TEST 2: Making Sure The Ignition Coil Is Getting 12 Volts
The ignition coils need 10 to 12 Volts to fire spark. The wire that delivers this voltage is the red with light green stripe (RED/LT GRN) wire of the ignition coil's 2-wire connector.
It typically connects to the terminal labeled with the number 2 in the illustration of the ignition coil pigtail connector above.
In this section, we're gonna use a multimeter to check if 10 to 12 Volts are present in the RED/LT GRN wire.
NOTE: Your multimeter's test lead tip might not fit the metal terminal inside the connector because the slot is very small. If the test lead tip can't safely probe the terminal, use an adapter on the test lead. Otherwise, you could damage the terminal or the connector, which would require you to replace the connector.
These are the test steps:
- 1
Disconnect the ignition coil that did not spark from its 2-wire connector.
- 2
Place your multimeter in Volts DC mode.
- 3
Connect the black multimeter test lead to the battery negative (-) terminal.
- 4
Gently probe the female terminal of the connector that connects to the wire labeled with the number 2 (see photo above) with the red multimeter test lead.
- 5
Have your helper turn the key to the ON position.
- 6
You should see 10-12 Volts on your multimeter.
Let's take a look at what your test results mean:
CASE 1: The multimeter registered 10-12 Volts (or the test light lit up). This test result tells you that the power circuit is OK and is delivering voltage.
The next step is to test the Switching signal circuit, go to: TEST 3: Checking The Ignition Coil's Activation Signal.
CASE 2: The multimeter DID NOT register 10-12 Volts (or the test light DID NOT light up). This test result confirms that the power circuit has a problem.
This result eliminates the COP ignition coil as the source of the misfire condition. The power circuit is shared by all of the COP ignition coils.
TEST 3: Checking The Ignition Coil's Activation Signal
As mentioned at the beginning of this tutorial, the ignition coils receives an activation signal to fire spark from the PCM.
The wire that delivers this activation signal is the one that connects to the terminal labeled with the number 1 of the ignition coil's 2-wire connector.
It's important to note that the color of this wire will vary depending on the location of the ignition coil you're testing. Don't worry about this, since you only have two wires coming out of the connector. The activation signal wire will always be the non-red with light green stripe wire.
To check for the presence of the ignition coil's activation signal (while we crank the engine), we'll use a 12 Volt test light.
NOTE: There's a good chance your 12V test light probe's tip won't be able to probe the metal terminal inside the connector because the terminal's slot is very small. If the test lead tip can't safely probe the terminal, use an adapter. Otherwise, you could damage the terminal or the connector, and you'll need to replace the connector.
Let's get started:
- 1
Disconnect the ignition coil from its connector.
- 2
Connect the crocodile clip of the 12V test light to the battery positive (+) terminal.
- 3
Gently probe the terminal of the connector labeled with the number 1.
- 4
Have your helper crank up the engine as you observe the 12V test light.
- 5
The 12V test light should flash ON and OFF the whole time the engine is cranking and running.
Let's take a look at what your test results mean:
CASE 1: The test light flashed ON and OFF. This test result confirms that the ignition coil's activation signal is present.
This result also indicates that the Coil-On-Plug ignition coil on your Ford Crown Vic or Mercury Grand Marquis is bad and needs to be replaced if you have:
- Confirmed that the ignition coil is not sparking (TEST 1).
- Confirmed that the ignition coil is getting 12 Volts (TEST 2).
- Confirmed that the ignition coil is getting an activation signal (this test section).
CASE 2: The test light DID NOT flash ON and OFF. Re-check all of your connections and repeat the test again.
If still no flashing ON and OFF, then this results eliminates the ignition coil as the source of the no-spark condition/misfire, since without the Switching signal the ignition coil will not work.
There are several possible causes for this that I've seen time and time again with the most common being: An open-circuit problem in the wire that feeds the Switching signal between the fuel injection computer and the COP ignition coil. The second most common: A fried fuel injection computer. Although testing these two conditions are beyond the scope of this article, you have at least eliminated the ignition coil itself as the cause of the problem.
Other Common Causes Of A Misfire
Quite a few other things, besides a bad ignition coil, can cause a cylinder misfire problem and its respective misfire diagnostic trouble code (DTC) to set. Here are a few things you might need to check if your test results indicate all of the ignition coils are good:
- Carbon Tracks: The spark plug boots spark plugs have developed carbon tracks (see image above). These carbon tracks create a conductive path that diverts electricity (the spark) away from the spark plug tip, causing a cylinder misfire. These carbon are usually the result of engine oil leaking into the spark plug tube.
- Broken Fuel Injector Connector: The fuel injector connector's locking tab is broken. This is a very, very common problem with all Ford vehicles. So, if you have a broken fuel injector connector locking tab, you've probably have found the cause of the misfire!
- Damaged Female Terminals (In Connector) The ignition coil connector's female terminals aren't making solid contact with the ignition coil's male spade terminals. This issue, often due to human error, likely stems from inserting objects that are too thick into the connector's female terminals, causing them to permanently open up. As a result, this leads to an intermittent false-contact issue.
- Open-Circuit Problem In The Wiring: An open in the wiring has developed somewhere in the wiring harness that doesn't let the Switching signal thru'. This is also normally caused by human error after an engine replacement.
- Ant-Freeze/Engine Oil Leak: Anti-freeze or engine oil leaking into the spark plug tube and drowning the spark plug and spark plug boot.
- Broken Ignition Coil Connector: The ignition coil's connector's locking tab has broken. This locking tab is the one that makes sure the connector doesn't become unplugged from the ignition coil. This tab usually breaks when the ignition coil is disconnected, either to replace it or the spark plugs.
- Low Compression Problem: The engine may have one or more cylinders with low engine compression. I suggest testing engine compression:
- Bad Or Clogged Fuel Injector: There's a good chance that the cylinder misfire issues is caused by a bad or clogged fuel injector. The following tutorials may be helpful:
More 4.6L Crown Vic And Grand Marquis Tutorials
There are quite a few 4.6L Ford Crown Victoria (Mercury Grand Marquis) 'how to' tutorials and wiring diagrams in this index:
E-Series Vans: You can find all of the available tutorials and wiring diagrams for the 4.6L and 5.4L V8 E-Series vans in this index:
F-Series Pickups: You can find all of the available tutorials and wiring diagrams for the 4.6L And 5.4L V8 F-Series pickups in this index:
- 4.6L, 5.4L Ford F150, F250, And F350 Index of Articles (at: easyautodiagnostics.com.com).
If this info saved the day, buy me a beer!
