TEST 1: Testing For Spark At The Spark Plug Wire
The best starting point, to diagnose a bad ignition coil pack on your Ford or Mercury vehicle is testing for spark at the spark plug wire(s).
You might already have a misfire code and know which cylinder to test for spark first or maybe you don't know, either way I recommend that you test all of the spark plug wires for spark.
Remember also that the successful outcome of your trouble-shooting/diagnostic lies in the usage of an HEI spark tester (don't have an HEI spark tester? Need to buy one? You can buy it here: OTC 6589 Electronic Ignition Spark Tester).
Let's get started:
- 1
Remove the spark plug wire (high tension cable) from the spark plug.
- 2
Connect the spark tester to the spark plug wire (see photo above).
- 3
Connect the spark tester to the battery negative (-) post with a battery jump start cable as shown in the photo above.
- 4
Have your helper crank the vehicle while observing the spark tester from a safe distance.
CAUTION: The vehicle may or may not start, either way be careful! - 5
You're gonna' get one of two results: Spark or no spark.
- 6
Now repeat this test on the other cylinders.
IMPORTANT: Read the following options carefully to interpret your NO SPARK result or results.
The key to diagnosing a bad coil pack is remembering that two cylinders get spark at the exact same time (from the same coil inside the coil pack).
So if you get a NO SPARK result from two spark plug wires, it's important that you verify if those two spark plug wires connect/feed spark to cylinders 1 and 5 or if they connect to cylinders 2 and 6 or if they connect to cylinders 3 and 4.
CASE 1: You got spark from all six spark plug wires. This indicates that the ignition coils and spark plug wires are OK. The cause of your misfire condition is not due to a bad ignition coil. Go to: TEST 9: Other Things That Can Cause A Misfire to see further tips and suggestions.
CASE 2: You got NO spark from only one spark plug wire. The next step is to check for spark directly on the coil pack tower that feeds that spark plug wire with spark. Go to: TEST 2: Testing For Spark Directly On The Coil Tower.
By checking for spark directly on the coil tower (of the spark plug wire that didn't spark) you'll be able to verify if the wire itself is good or bad.
CASE 3: You got NO spark from two spark plug wires that connect to spark plugs of paired cylinders 1 and 5, cylinders 2 and 6, or cylinders 3 and 4. This usually indicates that the coil pack is bad.
More specifically, that one of the ignition coils (that make up the coil pack) is fried. In TEST 3 you'll do some further tests to make sure.
Go to: TEST 3: Testing For Spark Directly On The Coil Tower (Paired Cylinders).
CASE 4: You got NO spark from two spark plug wires that DO NOT connect to paired cylinders. The next step is to test each coil pack tower directly for spark one at a time. Go to: TEST 8: Testing For Spark Directly On The Coil Tower.
CASE 5: You got NO spark from ALL of the spark plug wires. This usually indicates that power is missing from the power circuit or that the crankshaft position sensor is bad. Go to: TEST 4: Testing The Power (12 Volts) Circuit.
TEST 2: Testing For Spark Directly On The Coil Tower
You've been directed to this test step because you got a no spark result from only one spark plug wire in TEST 1.
The purpose of this test is to see if the spark plug wire is good or bad.
You'll do this by verifying that the ignition coil tower (that feed spark to the spark plug wire) is sparking. You can easily accomplish this by testing for spark directly on the coil pack tower.
This is what you'll need to do:
- 1
Remove the spark plug wire that did not fire off spark from the ignition coil pack.
- 2
Place the spark tester directly on the ignition coil tower, in place of the spark plug wire you just removed (see photo above).
- 3
Connect the spark tester to the battery negative (-) post with a battery jump start cable.
- 4
Have your helper crank the engine.
CAUTION: The vehicle may or may not start, either way be careful! - 5
You're gonna' get one of two results: Spark or no spark.
Let's take a look at what your test result means:
CASE 1: You got spark. This is the correct test result and confirms that the ignition coil is good. It also condemns the spark plug wire as bad.
Replace all of the spark plug wires as a set. Replacing the spark plug wires (as a set) will solve the misfire condition and the misfire code lighting up the check engine light (CEL) on the instrument cluster.
CASE 2: You got NO spark. Then this result indicates that the ignition coil is bad. Replacing the ignition coil will solve the misfire condition and the misfire code lighting up the check engine light (CEL) on the instrument cluster.
