Testing The Ignition System (1998-2003 3.9L Dodge Dakota)

TEST 2: Testing For Spark At The Distributor Cap

Spark plug wires don't last forever and sooner or later they're gonna' stop transmitting spark to their spark plugs.

The best way to test a spark plug wire is to test for spark directly on the distributor cap tower of the spark plug wire that did not spark in TEST 1.

If the spark tester sparks (while connected to the spark plug wire's distributor cap tower), then we can conclude that the spark plug wire is bad.

If the distributor cap tower does not spark, then you can conclude that the distributor cap is bad and needs to be replaced.

Let's get started:

1. 1

   Remove the spark plug wire (that did not spark) from its tower on the distributor cap.

2. 2

   Place the spark tester directly on the tower (see photo above).
   
   Use a small piece of vacuum hose to secure the spark tester to the metal terminal of the tower (the arrow in the photo points to the vacuum hose I'm using).

3. 3

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

4. 4

   Ask your helper to crank the engine while you observe the HEI spark tester.

5. 5

   The spark tester should spark.

6. 6

   Repeat this test on the other distributor cap towers that did not spark (if applicable).

Let's analyze your test results:

CASE 1: You got spark. This is the correct test result and it confirms that the spark plug wire (that did not spark in TEST 1) that connects to that tower is bad, replace all of the spark plug wires as a set.

Replacing the spark plug wires will solve your misfire condition. Now, if the rest of the distributor components (distributor cap and rotor) are as old as the spark plug wires then I recommend that you replace them too.

Here's why: As the spark plug wire gets older (they usually have a service life 3 to 4 years), its normal resistance to spark increases to the point that it can't and doesn't channel spark to the spark plug. This will either cause a misfire, or a lack of power, or a no-start condition.

CASE 2: You got NO spark. This test result confirms that the distributor cap is bad.

Replace the distributor cap and distributor rotor as a set. This should solve your misfire problem. Now, if the rest of the distributor components (spark plug wires and spark plugs) are as old as the distributor cap and rotor then I recommend that you replace them too.

Here's why: As the distributor cap ages, the terminals that transmit the spark to the spark plug wires corrode. This corrosion increases the resistance to spark and over time (as more corrosion is created) this same corrosion will stop the transmission of spark to the spark plug wires.

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

If you got a no spark test result in TEST 1, then the next step is to check the ignition coil's high tension wire for spark.

As shown in the photo above, this test simply involves disconnecting the ignition coil's high tension wire from the center of the distributor cap and attaching the spark tester to it.

If the spark tester sparks, then you can conclude that the no-spark test result you got in TEST 1 from all of the spark plug wires is due to a bad distributor rotor and cap.

If the spark tester does not spark, then the next step is to test for spark directly on the ignition coil (TEST 4).

These are the test steps:

1. 1

   Disconnect the high tension wire that connects to the center of the distributor cap.
   
   NOTE: The other end of the high tension wire must remain connected to the ignition coil.

2. 2

   Connect the spark tester to the ignition coil high tension wire (as shown in the photo above).
   
   NOTE: You'll connect the spark tester to the end of the wire that connects to the center tower of the distributor cap. The other end of the wire remains connected to the ignition coil.

3. 3

   Ground the spark tester to the battery negative (-) terminal with a battery jump start cable.

4. 4

   Have your helper crank the engine as you hold the HEI spark tester.

5. 5

   The spark tester should spark.

Let's analyze your test results:

CASE 1: The spark tester sparked. This is the correct test result.

This test result confirms that the distributor cap and rotor are bad (and need to be replaced) only if you have:

• Confirmed that all of the spark plug wires are not sparking (TEST 1).
• Confirmed that the ignition coil's high tension wire does spark (TEST 3).

Replacing the distributor cap and rotor as a set should solve the no-start problem on your 3.9L V6 Dodge Dakota.

CASE 2: The spark tester DID NOT spark. This tells you that the distributor is not getting spark.

Then the next step is to check for spark directly on the ignition coil's tower. For this test go to: TEST 4: Testing The Ignition Coil For Spark.