How To Troubleshoot Misfire Codes (GM 3.1L, 3.4L)

My Vehicle Has OBD II Where Do I Start My Misfire Diagnosis?

The very first thing you have to do is find out is which cylinder is the one misfiring. This usually means connecting a scan tool and reading the misfire codes.

So, if your vehicle does have any of the following misfire diagnostic trouble codes: P0301, P0302, P0303, P0304, P0305, P0306; you would use an illustration like the one in the image viewer to find out which cylinder is the one identified by the misfire code or codes. Here's a list of what cylinder each misfire code identifies:

• P0301 This Misfire Code identifies Cylinder #1.
• P0302 This Misfire Code identifies Cylinder #2.
• P0303 This Misfire Code identifies Cylinder #3.
• P0304 This Misfire Code identifies Cylinder #4.
• P0305 This Misfire Code identifies Cylinder #5.
• P0306 This Misfire Code identifies Cylinder #6.

What Does The Misfire Code Tell Me To Replace?

A very common misconception is that hooking up a scan tool and reading the trouble codes is enough to find out what needs to be replaced.

In the case of misfire codes, these in themselves don't tell you what exactly is wrong or what exactly needs to be replaced. All they're doing is telling you which cylinder is the one that's affected.

It's up to you to do some testing to find out if the problem is due to a bad coil pack, or a bad spark plug wire, or a bad fuel injector, and so on and on. Remember, so many different things can cause a misfire. Here are some of the tests that you'll need to look into:

1. Ignition System Tests: Making sure that the cylinder that the misfire code is identifying is getting spark is the very first thing you have to check. In about 90% of the time, the fault lies in the ignition system.
   
   I have written the perfect article to help find out if the spark plug wires are bad, or if the coil pack is bad, etc.
2. Engine Mechanical Tests: If it turns out that the cylinder misfire problem is not due to missing spark, then I would recommend a compression test.
3. Fuel Injector Test: If it turns out that the cylinder misfire problem is not due to missing spark or low cylinder compression, then I would recommend doing a fuel injector Test.

The cool thing is that you can find out what is wrong and replace just the part or parts that are bad. As mentioned before, this involves the physical testing of the components. In the section: Where Do I Find The Test Articles, you'll find links to specific testing articles that will help you in your misfire diagnostic.

My Vehicle Does NOT Have OBD II Where Do I Start My Misfire Diagnosis?

If your car is not OBD II equipped and does not have the misfire diagnostic capability you still can accurately find out which cylinder is the one that's misfiring (or dead).

The very first thing that you'll have to do is a cylinder balance test. The cylinder balance test will help you to locate which cylinder is the one that's dead.

Now, keep in mind that the cylinder balance test will not tell you what part or parts to replace. It's up to you to do some testing to find out if the cylinder is dead due to a bad coil pack, or a bad spark plug wire, or a bad fuel injector, and so on and on. Remember, so many different things can cause a misfire. Here are some of the tests that you'll need to look into:

• Ignition System Tests: The first thing you have to verify is that the cylinder, that the cylinder balance test identified as dead, is getting spark. This means testing for spark. I can tell you that the problem (of the dead cylinder) almost always has to do with missing spark.
• Engine Mechanical Tests: If it turns out that the cylinder is getting plenty of spark, then the next thing (I would do) is a compression test of the cylinder or cylinders. The compression test is one of the most overlooked tests when troubleshooting a rough idle, misfire condition.
• Fuel Injector Test: If it turns out that the cylinder misfire problem is not due to missing spark or low cylinder compression, then I would recommend doing a fuel injector Test.

You don't have to throw parts at your Chevy (or Olds, Buick, Pontiac) car or mini-van to see if something will solve the problem. With some specific tests you can find the cause of the dead cylinder. In the section: Where Do I Find The Test Articles, you'll find links to specific testing articles that will help you in your misfire diagnostic.

Where Do I Find The Test Articles?

Here are the Test Articles you'll need to get your misfire diagnostic on the road:

1. GM 3.1L & 3.4L Ignition System Tests This article will help you to troubleshoot the coil packs, spark plug wires, ICM, etc. (this info is found at: easyautodiagnostics.com).
2. How To Do A Cylinder Balance Test (GM 3.1L, 3.4L).
3. How To Test Engine Compression (GM 3.1L, 3.4L).
4. How To Test The Fuel Injectors (GM 3.1L, 3.4L).