How To Test The Ignition Coils (2002-2005 4.2L Chevrolet TrailBlazer, GMC Envoy)

TEST 4: Other Common Misfire Causes

Quite a few things can cause a misfire problem that'll light up a check engine light, on your Chevrolet TrailBlazer or GMC Envoy, with a misfire trouble code.

So if your ignition coil tests confirm the ignition coil belonging to the dead (misfiring) cylinder is sparking and thus not defective, I recommend taking a look at the following:

1. Check for carbon tracks on the inside of the ignition coil's boot (see photo above).
   • You'll have to remove all of the spark plugs and visually inspect their ceramic insulators and the inside of each spark plug wire boot to see if carbon tracks have developed. The photo above shows you what a carbon track looks like inside the boot and on the spark plug.
2. Check to see if the ignition coil and spark plug are swimming in engine oil inside the spark plug tube.
3. Check the to see if the dead cylinder's spark plug is broken.
4. The dead cylinder has a compression problem.
   • You can find the engine compression test here: How To Test Engine Compression (2002-2009 4.2L Chevrolet TrailBlazer).
5. Intake manifold gasket leaking air into the engine.
6. The dead cylinder's fuel injector is bad.

More GM 4.2L Test Tutorials

If this tutorial was helpful, be sure and take a look at all of the Chevrolet TrailBlazer and GMC Envoy test tutorials in this index: GM 4.2L Index Of Articles.

Here's a sample of the tutorials you'll find there:

• How To Test For A Blown Head Gasket (2002-2009 4.2L Chevrolet TrailBlazer).
• How Often Should I Replace The Spark Plugs? (2002-2009 4.2L Chevrolet TrailBlazer).
• How To Test Engine Compression (2002-2009 4.2L Chevrolet TrailBlazer).
• Electronic Throttle Body Tests (2002-2007 4.2L Chevrolet TrailBlazer).