TEST 3: Testing The Ignition Coil's High Tension Wire

How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04)

OK, in this step you'll test the spark plug wire (high tension wire) that feeds the spark to the distributor (from the ignition coil) to see if it is BAD or if the distributor cap is BAD and the cause of your No-Spark/No-Start Condition.

  1. Disconnect the ignition coil's high tension wire that plugs into the distributor cap (as shown in the photo). The other end has to stay plugged to the ignition coil.
  2. Now, connect the HEI spark tester to the end of the high tension wire that you just disconnected from the distributor cap with a small piece of vacuum hose.
  3. Now, ground the HEI spark tester with the same battery jump start cable you have been using for the previous tests.
  4. When all is ready, have your helper crank the engine.
  5. As before, observe the HEI spark tester to see if spark jumps across its air gap.

You'll get one of the 2 results: (1) Spark or (2) No Spark. Let's analyze each result in more detail below:

CASE 1: If the spark tester sparked, this result confirms that the ignition coil's high tension wire is good and that the ignition coil itself is also good. By a process of elimination these tests confirm that the distributor cap is BAD. Replace the distributor cap and rotor as a set and your no start condition should be solved.

CASE 2: If the spark tester DID NOT spark. Then further testing is required to see if the problem is due to a BAD ignition control module (ICM), BAD ignition coil, BAD pick up coil or something else. We're gonna' find out with the rest of the tests, go to: TEST 4: Spark Test At Ignition Coil Tower.

TEST 4: Spark Test At Ignition Coil Tower

How To Test A Misfire / No Spark-No Start Condition (4.3L, 5.0L, 5.7L 96-04)

So far, in all of your tests, you have gotten a No spark result on everything you have tested. Now, you're gonna' test for spark directly on the ignition coil's tower.

  1. Remove the spark plug wire that's attached to the ignition coil's tower (as shown in the photo on the left).
  2. Now, connect the HEI spark tester to the coil's tower with a small piece of vacuum Tubing (this is important!, look at the photo to see how I've done it).
  3. With the HEI spark tester being held in place on the coil with a battery jump start cable (who's other end is grounded on the engine or battery negative post), ask your helper to crank the engine once again while you watch for spark jumping across the air gap of the spark tester.

You're gonna' get one of the 2 results: (1) Spark or (2) No Spark. Let's analyze each result in more detail below:

CASE 1: If you got spark, then the spark plug wire that feeds the distributor cap spark is BAD and the ignition coil is GOOD. Replace the spark plug wire by replacing All of the spark plug wires.

Here's why: As the spark plug wire ages, its normal resistance to spark increases to the point that the wire can not and does not transmit the spark to the spark plug. This will either cause a misfire, or a lack of power, or a no start condition. The spark plug wires don't last forever, especially after-market ones (average life-span is 3 to 4 years)

CASE 2: If you got NO spark. Then further testing is required to see if the problem is due to a BAD ignition control module (ICM), BAD pick up coil or something else. We're gonna' find out with the rest of the tests, go to: TEST 5: Testing The Ignition Coil For 12 Volts.