How To Do A Cylinder Balance Test (2004-2008 3.5L Malibu)

This tutorial will explain how to do a manual cylinder balance test on the 2004, 2005, 2006, 2007, and 2008 3.5L V6 Chevrolet Malibu.

The cool thing is that you don't need any expensive or exotic test equipment to do a manual cylinder balance test. In this tutorial, I'll explain how to do it with two pieces of vacuum hose and a 12-volt automotive test light.

You can find this tutorial in Spanish here: Cómo Hacer La Prueba Balance De Cilindros (3.5L Chevrolet Malibu) (at: autotecnico-online.com).

What Does A Manual Cylinder Balance Test Do?

To successfully diagnose a misfire condition causing a misfire trouble code, you've got to start with identifying the dead cylinder.

The 2004-2008 3.5L Chevy Malibu usually makes this job easy because its fuel injection computer can identify the misfiring cylinder for you by setting a specific cylinder misfire trouble code.

Unfortunately, this doesn't always happen. There are times the engine is suffering a bonafide misfire but the PCM doesn't set a misfire trouble code to help you identify which of the six cylinders is misfiring.

This is where a manual cylinder balance test comes in handy especially because you don't need any fancy or expensive diagnostic equipment to perform this test. This is the perfect test for the do-it-yourselfer trying to diagnose a hard-to-diagnose misfire condition.

Manual Cylinder Balance Test Essentials

Here's the list of the things that you'll need:

• One 9/32 vacuum hose about 1 1/4" long.
• One 7/32 vacuum hose about 1 3/4" long.
• An automotive 12 Volt test light. This test light cannot be a self-powered or an electronic test light or the manual cylinder balance test won't work.

You're also going to need a helper to help you crank and start the engine while doing the test.

EXAMPLE 1: Test Setup Part 1

To set up the vacuum hoses for the test, this is what you'll need to do:

• Insert and push the 9/32 vacuum hose into the spark plug wire boot as far as it can go. You want to make sure that the vacuum hose goes over the metal terminal of the high tension wire within the boot.
• Insert the 7/32 vacuum hose into the 9/32 vacuum house.
• About one inch of the 7/32 vacuum should be sticking out the 9/32 vacuum hose.
• Connect the spark plug cable (which now has the vacuum hoses inserted into its boot) back to its ignition coil tower.

EXAMPLE 2: Test Setup Part 2

Once the vacuum hoses are inserted, then the next step is to connect the spark plug wire back to its ignition coil tower. As you can see an example above, some of the 9/32 vacuum hose should be exposed.

You'll be touching, with the tip of your 12 Volt test light, this part of the exposed 9/32 vacuum hose to "short" the cylinder.

Here some more details: The vacuum hoses will act as a conduit and transmit the spark from the coil tower to the spark plug wire (when the engine is running).

During the manual cylinder balance test, you'll touch the vacuum hose with the tip of the automotive 12 Volt test light to "kill" (or "short") the cylinder.

The cylinder is "killed" because the spark now goes through the 12 Volt test light to Ground instead of thru' the spark plug wire.

If the cylinder is "live" to begin with, "shorting" its cylinder will cause the engine to shake more (idle rougher). You will clearly see and feel this rougher idle when you touch the vacuum hoses with the 12 Volt test light.

If the cylinder is "dead" to begin with, then "shorting" the cylinder will not have any effect on the engine's idle.

Important Safety Precautions

Doing a cylinder balance test isn't hard but you do have to take some important safety precautions.

PRECAUTION 1: Once the test is set up, the engine has to be started to perform the cylinder balance test. So be careful and stay alert at all times.

PRECAUTION 2: Some folks unplug the spark plug cable from the ignition coil tower to check to see if the cylinder is dead or not. You should avoid this method of testing or you run the risk of damaging the ignition coil. The method I'm explaining in this tutorial uses a piece of vacuum hose between the spark plug cable and the ignition coil tower to short out the cylinder (this method is safe for the ignition coil pack).

PRECAUTION 3: While you're setting up the test, have your helper wait outside of the car to avoid having him accidentally crank and start the engine.