Ignition Coil And Basic Ignition System Tests (1990-1995 3.8L V6 Ford Taurus, Mercury Sable)

In this tutorial, I'm going to show you how to test the ignition system to see if it's causing a cylinder misfire or a no-start condition.

The specific components we'll be checking are the spark plug wires, distributor cap and rotor, and the ignition coil.

After you've done these basic tests, if you need to go further and check the ignition control module, I'll show you where to find that tutorial.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.8L V6 Ford Taurus: 1990, 1991, 1992, 1993, 1994, 1995.
• 3.8L V6 Mercury Sable: 1990, 1991, 1992, 1993, 1994, 1995.

RELATED IGNITION SYSTEM DIAGNOSTIC TESTS:

• How To Test The Ignition Control Module (1990-1995 3.8L V6 Ford Taurus, Mercury Sable).
• How To Test The PIP Sensor (1990-1995 3.8L V6 Ford Taurus, Mercury Sable).

IGN SYSTEM WIRING DIAGRAMS:

• Ignition System Wiring Diagram (1990 3.8L V6 Ford Taurus, Mercury Sable).
• Ignition System Wiring Diagram (1991 3.8L V6 Ford Taurus, Mercury Sable).
• Ignition System Wiring Diagram (1992-1995 3.8L V6 Ford Taurus, Mercury Sable).

Symptoms Of An Ignition System Fault

The ignition system on the 1990–1995 3.8L V6 Ford Taurus or Mercury Sable uses a mechanical distributor. For the most part, ignition system problems will cause one of two issues:

1. Engine cylinder misfires or a rough idle.
2. Engine no-start condition.

Now, since these vehicles are OBD I–equipped, you're not going to see any cylinder misfire diagnostic codes lighting up the check engine light (if the ignition system fault is causing a misfire). But what you'll see are one or more of the following performance symptoms:

• Rough or unstable idle.
• Lack of power under load or during acceleration.
• Engine hesitation or stumbling when you press the accelerator.
• Intermittent misfire at idle or while driving.
• Hard starting or extended cranking time.
• Poor fuel mileage.
• Occasional backfire through the intake or exhaust.

The cool thing is, with some basic tools, you and I can figure out exactly what's causing the cylinder misfire, rough idle, or engine no-start —if it's coming from one of the ignition system components (distributor cap, spark plug wires, ignition coil, etc.). And in this tutorial, I'm going to show you how to do that step by step.

What Tools Do I Need To Test The Ignition System?

To test the ignition system, you don't need any expensive diagnostic equipment, but you'll need a few basic tools, and these are:

• Spark tester: A dedicated spark tester is the most accurate way to check for spark. Any spark tester will do, but the one I use and recommend for its ease of use and accuracy is the OTC HEI Spark Tester. You can see an example of it here and purchase it here: OTC 6589 Electronic Ignition Spark Tester (Amazon affiliate link).
• 12V automotive test light: A regular 12V incandescent test light will help us check the ignition coil's activation signal in TEST 5. If you don't have one, this is the one I recommend —you can see it here: Lisle 28400 Heavy Duty 12 Volt Test Light (Amazon affiliate link).
• Multimeter: The multimeter will help us make sure the ignition coil's receiving battery power in TEST 4. If you don't have one, or if you're looking to upgrade, this is the one I use and recommend: Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (Amazon affiliate link).
• Spark plug wire puller: Spark plug wire pliers are almost a must-have tool for disconnecting the spark plug wires from the spark plugs. The main reason is that if you pull on the wire with your hand, the metal terminal inside the boot usually stays stuck on the spark plug. It can be reattached, but it's a hassle —and using spark plug wire pliers helps you avoid that altogether. These are the ones I recommend: Performance Tool W80519 Adjustable Spark Plug Boot And Wire Remover (Amazon affiliate link).

TEST 1: Checking For Spark At The Spark Plug Wires

To get our ignition system diagnostics started on your 3.8L V6 Ford Taurus or Mercury Sable, we'll begin by checking for spark at all six spark plug wires.

Before you start, I want to mention that you'll need to disconnect the spark plug wires from the spark plugs —and I highly recommend using spark plug wire pullers.

Pulling the high-tension wires off by hand usually results in the wire's metal terminal staying stuck on the spark plug. While you can reattach the terminal to the wire, it's a hassle you're better off avoiding by using the proper tool.

If you don't have spark plug wire pullers, these are the ones I use and recommend —and you can buy them here: Performance Tool W80519 Adjustable Spark Plug Boot And Wire Remover (Amazon affiliate link).

CAUTION: You'll be working around a cranking engine. Keep your hands, tools, loose clothing, and test leads clear of moving engine parts such as belts and pulleys. Secure any long hair and avoid leaning over the engine while performing the test. Always stay alert and aware of your surroundings when working near moving components.

Let's take it from the top:

1. 1

   Disconnect the spark plug wire from its spark plug.

2. 2

   Connect the spark plug wire to the spark tester.

3. 3

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

4. 4

   Have a helper crank the engine while you observe the spark tester.

5. 5

   You'll see one of two results: Spark or no spark.

6. 6

   Remove the spark tester and reconnect the spark plug wire to its spark plug.

7. 7

   Repeat steps 1 thru 6 on the remaining spark plug wires.

Let's interpret your spark test results:

CASE 1: All six spark plug wires are sparking. Awesome —this is the result we wanted to see. It tells us the ignition system's functioning correctly since it's delivering spark to all six spark plugs.

