TEST 7: Testing The Trigger Signal Without A Multimeter
You've heard the saying that ‘there's more than one way to skin a cat’ (I love cats, please no hate mail over this), well in this test step I'll show you how to verify that the Triggering Signal is indeed present on the Coil-On-Plug ignition coil that didn't fire off spark without having to use a multimeter.
Disconnect and remove the Coil-On-Plug (COP) ignition coil that didn't fire off spark in TEST 1 and 2.
Remove one of the adjacent COP ignition coils (that you know for a fact that it's firing off spark) next to the one you just removed.
Connect the COP ignition coil (that sparks) to your HEI spark tester
Now connect (this same coil that sparks) to the connector of the ignition coil that did not spark.
Now, have your trusty assistant crank the engine and notice if the HEI spark tester spark. Be careful, the engine will probably start.
If the Triggering Signal is present, then this COP ignition coil will fire spark connected to this connector. If the Triggering Signal is missing for any reason, it won't spark.
Let's take a look at what your test results mean:
CASE 1: If you got spark. Then this test result tells you that the Triggering Signal is present.
This result also tells you that the Coil-On-Plug ignition coil on your GM vehicle is bad and needs to be replaced only if:
- The coil is not firing spark in TEST 1 and 2.
- It's getting power (12 Volts DC) in TEST 3.
- It's getting chassis Ground in TEST 4.
- It's getting PCM ground in TEST 5.
- It's getting the triggering signal from the PCM (TEST 7).
CASE 2: If you got NO spark. Re-check all of your connections and repeat the test again. If still no spark, then this results eliminates the ignition coil as the source of the NO SPARK condition/misfire, since without the Triggering Signal the COP ignition coil will not work.
TEST 8: Carbon Tracks And Other Stuff
You've reached this test step because there's a good possibility that the misfire, that your GM vehicle is experiencing, isn't due to a bad Coil-On-Plug ignition coil. This section will delve into other possible causes.
One of them is carbon tracks. Carbon tracks are one of the leading causes of misfires. This condition usually occurs on vehicles that have over 100,000 miles on them and is a result of lack of maintenance (since the spark plugs and spark plug wires should have been replaced at this mileage or before). Of course the spark plugs and spark plug wires should perform flawlessly for one hundred thousand miles (100,000) theoretically speaking (I never learned to speak Theoretical). But this doesn't really happen in real life.
So, to make the long story short (you're probably already getting eye-strain from reading this article), you should check for carbon tracks on the spark plug wires and the spark plugs. In the photos in the image viewer, you'll see what they look like. Below are other suggestions to look into:
- Low engine cylinder compression in one or more cylinders.
- Bad fuel injectors.
- Leaking intake manifold gasket.
- Fuel pressure regulator gone bad and leaking fuel into its vacuum hose. I SEE THIS ALOT!!!!.
If this info really saved the day, buy me a beer!