Troubleshooting a misfire problem isn't difficult nor complicated. In this tutorial, I'm going to share some of my experience on how to diagnose a misfire issue.
I'll answer some of the most commonly asked questions about a misfire problem in the process.
Contents of this tutorial at a glance:
APPLIES TO: This tutorial applies to the following vehicles:
- 3.1L V6 Buick Century: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005.
- 3.1L V6 Buick Regal: 1994, 1995, 1996.
- 3.1L V6 Buick Skylark: 1994, 1995, 1996.
- 3.1L V6 Oldsmobile Achieva: 1994, 1995, 1996, 1997, 1998.
- 3.1L V6 Oldsmobile Cutlass: 1997, 1998, 1999.
- 3.1L V6 Oldsmobile Cutlass Ciera: 1994, 1995, 1996.
- 3.1L V6 Oldsmobile Cutlass Supreme: 1993, 1994, 1995, 1996, 1997.
What Is A Misfire?
An engine misfire refers to a problem in which one or more cylinders do not produce power.
To be a bit more specific, a misfire occurs due to the incomplete combustion of the air/fuel mixture within a cylinder (or cylinders).
In some cases, the combustion of the air/fuel mixture (within the cylinder) does not happen at all.
What Are The Symptoms Of A Misfire?
A cylinder misfire can cause a wide range of symptoms. Here's a list of some of the symptoms you'll see:
- Rough idle.
- Bad gas mileage.
- Extended engine cranking (engine takes longer than usual to start).
- A heavier than normal exhaust smell coming out of the tailpipe.
- The engine is not as peppy as it used to be.
- Hesitation when you accelerate the vehicle on the road.
- Misfire trouble codes lighting up the check engine light (OBD II):
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
What Causes A Misfire Problem?
A misfire occurs when a cylinder does not receive one of the following to start and complete the combustion process:
- Air (compression).
- Fuel.
- Spark.
Quite a few components are involved in delivering air, fuel, and spark (to the cylinders for the combustion process to take place).
When one of these components fails, the engine will suffer a cylinder misfire.
Here's a basic list of the faulty components that could cause a misfire:
- A bad spark plug.
- A bad ignition coil pack.
- A bad fuel injector.
- A clogged fuel injector.
- A cylinder (or cylinders) with low engine compression. This could be caused by:
- Bad intake/exhaust valves.
- Bad piston rings.
- A bad intake manifold gasket.
How Do You Fix A Misfire?
The most important step in troubleshooting and resolving a misfire problem is identifying the 'dead' cylinder(s).
Once the 'dead' cylinder has been identified, the next step is to find out what it's missing. Is it missing spark? Is it not producing enough compression? Is it not receiving fuel?
Is spark missing?
To find out if the cylinder is not receiving spark, you'll need to:
- Remove and visually inspect the cylinder's spark plug for any damage or any condition that would keep the spark from jumping from its center electrode to its side electrode.
- Check that the spark plug wire (that connects to the cylinder's spark plug) is sparking with a dedicated spark tester.
- Check that the ignition coil tower (that connects to the cylinder's spark plug wire) is sparking.
The following tutorial will help you diagnose the ignition coil packs and the spark plug wires:
- How To Test The Ignition Coil Packs (GM 3.1L, 3.4L) (at: easyautodiagnostics.com).
Is compression missing?
You'll need to do an engine compression test find out if the 'dead' cylinder is not producing compression.
The following tutorial will help you do an engine compression test, and more importantly, it'll explain how to interpret your test results:
Is fuel missing?
The 'dead' cylinder's fuel injector could be clogged or faulty. And finding out can be challenging since the fuel injectors are under the intake manifold plenum.
There are quite a few ways to test a fuel injector. Unfortunately, most of them involve expensive diagnostic equipment. If you have the diagnostic equipment or can get it, then this is your next step.
Personally, I've used a process of elimination to pinpoint a bad fuel injector that has been very effective on the GM 3.1L V6 engine. This is what I do:
- I make sure that the 'dead' cylinder is receiving spark.
- This involves confirming that the spark plug wire is good and delivering spark.
- I also remove the spark plug and confirm that it is in good shape.
- I test the cylinder's compression and make sure it's within an acceptable range (compared to the others).
- I check the intake manifold gasket. Specifically:
- I check if it's leaking coolant.
- I also check if it's leaking vacuum (very important).
Only after eliminating the ignition system, the cylinder's compression, and the intake manifold gasket can I conclude that the cause of the misfire problem is the fuel injector.
I then remove the plenum and resistance-test the fuel injector to see if it has suffered an internal short-circuit problem. My next step is to replace it.
More 3.1L V6 Buick, Oldsmobile Tutorials
You can find a complete list of 3.1L V6 Buick (Oldsmobile) tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test Engine Compression Test (3.1L V6 Buick, Oldsmobile).
- How To Test A Blown Head Gasket (3.1L V6 Buick, Oldsmobile).
- How To Test The Fuel Pump (3.1L V6 Buick, Oldsmobile).
- How To Test The 24X Crankshaft Position Sensor (1995-1997 3.1L V6 Oldsmobile Cutlass Supreme).
If this info saved the day, buy me a beer!