If your Ford Taurus or Mercury Sable still isn't starting, then the ignition system isn't behind the no-start —the problem lies elsewhere.

If you're troubleshooting a cylinder misfire or rough idle problem, you'll need to dig a little deeper. I recommend checking engine compression and testing the fuel injectors. Also, remove the spark plugs and check them for excessive wear or any other obvious issues.

CASE 2: You got spark from most, but not all, spark plug wires. This result tells you the ignition system's behind the cylinder misfire, rough idle, or no-start problem you're diagnosing.

Your next step is to check for spark directly on the distributor cap towers where those non-sparking spark plug wires connect. For this test, head over to: TEST 2: Checking For Spark At The Distributor Cap.

CASE 3: None of the spark plug wires are sparking. This result confirms that a lack of spark from the ignition system is what's keeping the engine from starting. Your next diagnostic step is to make sure the ignition coil's high-tension wire is delivering spark to the distributor cap. For this test, go to: TEST 3: Checking The Ignition Coil High Tension Wire For Spark.

TEST 2: Checking For Spark At The Distributor Cap

If you've reached this test section, it means you have one or more spark plug wires that didn't spark. This lack of spark is usually caused by one of two things:

• Either the spark plug itself is bad or...
• The distributor cap is bad.

The cool thing is, we can easily figure out which one's causing the no-spark result. All we have to do is check for spark directly at the distributor cap tower that the non-sparking spark plug wire connects to, using our spark tester.

Here's what we're looking for:

• Spark: This tells us the distributor cap tower's OK and the spark plug wire's toast.
• No spark: This tells us the distributor cap tower's bad and the cap needs to be replaced.

All right, let's get going.

1. 1

   Connect the spark plug wires to their respective spark plugs (if any are currently disconnected).

2. 2

   Disconnect the spark plug wire that did not spark from its tower on the distributor cap.
   
   NOTE: If you have multiple non-sparking spark plug wires, we'll test them one at a time. For this step, disconnect only one wire from its distributor cap tower. In Step 8, we'll move on to the next one.

3. 3

   Connect the spark tester to the distributor cap tower with a small piece of vacuum hose.
   
   In the photo above, the orange arrow points to the short piece of vacuum hose that is connecting the spark tester to the metal terminal of the distributor tower being tested.

4. 4

   Ground the spark tester on the battery negative (-) terminal using a battery jump start cable.
   
   NOTE: The battery jump start cable will also help you hold the spark tester in the distributor tower.

5. 5

   Have a helper crank the engine.
   
   CAUTION: The engine may start during this test. Take all necessary safety precautions and remain alert.

6. 6

   You'll get 1 of 2 results: Spark or no spark.

7. 7

   Remove the spark tester from the tower and reconnect the spark plug wire.

8. 8

   Repeat the test for any other distributor cap towers connected to non-sparking spark plug wires from TEST 1.

Here's what your test result is telling you:

CASE 1: The spark tester sparked. This is the correct test result, and it tells you that the distributor cap tower for the non-sparking spark plug wire is doing its job and transmitting spark to the wire.

Now, since the spark plug wire didn't spark in TEST 1, we can conclude that the wire itself is bad. Your next step is to replace all of the spark plug wires with a new set to fix the no-spark issue and solve the rough idle or cylinder misfire that this bad wire's causing.

CASE 2: The spark tester didn't spark. This result tells you the distributor cap itself is bad and needs to be replaced.

It's not uncommon for distributor cap towers to stop transmitting spark as the cap ages. To solve the issue, replace the distributor cap and rotor as a set. And if the spark plug wires are as old as the cap and rotor, replace them too.

TEST 3: Checking The Ignition Coil High Tension Wire For Spark

One of the most common issues with the 3.8L V6 ignition system is the high-tension wire that connects the ignition coil to the distributor eventually stops transmitting spark.

When this happens, the engine won't start because the distributor isn't receiving spark —and without spark, it can't distribute it to the six spark plugs.

The cool thing is, we can easily check if this is what's happening, and that's exactly what we're going to do in this test section.

We'll connect our spark tester to the ignition coil's high-tension wire and see if it sparks while we crank the engine.

Alright, let's get to it:

1. 1

   Disconnect the high tension wire from the center tower of the distributor cap.
   
   NOTE: Leave the other end of the high tension wire attached to the ignition coil.

2. 2

   Attach the HEI spark tester to the spark plug wire.

3. 3

   Connect the spark tester to the battery negative (-) post using a battery jump start cable (see the illustration above).

4. 4

   Have your helper crank the engine while you observe the spark tester from a safe distance.

5. 5

   You'll get one of two results:
   
   1.) The spark tester will spark.
   
   2.) The spark tester will NOT spark.

Let's examine your test result:

CASE 1: The spark tester sparked. This test result tells you several things:

• The high tension wire, ignition coil, ignition control module (ICM), and profile ignition pickup (PIP) sensor are all working correctly.
• The distributor cap and rotor are toast and need to be replaced.

Replace the distributor cap and rotor to get spark going to all six spark plug wires and solve the engine no-start problem.

CASE 2: The spark tester didn't spark. This result let's us know that the reason none of the spark plug wires sparked in TEST 1 is because the distributor cap isn't getting spark.

Our next diagnostic step is to check for spark directly at the ignition coil's tower (which will indirectly helps us find out if the high tension wire is OK or bad). For this test, go to: TEST 4: Checking The Ignition Coil Tower For Spark.