How Often Should I Replace The Spark Plugs? (2002-2009 4.2L Chevrolet TrailBlazer)

Which Spark Plugs Should I Buy: AC Delco Or Brand X?

The spark plug that your 4.2L Chevrolet TrailBlazer or GMC Envoy comes with from the factory is the AC Delco brand spark plug.

This is the spark plug that you should buy and install on your TrailBlazer or Envoy when it's time to replace them.

Now having said that, any spark plug from any other brand that is specifically designed to work on your particular Trailblazer or Envoy will work.

Of course, some spark plugs are cheaper than others. Here are my recommendations:

If your engine is burning oil: I would suggest buying the cheapest platinum tipped spark plugs (even if it's Brand X spark plugs).

Using the most expensive ones (whether they're AC Delco or not) will not make a lick of difference, since the engine is burning oil and they're gonna' get fouled up with oil/carbon pretty soon and cause a misfire.

If your engine IS NOT burning oil: Then buy the original AC Delco platinum tipped spark plugs. This is your best bet to have the best engine performance possible.

Can A Spark Plug Cause A Misfire And Misfire Trouble Code?

Spark plugs that are not firing spark will cause a misfire condition and a misfire code (P0300, P0301, P0302, P0303, P0304, P0305, P0306). There are two specific reasons that can cause this problem:

Internal mechanical problems are causing the spark plugs to get fouled up with gasoline or carbon.

The most likely causes are:

  • The misfiring cylinder is burning oil because its piston oil control rings are severely worn or its cylinder head valves have bad valve stem seals.
  • Fuel injection problems causing the spark plugs to get fuel fouled.
  • Ignition system problems causing a lack of spark to a specific spark plug.
  • Low compression problems in a specific cylinder and causing its spark plug to become fuel fouled or carbon clogged.

Human error causing the spark plug to malfunction.

This is usually caused by spark plug installation problems such as:

  • Breaking the spark plug's insulator (the porcelain part) when tightening the spark plug.
  • Dropping the spark plug and breaking its insulator.
  • Dropping the spark plug and closing the air gap between the center electrode and the side (ground) electrode.
  • The spark plug's air gap is not within the specified range.

More GM 4.2L Test Tutorials

If this tutorial was helpful/informative, you can find a complete list of tutorials here: GM 4.2L Index Of Articles.

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

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Chevrolet Vehicles:

  • Trailblazer 4.2L
    • 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009

GMC Vehicles:

  • Envoy 4.2L
    • 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009