TEST 6: Secondary Ignition Coil Tower Spark Tests (Paired Cylinders)
IMPORTANT: This test only applies if in TEST 3 you had 2 intake manifold side spark plug wires that did not spark and they connect to paired cylinders. Paired cylinders are cylinders that get spark simultaneously. They are cylinders #1 and #4 or cylinders #2 and #3.
In this test section, we're gonna' check for spark directly on the secondary ignition coil pack towers of the spark plug wires that did not fire off spark in TEST 1.
If both towers do not spark, then you can confidently conclude that the secondary ignition coil is defective.
If both towers spark, you can conclude that the spark plug wires are defective.
NOTE: The spark tester must be held in place in the ignition coil pack tower. You can easily and safely do this by Grounding the spark tester with a battery jump start cable. The battery jump start cable will make it easy (and safe) to hold the spark tester in the coil tower.
Let's get testing:
Disconnect the spark plug wire that did not spark in TEST 3 from its ignition coil tower.
Place the spark tester in the ignition coil tower. This is the coil tower that you just removed its high tension wire.
Ground the spark tester directly to the battery negative (-) terminal using a battery jump start cable.
Have your helper crank and start the engine while you observe the spark tester.
The spark tester should spark with the engine running.
Repeat the spark test on the other ignition coil tower whose spark plug cable did not spark in TEST 1.
Let's analyze your spark test result:
CASE 1: The spark tester sparked on both towers. This is the correct test result and lets you know that the secondary ignition coil pack is good.
This test result also tells you that the spark plug wires (high tension wires) that connect to these 2 coil towers are defective. Replace all of the 8 spark plug wires with a new set.
Spark plug wires will eventually stop transmitting spark from the ignition coil to the spark plug. This is a very common problem.
CASE 2: The spark tester DID NOT spark on both towers. This test result usually means that the secondary ignition coil pack is defective and needs to be replaced.
To be sure (it's defective), you need to make sure that the ignition coil is getting its activation signal. If cylinders 1 and 2 coil towers are not sparking, go to: TEST 7: Verifying The Activation Signal For Cylinders 1 And 4.
If cylinders 2 and 3 coil towers are not sparking, go to: TEST 8: Verifying The Activation Signal For Cylinders 2 And 3.
CASE 3: The spark tester sparked on only one tower. This test result lets you know that the secondary ignition coil pack is defective and needs to be replaced (because both should be sparking).
TEST 7: Verifying The Activation Signal For Cylinders 1 And 4
In this test step, you're going to verify that the individual ignition coil (within the coil pack) that fires spark to cylinders 1 and 4 is getting its activation signal from the fuel injection computer.
If you're testing the primary coil pack, you'll be testing the tan with white stripe (TAN/WHT) wire of the primary ignition coil pack's electrical connector.
If you're testing the secondary coil pack, you'll be testing the tan with light green stripe (TAN/LT GRN) wire of the secondary ignition coil pack's electrical connector.
NOTE: To check for the ignition coil's activation signal, you'll need to use an automotive LED light. You can see an example of this tool here (and how to make one): The LED Light Test Tool And How To Make One.
WIRING DIAGRAM: You can find the ignition system wiring diagram here: Ignition System Circuit Diagram (1998-2001 2.5L Ford Ranger).
Alright, let's get testing:
With an appropriate tool, connect the black lead of the LED light to the 1/4 activation signal wire.
If you're testing the primary ignition coil pack, this wire is the TAN/WHT wire.
If you're testing the secondary ignition coil pack, this is the TAN/LT GRN wire.
Connect the red lead of the LED light to the battery positive (+) terminal.
Have your helper crank and start the engine.
The LED light will flash ON and OFF, the whole time the engine is cranking and running if the activation signal is present.
Let's find out what your test result means:
CASE 1: The LED light flashed ON and OFF. With this test result you can conclude that the fuel injection computer is providing the activation signal that the ignition coil needs to start firing spark to cylinders 1 and 4 and the circuit is OK.
This test result confirms that the ignition coil pack is defective (and needs to be replaced) only if you have confirmed that coil towers for cylinders 1 and 4 are not firing spark.
CASE 2: The LED light DID NOT flash ON and OFF. This test result tells you that the ignition coil that fires spark to cylinders #1 and #4 is not getting its activation signal.
This usually means that the signal wire has an open-circuit problem between the connector or the computer or the computer is fried (altho' this is a very rare condition).
With this result you have eliminated the coil pack as the source of the misfire condition.