TEST 2: Testing For Spark Directly On The Distributor Cap
If you found, in TEST 1, that one or more spark plug wires did not spark, then the next step is to check for spark on the distributor cap towers those spark plug wires connect to.
If the distributor tower sparks, then you can conclude that its spark plug wire is bad (since it did not spark in TEST 1).
Alright, these are the test steps:
Disconnect the spark plug wire that did not spark from its tower (on the distributor cap).
Place the spark tester in the tower as shown in the photo above.
Ground the spark tester to the battery negative (-) terminal using a battery jump start cable.
Have your helper crank the engine while you observer the spark tester from a safe distance.
The spark tester should spark.
Let's interpret your test results:
CASE 1: The spark tester sparked. This is the correct and expected test result.
You can also conclude that the spark plug wire is bad (that connects to that tower) if you have:
- Confirmed that the spark plug wire that connects to that tower DID NOT spark in TEST 1.
Replace all of the spark plug wires with a new set.
Here's why: As the spark plug wire ages, its normal resistance to spark increases to the point that the wire can not and does not transmit the spark to the spark plug. This will either cause a misfire, or a lack of power, or a no-start condition. spark plug wires don't last forever, especially after-market ones (average life-span is 3 to 4 years).
CASE 2: The spark tester DID NOT spark. You can conclude that the distributor cap is bad if you have:
- Confirmed that some but not all of the spark plug wires sparked in TEST 1.
- Confirmed that the distributor cap tower you just tested for spark DID NOT spark.
Replace the distributor cap and rotor with a new set.
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 stops the spark from passing thru' to the spark plug wires.
TEST 3: Testing For Spark Directly On The Ignition Coil
In this test section, we're gonna' remove the distributor cap and test the ignition coil's tower for spark.
If the ignition coil's tower sparks, then we can conclude that that the distributor cap and rotor are bad are behind the no-spark test result from all of the spark plug wires.
If the ignition coil does not spark, then the next step is to make sure that the ignition coil is getting power (TEST 4).
IMPORTANT: This test requires that the ignition coil be tested with the distributor cap off of the distributor. It's important that this test be done with a spark tester attached to the ignition coil. The car cannot/should not be cranked without the ignition coil being grounded by a spark tester.
Let's get testing:
Remove the distributor cap.
Connect the spark tester directly on the ignition coil's tower with a piece of vacuum hose (as shown in the photo above).
The arrow in the photo points to the vacuum hose holding the spark tester to the ignition coil's tower.
Have your helper to crank the engine while you observer (1) the spark tester and (2) that the distributor rotor is turning.
You're gonna' get one of the 3 results:
1.) Spark and the distributor rotor turns.
2.) No spark and the distributor rotor DOES NOT turn.
3.) No spark and the distributor rotor DOES turn.
Let's interpret your test results:
CASE 1: You got spark and the distributor rotor turns. This the correct test result. It lets you know that the ignition coil is good and that the timing belt is not busted.
With this test result you can conclude that the distributor cap and distributor rotor are bad if you have:
- Confirmed that none of the spark plug wires are sparking (TEST 1).
- Confirmed that the ignition coil is sparking.
CASE 2: You got NO spark and the distributor rotor DOES NOT turn. This is the result of a timing belt that has broken.
Here's why: The crankshaft rotates the distributor rotor via the timing belt. How? Well, the distributor is physically connected to the camshaft. The camshaft is rotated by the crankshaft via the timing belt. A broken timing belt won't rotate the camshaft and by extension, the distributor rotor. And if the distributor shaft does not rotate, the computer will not receive the position sensor signals and the ignition system will not work to produce spark.
CASE 3: You got NO spark and the distributor rotor DOES turn. Then further testing is required to see if the problem is due to a bad ignition control module or a bad ignition coil.
Your next step is to make sure that the ignition coil is getting power (12 Volts). Go to: TEST 4: Making Sure The Ignition Coil Is Getting Power.