How Often Should I Change The Spark Plugs (2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009 4.2L Chevrolet TrailBlazer And GMC Envoy)

The spark plugs on your 4.2L Chevrolet TrailBlazer or GMC Envoy are designed to last a very long time.

But as the engine wears and it accumulates lots of miles, you're going to have to replace them at shorter intervals.

Since quite a few things factor into when to replace the spark plugs, in this tutorial I'm going offer you a few suggestions on when to replace them.

En Español You can find this tutorial in Spanish here: ¿Cuándo Debería Reemplazar Las Bujías? (2002-2009 4.2L Chevrolet TrailBlazer) (at: autotecnico-online.com).

What Causes Spark Plugs To Wear Out?

In a nutshell, the spark plug will wear out because of the spark that jumps between its center and side electrode. This spark will wear out even the toughest of materials.

This type of spark plug failure usually happens around a hundred thousand miles of service if you're using the recommended platinum tipped spark plugs.

What usually causes a spark plug to fail long before then, is if your TrailBlazer or Envoy's engine is burning oil and the spark plug accumulates carbon deposits between its electrodes.

These carbon deposits will block the air gap between the electrodes and spark will no longer jump between them.

The end result of this carbon buildup and blockage is a dead cylinder that will cause the engine to misfire. This in turn will cause the check engine light to light up with a misfire trouble code (P0301, P0302, P0303, P0304, P0305, P0306).

When Should I Replace The Spark Plugs?

So when you should replace the spark plugs? -It all depends on if your 4.2L Chevrolet TrailBlazer or GMC Envoy is consuming oil. Here are my recommendations:

If the engine is burning oil: The spark plugs that are in the cylinders burning oil will not give you a service life of around 100,000 miles.

Eventually the engine will start to idle rough or misfire. In most cases you're gonna' have the check engine light lit up with a misfire trouble code.

More than likely, you've got a spark plug that has its air gap (between the center and side electrode) blocked with carbon.

This means you could be replacing the spark plugs in a few months or maybe in a year.

How can you find out if the engine is burning oil? You'll know because:

  1. You have to add oil on a weekly basis to the engine.
  2. You see blue smoke coming out of the tail pipe when you accelerate the engine under load.
  3. You see blue smoke coming out of the tail pipe when you first start up the engine.

If the engine IS NOT burning oil: You'll be able to go almost 100,000 miles before its time to change the spark plugs in your TrailBlazer or Envoy.

The spark plugs on your 4.2 Chevrolet TrailBlazer or GMC Envoy are made with platinum or iridium. These are some of the toughest metals on the planet and they will extend the life of the spark plug tremendously. It's not unusual to see a platinum spark plug service life around 100,000 miles.

But you're only going to see this long spark plug service life if the engine in your Trailblazer or Envoy isn't consuming oil.

Depending on how many miles you put on your vehicle on a yearly basis, you may be replacing the spark plugs anywhere between 3 to 6 years.

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