's move on to the next test which will test for 12 Volts. Go to: TEST 3: Making Sure The Ignition Coil Is Getting 12 Volts.

TEST 3: Making Sure The Ignition Coil Is Getting 12 Volts

OK, so far you've verified that the ignition coil tower is not sparking. This non-spark condition could be due to one of two things. Either the ignition coil is not getting 12 Volts or the activation signal is missing.

In this test section, we'll check that the ignition coil is getting 10 to 12 Volts DC from the pink (PNK) wire of the gray connector (the ignition coil has two connectors, one black and one gray).

In the photo above, I've marked the the pink (PNK) wire of the gray connector with the letter B.

You can use a 12 Volt test light or to get a more accurate reading, I suggest you use a multimeter. The instructions below assume that you're using a multimeter.

If you don't have a multimeter and need to buy one, check out my recommendations here: Buying A Digital Multimeter For Automotive Diagnostic Testing.

These are the test steps:

1. 1

   Disconnect both ignition coil connectors from the ignition coil.

2. 2

   Place your multimeter Volts DC mode.

3. 3

   Turn the key to the ON position but don't start the engine.

4. 4

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

5. 5

   With the red multimeter test lead, probe the male spade terminal marked with the letter B of the gray connector.

6. 6

   Your multimeter should now read 10 to 12 Volts DC.

Let's take a look at your test results:

CASE 1: Your multimeter indicates that power is present. 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.

This is a very simple test and I'll show you how to perform it step by step in the next test section. Go to: TEST 4: Making Sure The Ignition Coil Is Getting the Activation Signal.

CASE 2: Your multimeter indicates that power is missing. 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).

To further help you ignition coil troubleshooting efforts, you can find the ignition system circuit diagram here:

• 1991-1993 2.8L Chevy S10 Ignition System Circuit Diagram.

TEST 4: Making Sure The Ignition Coil Is Getting An Activation Signal

You've reached this point because you have confirmed that the ignition coil tower is not sparking and that it is getting 10 to 12 Volts.

Now we're gonna see if the ignition control module (ICM) is activating the ignition coil to spark. This is a pretty easy test that's done with a 12 Volt automotive test light.

What we'll do is connect the 12 Volt test light to the ignition coil's signal wire and crank the engine.

If the ignition control module (ICM) is activating the ignition coil, the 12 Volts test light will flash ON and OFF (when your helper cranks the engine).

But if the ignition control module isn't providing an activation signal, the 12 Volts test light will not flash ON and OFF while the engine is cranking.

NOTE: This test is done with both the black and gray connectors connected to the ignition coil.

Alright, let's get this party started:

1. 1

   With the 12 Volt test light, probe the white wire of the black connector.
   
   This is the wire identified the with the letter C in the image above.
   
   This wire connects directly to the ignition control module and the is the one that carries the ignition coil's activation signal.

2. 2

   Connect the test light's crocodile type connector to the positive (+) battery terminal.

3. 3

   Have your helper crank the engine while you observe the test light.

4. 4

   The 12 Volt test light should blink ON and OFF when cranking the engine if the ignition control module is activating the ignition coil.
   
   If the ICM is not activating the ignition coil, the 12 Volt test light will 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 as your helper cranked the engine. This is the correct test result and confirms that the ignition control module is activating 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 is not sparking (TEST 1).
• Confirmed that the ignition coil tower is not sparking (TEST 2).
• Confirmed that the ignition coil tower is getting 10 to 12 Volts (TEST 3).
• Confirmed in this test section that the ignition coil tower is getting an activation signal from the ICM.

If you'd like to save a few bucks buying the ignition coil (and factory original AC Delco ignition components), take a look at the following section: Where To Buy The Ignition Coil And Save.

CASE 1: The 12 Volt test light DID NOT flash ON and OFF as your helper cranked the engine. 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.

The most likely cause of this missing activation signal is either a bad ignition control module (ICM) or a bad distributor pickup coil (which is the system's CKP sensor).

I've written the following tutorial to help you test both of these components:

• How To Test The Ignition Control Module (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).

More 2.8L Chevy S10 Pickup, GMC S15 Pickup, And GMC Sonoma Tutorials

You can find a complete list of tutorials for the 2.8L V6 Chevrolet S10 pickup, GMC S15 pickup, and GMC Sonoma in this index:

• GM 2.8L Index Of Articles.

Here's a sample of the articles, you'll find in the Index of Articles:

• How To Test The Fuel Pump (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test Engine Compression (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test The EGR Valve (1988-1993 2.8L Chevrolet S10 Pickup, GMC S15 Pickup, GMC Sonoma).
• How To Test The Starter Motor (1988-1993 2.8L V6 Chevrolet S10 Pickup, GMC S15 Pickup).