TEST 1: Identify The Misfiring Cylinder
The very first thing you need to do is identify the misfiring cylinder (if you haven't already). This can be very easily done with a simple cylinder balance test.
For those of you who may not know what a cylinder balance test, this test involves unplugging each ignition coil (from its 3-wire electrical connector) while the engine is running. Why? To see if unplugging that ignition coil's 3-wire electrical connector has an effect on the engine's idle. If unplugging the electrical connector does not worsen the engine's idle, then that cylinder is ‘dead’.
I'm going to emphasize the above point one more time: If the cylinder is ‘dead’, then when you unplug the ignition coil, the engine's idle will not get rougher. If the cylinder is working like it should, then unplugging the ignition coil from its connector will cause the engine's idle to get worse (rougher) and you'll see/notice a drop in the engine's RPMs too.
NOTE: When performing the cylinder balance test, it's important that you don't keep the ignition coil unplugged for too long a time, since this will add unburned gasoline to an already overburdened catalytic converter (remember, you already have a misfire that's adding unburned fuel to the exhaust system).
Once you have identified the misfiring cylinder, the next step is to see if the ignition coil is sparking. This is what you'll need to do:
- Disconnect the COP ignition coil from its electrical connector and remove it from the engine.
- Attach a dedicated spark tester to the COP coil (see photo above).
- Here, I recommend using an HEI spark tester because of its accuracy in diagnosing a no spark condition (to find out more about the HEI spark tester here: HEI Spark Tester).
- The spark tester can be grounded directly to Battery Ground using a Jump Start Cable (as shown in the photo below).
- Reconnect the COP ignition coil to its electrical connector.
- Have a helper crank the engine while you observe the spark tester from a safe distance.
- You're gonna' see one of two results: either the spark tester sparks or it doesn't.
- OK, once you're done, take a look at the following test results:
CASE 1: The spark tester sparked: This tells you that the ignition control module is activating the ignition coil.
This test result not only tells you that the ignition control module IS NOT the cause of the misfire, but that the ignition coil is OK too.
You'll need to check engine compression, fuel injectors, spark plugs, etc. to find the cause of the ‘dead’ cylinder.
CASE 2: The spark tester DID NOT spark: The next step is to perform TEST 2 to see if the cause is the ignition control module. Go to: TEST 2.
TEST 2: Swapping The Ignition Coils
In TEST 1, you did two different tests. One was a cylinder balance test (which helped you identify the ‘dead’ cylinder) and the other was a spark test.
In this test step, I'm gonna' ask you to swap the ignition coil you just confirmed as not sparking (in TEST 1) with one of the other 3 ignition coils (these other 3 coils are good because when you unplugged them from their connector, the engine's idle got lower and rougher, thus confirming that they're working beautifully).
Alright, this is what you'll need to do:
- Unplug and remove the ignition coil from its electrical connector (the one that you just confirmed as not sparking in TEST 1).
- Unplug and remove one of the other 3 ‘good’ ignition coils that did cause the engine's idle to get worse when you did the cylinder balance test.
- Now, swap these two and bolt down (on the Valve Cover) the one that belonged to the ‘dead’ cylinder, and connect it to the its 3 wire electrical connector.
- Connect the spark tester to the ‘good’ ignition coil.
- You're not gonna' bolt this ignition coil down on the Valve Cover.
- Now, connect the ‘good’ ignition coil to it's electrical connector.
- When ready, have your helper start the engine briefly.
- You're gonna' get one of two results:
- Either the ignition coil will spark.
- The ignition coil won't spark.
OK, let's interpret your test results:
CASE 1: The ignition coil sparked. This test result tells you that the ignition coil that you removed from the ‘dead’ cylinder is bad and needs to be replaced.
Since the other ignition coil is sparking (in the place where the other wasn't), this test result also tells you that the ignition control module is OK and activating the ignition coil.
I'm going to go into more detail about this, so that you can trust your test result:
- In TEST 1, you confirmed that you did indeed have a ‘dead’ cylinder (with the cylinder balance test).
- You also confirmed that the ignition coil that belonged to the ‘dead’ cylinder was not sparking using a dedicated spark tester.
- In this test (TEST 2), you swapped out the ignition coil that was bolted to the ‘dead’ cylinder with one of the other 3 ‘good’ that are sparking
- You know that they are sparking because unplugging them in TEST 1 made the engine's idle get rougher/lower.
- The ignition coil sparked, thus confirming that the other ignition coil is bad and needs to be replaced.
This also confirms that the ignition control module is sending the Switching Signal (that activates the ignition coil) and thus the ignition control module is OK.
CASE 2: The ignition coil DID NOT spark. This usually means that the ignition control module is bad but to make absolutely certain, you need to spark test (with a dedicated spark tester) the ignition coil that wasn't sparking (in TEST 1). For more specifics on this, go to: TEST 3.