How To Test The Ignition Coil (1989-1991 3.9L V6 Dodge Ram Pickup)

When one of the components that make up the ignition system, on the 1989-1991 Dodge Ram pickup, fail you'll either have an engine no-start issue or a cylinder misfire problem on your hands.

Thankfully, testing the ignition system on your Dodge Ram pickup isn't difficult at all and you won't need any fancy or expensive tools to get it done, either!

In this tutorial, I'm gonna show you how to check the spark plug wires, distributor cap and rotor, and the ignition coil.

I'm also including the link to the step-by-step tutorial for testing the distributor pickup coil so you've got everything covered.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.9L V6 Dodge Ram 150 Pickup: 1989, 1990, 1991, 1992, 1993.
• 3.9L V6 Dodge Ram 250 Pickup: 1989, 1990, 1991, 1992, 1993.
• 3.9L V6 Dodge Ram 1500 Pickup: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001.
• 3.9L V6 Dodge Ram 2500 Pickup: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001.

IGNITION SYSTEM WIRING DIAGRAM:

• Ignition System Circuit Wiring Diagram (1989 3.9L V6 Dodge Ram Pickup).
• Ignition System Circuit Wiring Diagram (1990-1991 3.9L V6 Dodge Ram Pickup).

DISTRIBUTOR PICKUP COIL TESTS:

• How To Test The Distributor Pickup Coil (1989-1991 3.9L V6 Dodge Ram Pickup).

Ignition System Test Basics

The ignition system on the 1989–1991 Dodge Ram 3.9L V6 is an old-school, mechanical distributor design. It's made up of these key parts:

• Ignition coil: Builds up and sends out the high-voltage spark each cylinder needs to combust the air/fuel mixture.
• Distributor: A mechanical part that sends that spark to the right cylinder.
• Distributor pickup coil: It's both a crankshaft position (CKP) and camshaft position (CMP) sensor in one assembly.
• Spark plug wires (aka high tension wires): Carry the spark from the distributor to the spark plugs.
• Distributor cap and rotor: Team up to make sure the spark lands in the correct cylinder at the right time.

Here's what happens behind the scenes when you turn the key and crank the engine:

1. CMP/CKP signal: The pickup coil inside the distributor kicks off the CMP and CKP signal your pickup's fuel injection computer needs to know which cylinder piston is coming up on its Top Dead Center (TDC) position.
2. Ignition coil activation: Once the computer gets the pickup coil signal:
   • It turns on the ASD relay —which powers up the fuel pump, fuel injectors, and ignition coil with 12 Volts.
   • It triggers the ignition coil to create spark.
   • It activates the fuel injectors to spray fuel into the cylinders.
3. Spark goes to distributor: The spark travels through the ignition coil's high tension wire into the center of the distributor cap.
4. Rotor in action: Inside the cap, the rotor spins and sends that spark to the right terminal under the cap.
5. Spark hits spark plugs: From there, the spark moves through the plug wires and fires off at each spark plug.

In this tutorial, I'm gonna show you how to check the ignition coil's high tension wire, the spark plug wires, the distributor cap and rotor, and the ignition coil itself.

What Tools Do I Need To Test The Ignition System?

You'll need a few basic tools to test the ignition system on your V6 Dodge Ram pickup —and the good news is, none of them are expensive.

The one tool you'll definitely need is a spark tester. Here's what I recommend:

• HEI spark tester: This one's a must if you want accurate results. It shows you clearly whether spark's getting delivered or not. I use this exact one:
  • OTC 6589 Electronic Ignition Spark Tester (at: amazon.com).
• 12-volt test light: You'll need this to check if the ignition coil is getting its activation signal. Here's the one I use and trust:
  • Lisle 28400 Heavy Duty 12 Volt Test Light (at: amazon.com).
• Jumper cables: Just your regular battery booster cables will do the trick.
• Multimeter: If you don't already have one —or if you're thinking of upgrading— this is the meter I use and recommend:
  • Tekpower TP8268 AC/DC Auto/Manual Range Digital Multimeter (at: amazon.com).
• Spark plug wire pliers: These are a must-have for pulling wires off the plugs without tearing them up. If you don't have a pair, here's the one I suggest:
  • OEMTOOLS 25542 Spark Plug Pliers. (at: amazon.com).
• And last but not least —a helper. Trust me, having someone else crank the engine while you test makes the job way easier.

TEST 1: Testing The Spark Plug Wires For Spark

We're gonna start the ignition system check by testing for all 6 spark plug wires for spark —it's the first thing to rule out and the most important step. This is how we'll know if the engine no-start or misfire issue is coming from the ignition system.

