How To Test The Ignition System (1992-1997 3.9L Dodge Dakota)

TEST 2: Testing For Spark At The Distributor Cap

If one or several spark plug wires did not spark in TEST 1, then there's a good chance that this is due to:

• A bad distributor cap.
• Bad spark plug wires.

To find out, we're gonna' 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, then we can conclude that the spark plug wire is bad.

If the spark tester does not spark, then we can conclude that the distributor cap is bad.

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 lets you know that the spark plug wire that connects to that distributor cap tower is bad. Replace all of the spark plug wires with a new set.

The misfire problem you're troubleshooting should be resolved with a new set of spark plug wires. Now, if the distributor cap and rotor are as old as the spark plug wires, then I recommend that you replace them too.

Here's why: Spark plug wires usually have a service life 3 to 4 years. Eventually their normal resistance to spark will increase to the point that one or more spark plug wires will not transmit spark anymore. 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.

The misfire problem you're troubleshooting should be resolved with a new distributor cap and rotor. Now, if 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 confirmed that none of the spark plug wires are sparking (in TEST 1), then there's a good chance that the distributor cap is not getting spark.

So in this test section, we're gonna' make sure that the ignition coil's high tension wire is supplying spark to the distributor cap.

We'll accomplish this by connecting the spark tester to the ignition coil's high tension wire (the end that connects to the distributor cap) and testing it for spark. The photo above shows exactly how.

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 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.

You can correctly conclude 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 1992-1997 3.9L V6 Dodge Dakota.

If the spark plugs and the spark plug wires are as old as the distributor cap, I recommend you replace them too.

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.