TEST 3: Swap The ‘No Spark’ COP Coil
So far, you've confirmed that there's a COP coil that's not sparking (TEST 2) and as mentioned in TEST 2, this usually means that you have a bad COP coil on your hands but not always.
To make sure that the COP coil is truly fried, in this test step, you're gonna' swap ignition coils and test for spark again.
If the good COP ignition coil sparks (in the place of the one that did not spark) then you now know beyond a shadow of a doubt that the COP coil is getting all 3 signals from its connector.
This is what you'll need to do:
Unplug and remove the COP ignition coil that did not spark.
Choose one of the other COP coils that is sparking and remove it from its place.
Verify that the COP coil is sparking by testing it with your spark tester (if necessary).
Connect the good COP coil to the connector of the bad COP ignition coil.
Next, connect the HEI spark tester to this good COP coil.
Ground the HEI spark tester with a jump start cable directly on the battery negative terminal.
Place the bad COP ignition coil in the location of the good one you just removed and bolt it down.
Once everything is ready, have your helper crank the engine.
The good ignition coil should spark.
Let's take a look at your test results:
CASE 1: The COP ignition coil sparked. This tells you that the COP coil that did not spark in TEST 2 is bad and needs to be replaced.
If you need/want to save a few bucks and buy a good quality COP coil for your vehicle, look at this section: Where To Buy A COP Ignition Coil for my suggestion.
CASE 2: The COP ignition coil DID NOT spark. This tells you that the COP coil (you just swapped) is good and that the reason it's not sparking is a lack of power or a switching signal.
The next step for you is to:
- Check that one of the two wires is providing power (10 to 12 Volts).
- This is usually the light green with orange stripe wire.
- Check that the other wire is providing the PCM's switching signal.
What usually happens here is one of two things: either the switching signal wire has an ‘open-circuit’ problem between the coil connector and the PCM connector or the PCM goes bad.
Having a bad PCM is a rare thing to happen, but it does happen. Although it's beyond the scope of this article to test this condition, you now at least know what direction your diagnostic needs to take.
TEST 4: Cylinder Balance Test
A cylinder balance test will help you determine which engine cylinder is the one missing (misfiring), especially when the PCM does not set a specific misfire trouble code.
In a nutshell, the cylinder balance test involves starting the engine, letting it idle, and then unplugging one fuel injector at a time to see which cylinder is ‘dead’.
By ‘dead’ I mean not contributing to engine power. Now, let me go into more specifics: If an engine cylinder is getting both spark, fuel, and has good compression and you unplug its fuel injector connector, you're gonna' visibly see the engine shake more.
But if that engine cylinder is not getting one of the three (fuel, spark, or compression), unplugging the fuel injector WILL NOT cause a difference in idle at all (the engine will not shake more).
This type of cylinder balance test is very effective at finding the ‘dead’ cylinder. What I usually do, to further aid in finding the dead cylinder, is attaching a vacuum gauge to the intake manifold and as I unplug each fuel injector I listen/look for the change in idle and see if the vacuum gauge's needle also records the change.
OK, this is what you need to do:
- Start the engine and let it idle.
- Once the idle has stabilized, briefly unplug the fuel injector for cylinder #1.
- If the cylinder is ‘dead’
- You won't see/feel a difference in the engine's idle quality.
- If the cylinder is NOT ‘dead’
- You will see/feel a difference in the engine's idle quality.
- Now reconnect the fuel injector and move on to the next fuel injector and disconnect and connect its connector and check for a drop in engine RPM's.
- Test all engine cylinders in this manner.
Let's take a look at your test results:
CASE 1: The cylinder balance test identified a ‘dead’ cylinder. Now that you have identified the cylinder with the misfire, the next step is to check and confirm that it's not being caused by a bad COP (Coil-On-Plug) ignition coil.
This involves checking the COP ignition coil for spark, you can now start with: TEST 2: Check The Ignition Coil For Spark.
CASE 2: The cylinder balance test DID NOT identify a ‘dead’ cylinder. This tells you that you don't have a specific ‘dead’ cylinder.
Now, if your vehicle is experiencing a rough idle condition then it's something that's affecting all of the cylinders and not just one. My suggestion in this case is to look at: TEST 5: Common Causes Of A P0300.