How To Test The Ignition Coil And Power Transistor (1993-1998 3.0L Nissan Quest)

TEST 1: Testing For Spark At The Spark Plug Wires

The very first thing that we're going to do, to get our ignition system diagnostic underway, is to test for spark at all six spark plug wires.

To get the most accurate test result from your diagnostic you need to use a dedicated spark tester.

Any other method, that tests for spark without a spark tester, can give you a false test result that might call for you to replace parts that don't need to be replaced. Not to mention the time and money that will be wasted.

Spark testers are not expensive and if you need to buy one check out my recommendation here: HEI Spark Tester (at: easyautodiagnostics.com).

Now if you have already checked and have confirmed that none of the spark plug wires are sparking, then your starting point is: TEST 3: Testing The Ignition Coil's High Tension Wire For Spark.

These are the test steps:

1. 1

   Disconnect the spark plug wire from its spark plug.

2. 2

   Attach the HEI spark tester to the spark plug wire (see the photo above).

3. 3

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

4. 4

   Have your assistant crank the engine while you observe the spark tester. If you're testing a misfire condition, the engine will start so be careful.

5. 5

   You're going to see only one of two results: the spark tester will spark or it won't spark.

6. 6

   Repeat the spark test on the remaining spark plug wires.

Let's take a look at your test results:

CASE 1: All spark plug wires have spark. This is the correct and expected test result.

This result lets you know that the power transistor, ignition coil, camshaft position sensor, distributor rotor and cap, and spark plug wires are OK.

If your Nissan's 3.0L V6 engine is misfiring, take a look at the suggestions found here: Other Causes Of A Misfire.

CASE 2: All spark plug wires have NO spark. The next step is to check that the ignition coil's high tension wire is delivering spark to the distributor cap.

For this test go to: TEST 3: Testing The Ignition Coil's High Tension Wire For Spark.

CASE 3: Some but not all of the spark plug wires sparked. The next step is check for spark directly on the distributor cap towers that feed spark to the wires that did not fire off spark. For this test go to: TEST 2: Testing For Spark At The Distributor Cap.

TEST 2: Testing For Spark At The Distributor Cap

NOTE: This test step only applies if some of the spark plug wires DID NOT spark in TEST 1.

If in TEST 1 you had one or more spark plug wires that did not spark then our next test is to check for spark directly on the distributor cap (see photo above).

We're going to place the spark tester on the distributor cap tower of the spark plug wire that did not spark (in TEST 1).

If the spark tester sparks then you can conclude that the spark plug wire (that did not spark TEST 1) is bad and that you need to replace all of the spark plug wires.

If the spark tester DOES NOT spark then you can conclude that the distributor cap is bad and needs to be replaced.

Now, if you have already made sure that there is no spark from any of the six spark plug wires, then your starting point is TEST 3: Testing The Ignition Coil's High Tension Wire For Spark.

These are the test steps:

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).

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

In this test section we're going to make sure that the ignition coil's high-tension wire is delivering spark to the distributor cap.

It's not uncommon for the ignition coil's high-tension wire to fail. When this happens the distributor cap no longer gets spark from the ignition coil.

As you can see in the photo, we're going to connect the spark tester to the end of the high tension wire that connects to the distributor cap.

There's a good chance that you may need to use a piece of black electrical tape to hold the spark tester in place on the high tension wire's terminal as the engine is cranked.

NOTE: You may need to use a small piece of electrical tape to secure the spark tester to the high tension wire's metal terminal. In the photo above I'm not using any black electrical tape to secure the spark tester to the terminal.

Let's get testing:

1. 1

   Disconnect the high tension wire that connects to the center tower of the distributor.
   
   This high tension wire is the one that connects to the ignition coil.

2. 2

   Place the HEI spark tester directly on the ignition coil high tension wire's metal terminal (see the photo above).
   
   You may need to use a small piece of black electrical tape to secure the spark tester to the wire's metal terminal.
   
   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

   Connect 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 above the engine.

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 conclude that the distributor cap is bad 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 3.0L Nissan Quest (Mercury Villager).

CASE 2: The spark tester DID NOT 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.