TEST 5: Testing The Ignition Coil For 12 Volts

Making Sure The Ignition Coil Is Getting 12 Volts. How To Test The GM Distributor Mounted Ignition Module

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 (12 Volts) because if it's not, you'll get a bona-fide No Spark No Start Condition.

For this test you can use a multimeter or a 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 Power Circuit feeds both.

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 (click here to see a picture of this tool). I don't recommend inserting anything into the front of the female terminal (the exception being TEST 7). Whatever method you use, the key here is not to damage the female terminal or the wire. Again, be careful. Use common sense and take all necessary safety precautions.

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

    Put 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 wire of the ignition coil connector (see photo above).

  3. 3

    With the black multimeter test lead probe the battery (-) negative terminal.

  4. 4

    Turn Key On with the Engine Off. You should see 12 Volts on the multimeter.

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

CASE 1: If you got 12 Volts. All is good in the neighborhood, 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 to kingdom come or until you turn off your engine.

CASE 2: If you DID NOT GET 12 Volts. You must find out why you're missing this voltage. Without this voltage the ignition control module nor the ignition coil will work. Resolving this power issue should solve your no start condition.

TEST 6: Verifying The Ignition Coil's Switching Signal

Verifying The Ignition Coil's Switching Signal. How To Test The GM Distributor Mounted Ignition Module

In this test you're gonna' verify that the ignition control module (ICM) is activating the ignition coil by verifying that the Switching Signal is present.

You're going to use an LED test tool. Click here for a picture of this tool and how to make it. Use an appropriate tool to pierce the wire. It's to this tool that you'll attach the LED to. Be careful and take all necessary safety precautions.

NOTE: This test is performed with the ignition coil and 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 wires of the ignition coil's connectors (see photo above).

  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. 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: If the LED flashed On and Off, then the ignition coil is bad, replace it. This also means that the ignition control module (ICM) and pick up coil are good. Replacing the ignition coil will solve your 'no spark no start' condition.

Here's why: The LED flashing On and Off confirms that the ignition module is activating the ignition coil. But since the ignition coil is bad, it's not sparking.

The only way that the ignition coil can produce this Switching Signal, is by receiving the pick up coil's signal.. therefore, you can deduce that the pick up coil is good too.

CASE 2: If the LED DID NOT flash ON and OFF. Re-check all of your connections and retry the test again. If still no light pulses on the test LED, go to: TEST 7: Testing The Pick Up Coil Signal.

Chevrolet Vehicles:

  • Astro 4.3L
    • 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • Blazer 4.3L, 5.0L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • Silverado C1500, C2500, C3500 4.3L, 5.0L, 5.7L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995

Chevrolet Vehicles:

  • Suburban C1500, C2500, C3500 5.7L, 7.4L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • Camaro 2.8L, 3.1L, 5.0L, 5.7L
    • 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992
  • Caprice Classic 4.3L, 5.0L, 5.7L
    • 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993

Chevrolet Vehicles:

  • Cavalier 2.0L, 2.8L
    • 1985, 1986
  • Celebrity 2.0L, 2.8L
    • 1985, 1986
  • El Camino 4.3L, 5.0L
    • 1985, 1986, 1987
  • G10 G20 G30 Van 4.3L, 5.0L, 5.7L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995

GMC Vehicles:

  • Sierra, Suburban C1500, C2500, C3500 4.3L, 5.0L, 5.7L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • G1500, G2500, G3500 4.3L, 5.0L, 5.7L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • Jimmy 4.3L, 5.0L, 5.7L
    • 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995

GMC Vehicles:

  • K1500, K2500, K3500 4.3L, 5.0L, 5.7L
    • 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995
  • S15 Jimmy 4.3L
    • 1988, 1989, 1990, 1991
  • Safari 4.3L
    • 1986, 1987, 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995

GMC Vehicles:

  • Sonoma 4.3L
    • 1991, 1992, 1993, 1994, 1995
  • Yukon 5.7L
    • 1992, 1993, 1994, 1995

Oldsmobile Vehicles:

  • Bravada 4.3L
    • 1991, 1992, 1993, 1994, 1995
  • Custom Cruiser 5.0L, 5.7L
    • 1991, 1992

Pontiac Vehicles:

  • Firebird 2.8L, 3.1L, 5.0L, 5.7L
    • 1985, 1986, 1987, 1988, 1989, 1990, 1991, 1992
  • Grand Prix 4.3L, 5.0L
    • 1986, 1987