Common Causes Of A Misfire Diagnostic Trouble Code (DTC)
Before we jump into the testing of the COP coils, I want to make you aware that there are several other things that can cause a misfire condition on your 4.7L Dodge pickup or SUV.
Here are the most common causes:
- Bad COP ignition coil.
- A bad COP coil will cause a specific misfire code like P0301, P0302, P0303, P0304, P0305, P0306, P0307, P0308.
- The focus of this article is to test for a bad COP ignition coil.
- Leaking intake manifold gaskets.
- An intake manifold gasket that's no longer sealing the vacuum inside the intake manifold will usually cause a Random Misfire Code P0300.
- Spark plug issues.
- Incorrectly gapped spark plugs.
- Broken spark plug. Specifically, a cracked porcelain insulator.
- Water in the spark plug Wells caused by washing the engine.
- Engine mechanical issues.
- Low engine compression in one or two cylinders will cause a misfire.
- Blown head gasket.
It seems like a daunting list of ‘possibles’ but don't let the above list worry you. The most important first step, in your misfire trouble code diagnostic, is to eliminate the COP ignition coils first (and this is the main focus of this tutorial).
TEST 1: Checking For Misfire Codes
The very first thing you need to do, is to connect your scan tool to your vehicle and check for misfire codes.
Why? Because the misfire code will help you in identifying which cylinder is the one that could have a bad ignition coil and knowing which ignition coil to test is half the diagnostic battle.
Now, if you don't have a scan tool, you can still use the info in this tutorial but you'll need to do a cylinder balance test first. For more info on this, go to: TEST 4: Cylinder Balance Test.
To get started, choose from one of the cases below:
CASE 1: You have a misfire code. The next step is to identify the cylinder that's misfiring so that you can test the right ignition coil (remember, the 4.7L engine has a total of 8 COP ignition coils).
For help in identifying the misfire code engine cylinder, go to: How To Identify The Misfire Code Engine Cylinder.
Once you have identified the engine cylinder which the misfire code is accusing of misfiring, go to: TEST 2: Check The Ignition Coil For Spark.
CASE 2: You have a P0300 Misfire Code. This means that whatever is causing the misfire condition, is affecting all of the engine cylinders and not just one.
This code, the (P0300) usually rules out a bad COP ignition coil as the culprit. For more info on troubleshooting a P0300, go to: TEST 5: Common Causes Of A P0300.
CASE 3: You DO NOT have any misfire codes - This means that the rough idle that you're experiencing in your vehicle is going to be a little tough to diagnose. Here are a couple of suggestions:
- Start with a cylinder balance test to see if you can identify the weak cylinder.
- Remove and visually inspect:
- Spark plugs.
- COP coils
- An engine compression test may be a good idea too.
TEST 2: Check The Ignition Coil For Spark
The very first thing you need to do, is check to see if the COP ignition coil is sparking or not.
My instructions below call for an HEI spark tester and if you don't have one, you may be wondering if you can use any other type of spark tester.
And the answer is yes you can use any type of spark tester you want or have. The main reason I use and recommend the HEI spark tester is because this bad boy is accurate (and you don't have to worry about interpreting the color of the spark).
OK, to get your COP ignition coil diagnostic going, this is what you need to do:
Remove the ignition coil from its place on the valve cover.
Connect an HEI spark tester to the ignition coil.
Ground the HEI spark tester with a battery jump start cable directly on the battery negative terminal.
When everything is set up, have a helper crank the engine while you observe the spark tester.
The spark tester will do one of two things: spark or not spark.
Let's take a look at your test results:
CASE 1: You got spark. This tells you that ignition coil is OK.
So, if you have a misfire code for the specific engine cylinder this COP coil belongs to then you need to look at the following things:
- Oil dripping onto the spark plug and COP coil boot from the valve cover gasket.
- Spark plugs for carbon tracks.
- Low engine compression in this cylinder.
CASE 2: You DID NOT get spark. Around 90% of the time, this test result tells you that the COP ignition coil is bad. To make sure, there's one more thing that you need to do.
And this is to make sure that the COP ignition coil (that did not spark) is getting both power and the switching signal. This can very easily be accomplished by simply swapping a good and sparking COP coil in place of the one that's not sparking and repeating this test. For this test, go to: TEST 3: Swap The ‘No Spark’ COP Coil.