I really want to emphasize this: Whether your Dodge Ram V6 cranks but won't start, or it runs rough and misfires, you've got to check for spark on all 6 spark plug wires.

Don't skip any wires. Testing every single one will give us a clear picture of what's going on and helps us avoid wasting time chasing the wrong problem.

NOTE: You'll need a proper spark tester for this. Any good-quality one will do the job, but if you're buying one, I strongly recommend the HEI spark tester —it's the one I trust. You can see what it looks like and buy one here: OTC 6589 Electronic Ignition Spark Tester (at: amazon.com).

CAUTION: You'll be cranking the engine during these tests, be careful and take all necessary safety precautions.

Alright, let's get started:

1. 1

   Disconnect the spark plug wire from cylinder #1.
   
   NOTE: Check image 2 of 2 to find the cylinder number layout.

2. 2

   Connect your HEI spark tester to that wire (see the photo above for reference).

3. 3

   Ground the spark tester using a jumper cable —clip the other end of the jumper cable to the battery's negative (-) post.

4. 4

   Have your helper crank the engine while you keep your eyes on the spark tester.
   
   NOTE: If you're tracking down a misfire, the engine might actually fire up —so be careful.

5. 5

   You'll see one of two results: Either you get spark, or you don't.

6. 6

   Do the same spark test on the rest of the plug wires, one at a time.

Now let's break down what your test results actually tell us:

CASE 1: All six spark plug wires are sparking. That's exactly what you're looking for.

This tells you the ignition coil, distributor cap and rotor, pickup coil inside the distributor, and all the plug wires are doing their job just fine.

If you're chasing a misfire on your 1989–1991 Dodge Ram V6, your next step is to look into these common causes: Other Causes Of A Misfire.

If you're dealing with an engine no-start issue, then a lack of spark isn't the problem —you've got to continue troubleshooting the issue by checking the fuel pump pressure, checking engine compression, etc.

CASE 2: None of the plug wires sparked. Next thing to check is whether the ignition coil's high tension wire is even sending spark to the distributor cap in the first place.

To test that, go here: TEST 3: Testing The Ignition Coil's High Tension Wire For Spark.

CASE 3: Some wires are sparking, others aren't. That usually points to one of two things: bad spark plug wires or a worn-out distributor cap.

We'll narrow it down by testing for spark right at the distributor towers that feed those dead wires. Go to: TEST 2: Testing For Spark At The Distributor Cap.

TEST 2: Testing For Spark At The Distributor Cap

There's a good chance the spark plug wire that didn’t spark in TEST 1 is doing so for one of two reasons:

• The distributor cap is bad.
• The spark plug wire itself is faulty.

To figure out which one it is, we’ll test for spark directly at the distributor cap tower that feeds the non-sparking wire.

Just like you see in the photo above —we'll unplug the non-sparking spark plug wire from its tower on the cap, and insert the spark tester directly into the tower.

If the tester sparks (while cranking the engine), we can conclude the spark plug wire is the problem and we need to replace all of them.

But if there's no spark coming out of the tower, then the distributor cap is bad and needs to be replaced.

Alright, here's how to run this test step by step:

1. 1

   Pull the spark plug wire off the tower on the distributor cap —the one that didn't spark in TEST 1.

2. 2

   Plug your spark tester straight into that tower (see the photo above).

3. 3

   Ground the spark tester using a jumper cable —connect the other end of the cable to the battery's negative (-) post.

4. 4

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

5. 5

   The spark tester should spark the whole time the engine is turning over.

6. 6

   If there are more spark plug wires that didn't spark in TEST 1, repeat this same process on each of their distributor cap towers.

Let's break down what your test results mean:

CASE 1: You saw spark at the tester. That's exactly what you're looking for —it confirms the spark plug wire connected to that tower is the problem. Time to toss the whole set and install new wires.

That should take care of the misfire (or engine no-start). And if your distributor cap and rotor are just as old, replace those too.

Here's why it matters: Spark plug wires don't last forever. As they age, their resistance goes up, and they stop carrying spark from the distributor cap to the spark plug. That leads to misfires or even an engine no-start issue.

CASE 2: No spark at all. That tells you the distributor cap is the problem —it's not passing spark through that tower like it's supposed to.

Installing a new distributor cap and rotor should solve the misfire (or engine no-start issue). If the spark plug wires and spark plugs have been around a while, it's a good idea to replace them too.

Here's why: The metal terminals inside the cap corrode and become pitted over time. That corrosion increases resistance, and eventually, it blocks the spark from reaching the wire, killing ignition to the cylinder completely.