TEST 7: Switching Signal Test For Cylinders 3/6
In this test step, you'll be verifying that the PCM is creating and feeding the Switching Signal (for cylinders 3 and 6) with an LED light.
The 3/6 Switching signal is the activation signal that gets the ignition coil pack to fire off spark to cylinders 3 and 6.
This is a very simple and straight forward process in which the ignition coil pack must be connected to its connector.
NOTE: To see an example of the LED light, go here: The LED Light Test Tool And How To Make One.
NOTE: This test is done with the ignition coil pack connected to its electrical connector.
These are the test steps:
With an appropriate tool, connect the black lead of the LED light to the wire identified with the number 1 in the image above.
This is the circuit that feeds the Switching signal to the ignition coil (within the coil pack) that feeds spark to cylinders 3 and 6 simultaneously.
Connect the red lead of the LED light to the battery positive (+) terminal.
Have your helper crank the engine.
NOTE: The engine may start so be careful.
If the engine starts, have your helper turn it off.
The LED light should flash ON and OFF the whole time the engine is cranking and during the time it was running.
Let's see what your test results mean:
CASE 1: The LED light flashed ON and OFF the whole time the engine was cranking or running. This is the correct test result and it confirms that the PCM is providing the Switching signal and the circuit is OK.
This result confirms that the ignition coil pack is bad and needs replacement if you have:
- Confirmed that the spark plug wires for cylinders 3 and 6 are not sparking (TEST 1).
- Confirmed that the ignition coil towers for cylinders 3 and 6 are not sparking (TEST 3).
- In this test section, you've confirmed that the ignition coil pack is receiving the activation signal for cylinders 3 and 6.
CASE 2: The LED light DID NOT flash ON and OFF the whole time the engine was cranking or running. This test result tells you that the Switching signal is not present.
The most likely cause of this missing signal is either an open-circuit problem in the circuit between the connector and the PCM or the PCM is fried (altho' a fried PCM is rare).
This result eliminates the coil pack itself as the source of the misfire condition or no-spark condition.
TEST 8: Other Possible Misfire Causes
So you've done all of the spark tests, and your Chrysler (or Dodge or Eagle or Plymouth) mini-van is still misfiring. Well, here are a couple of suggestions that might help:
- Inspect the inside of the spark plug wire boots and remove the spark plugs to visually check their ceramic insulators for carbon tracks
- The orange arrows in the photo above point to what carbon tracks look like.
- Replace the components as affected with carbon tracks.
- Engine compression test
- This is one of the easiest, yet most overlooked test to find the cause of a misfire condition.
- You'll need an engine compression tester of course.
- The engine between cylinders should not vary more 15%.
- Fuel injector test
- The fastest way to test them is checking the resistance (Ohms) value of each one and then comparing them to each other.
- Any resistance that's not within the average of the others indicates the fuel injector is fried. If the Ohms values are nearly identical, then the fuel injectors are OK and not the cause of the misfire.
- You can buy a specific fuel injector tester (on line) that activates them by a predetermined pulse width. This tester is used in conjunction with a fuel pressure gauge (which will measure the fuel pressure drop of the activated injector).
If this info really saved the day, buy me a beer!