How to Test Misfire Codes (2001-2005 1.7L Honda Civic)

Sooner or later, your 1.7L equipped Honda Civic is going to experience a misfire condition and if it is already, don't despair, 'cause troubleshooting a misfire isn't all that hard.

That's right, it's not hard. There's a method to the madness of troubleshooting a misfire on your 1.7L Honda Civic.

In this article, I'll go into the basics of what causes a misfire condition and I'll also offer you a basic diagnostic strategy to get to the bottom of what's causing the misfire problem.

En Español You can find this tutorial in Spanish here: Cómo Probar Fallas en Encendido (2001-2005 1.7L Honda Civic) (at: autotecnico-online.com).

Let's get started by jumping right into the next subheading...

What Is A Misfire Condition?

A misfire condition happens when one (or more) engine cylinders on your 4 cylinder Honda Civic are not producing power.

As you may already know, each of the 4 cylinders that make up the 1.7L engine in your Honda Civic need fuel, spark, and air (typically compression) to produce power.

When one (or more) of those 4 cylinders misfire, it's because one of those three things is missing from the cylinder (experiencing the misfire).

If your Civic is experiencing a misfire, it's probably doing one or more of the following:

  1. The check engine light (CEL) is on.
  2. The check engine light flashes on and off when the engine is experiencing the misfire.
  3. One or more misfire codes (P0300-P0304) will be stored in your Honda Civic's PCM memory.
    1. P0300 Random Cylinder Misfire.
    2. P0301 Cylinder #1 Misfire.
    3. P0302 Cylinder #2 Misfire.
    4. P0303 Cylinder #3 Misfire.
    5. P0304 Cylinder #4 Misfire.
  4. Sometimes, even tho' the engine is suffering a bona-fide misfire, no misfire codes are registered and no check engine light (CEL) comes on.
  5. Lack of power upon acceleration.
  6. Smell of unburned gas exiting the tail pipe.
  7. Rough idle and may stall.
  8. Cranks but does not start.
  9. Will not pass the emissions tests.
  10. Bad gas mileage.

Although the misfire codes don't tell you what exactly is the cause of the misfire or rough idle condition, there is a way to find out exactly what is causing it.

Let's jump into the next heading and find out what are basic causes of a misfire.

What Causes A Misfire Condition?

The key to successfully diagnosing a misfire code/condition is to keep in mind that the cylinder that's misfiring (‘dead’), on your 1.7L Honda Civic, is missing one of the following:

  1. Air
  2. Fuel
  3. Spark

It's when one of these three things is missing from the mix that the engine in your Honda Civic starts to misfire. Let's look into more specifics:

Ignition System: The majority of misfire codes have their root cause in a failed ignition system component that isn't creating or delivering spark to the affected cylinder.

The usual suspects (that cause a misfire) are:

  1. BAD ignition coil.
  2. BAD spark plugs.
  3. Carbon tracks on the spark plug and spark plug boot.
  4. Oil dripping (from the valve cover) onto the spark plugs and spark plug boots (a very common problem).

Testing all of the ignition system components is not hard and it doesn't require expensive tools or expensive diagnostic equipment.

Fuel System: The Fuel System is responsible for the delivery of fuel. If fuel is missing from any one specific engine cylinder, it will misfire.

Fuel system problems could include some of the following:

  1. BAD fuel injectors.
  2. Broken fuel injector connector (this is a very, very common problem).
  3. Electrical short in the fuel injector wires that are keeping the fuel injector pulse signal from reaching the fuel injector.
    1. This is usually the result of human error and after a major mechanical repair where the wiring harness was damaged.
  4. BAD fuel injection computer not pulsing the fuel injector (this is a very rare condition, but it happens).
  5. BAD fuel pump.

Engine Mechanical Condition: The pistons and valves are the ones that draw air into the engine. Usually all cylinders wear out evenly but every now and then, either thru' lack of maintenance or some mechanical problem, you'll have one or more wear out at an accelerated pace.

To make the long story short, those cylinders (with accelerated wear and tear) to produce a less than average compression value that will cause a misfire condition.

Other issues, that can not be overlooked are vacuum leaks.