How To Do A Cylinder Balance Test (GM 3.1L, 3.4L)

Trying to find out which cylinder is the one misfiring can be a little difficult if the PCM (Powertrain Control Module= Fuel Injection Computer) does not set a misfire code.

Unplugging one spark plug wire at a time (while the engine is idling) to see if the engine will stumble or not is the WORST thing you can do (to find the engine cylinder that's missing). Why? Well, not only do you run the risk of shocking yourself... but this could fry the coil pack the wire is connected to.

Well, this article will show you a way to do a cylinder balance test without using expensive diagnostic equipment or diagnostic software on the 2.8L, 3.1L, or 3.4L GM V6 engine with the coil pack ignition system. I have used this test for as long as I have been working on cars and it has saved me hundreds of troubleshooting hours.

To help you navigate this article a little easier, here are its contents at a quick glance:

  1. What Tools Do I Need?
  2. How Can this Test Help Me If I Have a Misfire But No Misfire Codes!
  3. The Cylinder Balance Test.
  4. Coil Pack Assembly is Under Exhaust Manifold.
  5. Related Test Articles.

En Español You can find this tutorial in Spanish here: Cómo Hacer La Prueba Balance De Cilindros (3.1L, 3.4L V6 GM) (at:

What Tools Do I Need?

You're only gonna' need three things: 1.) A 12 Volt test light. 2.) Two small pieces of vacuum hose and 3.) A helper to help you crank the car or mini-van.

The test light HAS to be a simple (non-powered) 12 Volt automotive test light. This is important because if you use any type of electronic or self-powered test light... this cylinder balance test is not gonna' work.

How Can this Test Help Me If I Have a Misfire But No Misfire Codes!

Before I jump into the test (in the next page), I want to emphasize that this cylinder balance test will help when:

CASE 1: Your OBD II car with misfire diagnostics, the PCM (Powertrain Control Module= Fuel Injection Computer) can not figure out which cylinder is the one misfiring. Sometimes, you can drive the vehicle till its out of gas, and the PCM still will not set the appropriate misfire code to identify the specific cylinder that's missing.

CASE 2: Your car (or mini-van) does not have OBD II misfire capability because it's older than 1995 (in these older cars, the PCM does not have misfire diagnostic capabilities) and so it's definitely NOT gonna' help you to find out which cylinder is the one misfiring.

Well, my friend, this is where this test is gonna' save the day. The test I'm gonna' show you is the best way to find out which cylinder is misfiring without doing something as scary and risky as pulling a spark plug wire off of the spark plug (while the engine is idling) or buying expensive diagnostic software and equipment.

Once you find out what cylinder or cylinders are missing (‘dead’/misfiring)... you can proceed to troubleshoot the cause. OK, enough of my yakking, let's turn the page and we'll get this show on the road!