How To Test Misfire Codes (Honda 3.0L)

Troubleshooting a misfire condition on your 3.0L equipped Honda Accord (Odyssey or Acura CL) can seem quite intimidating and/or near impossible. Especially since quite a few things can cause one or more cylinders to go ‘dead’ such as:

  1. Failed spark plug wires.
  2. Bad distributor cap.
  3. Bad fuel injector.
  4. Bad Coil-on-Plug (COP) ignition coil.
  5. One or more engine cylinders having very low compression.

I could go on about more ‘possible’ bad components... but you get the general idea. The good news is that testing a misfire code, or misfire codes, or a rough idle condition is not that hard and it's something you can do or learn enough to make an informed decision at your auto repair shop.

In this tutorial, I'm going to explain in some detail the most common causes of misfires and misfire codes (P0300, P0301, P0302, P0303, P0304, P0305, P0306 -OBD II equipped) and more importantly, I'm also gonna' offer you a simple diagnostic strategy that I'm certain will help you ‘nail down’ the cause of the misfire condition, misfire code, or rough idle condition your Honda is experiencing.

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

What Is a Misfire Condition?

In English you and I can understand... a misfire condition describes a situation in which one or more cylinders of your Honda's 3.0L V-6 are not functioning. It can be said that this cylinder or cylinders are ‘dead’ either because the cylinder or cylinders are missing fuel, or spark, or air.

Here are a few other symptoms you'll see with a misfire:

  1. The Check Engine Light will be on.
  2. One or more Misfire Codes (P0300-P0306) will be stored in your pick up's PCM memory (if OBD II equipped).
    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.
    6. P0305 Cylinder #5 Misfire.
    7. P0306 Cylinder #6 Misfire.
  3. Sometimes, even tho' your OBD II equipped Accord is suffering a bona-fide misfire, no misfire codes are registered and no Check Engine Light (CEL) comes on.
  4. Lack of power upon acceleration.
  5. Smell of unburned gas exiting the tail pipe.
  6. Rough idle and may stall.
  7. Cranks but does not start.
  8. Will not pass the emissions tests.
  9. 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.

One of the most important things you need to know, to successfully diagnose a misfire or rough idle condition, is what causes a misfire. Let's go to the next subheading and find out.

What Causes A Misfire Condition?

In a nutshell, each engine cylinder in your 3.0L 6 cylinder Honda Accord (Odyssey or Acura CL) needs 3 things to output power, these are:

  1. Air
  2. Fuel
  3. Spark

It's when one of these three things is missing from the mix that the engine in your 3.0L Honda starts to misfire. Let's look into more specifics:

Ignition System: The ignition system is responsible for the production and delivery of Spark. The Ignition System is usually the culprit behind most misfires. Your specific 3.0L V6 may have either a distributor-type ignition system or a distributor-less one.

In a distributor-less ignition system, you'll have 6 individual ignition coils sitting right on top of the spark plug. Although both of these systems are physically different, they both are tasked with creating and delivering spark to the spark plugs.

Distributor Type System: In this type of ignition system setup, the usual suspects (that cause a misfire) are:

  1. BAD spark plugs.
  2. Carbon tracks on the spark plug and spark plug boot.
  3. BAD distributor cap.
  4. BAD spark plug wires.
  5. Oil dripping (from the valve cover) onto the spark plugs and spark plug boots.

Distributor-less Type System: In this type of ignition system setup, you're gonna' have an individual ignition coil sitting on top of the spark plug. The usual suspects (that cause a misfire) are:

  1. BAD spark plugs.
  2. Carbon tracks on the spark plug and COP ignition coil boot.
  3. BAD Coil-on-Plug (COP) ignition coil.
  4. Oil dripping (from the valve cover) onto the spark plugs and COP ignition coil boots.

The following tutorial should help you with testing the COP ignition coils:

  1. How To Test The Coil on Plug Ignition Coil (Honda 3.0L) (at: easyautodiagnotics.com).
  2. Carbon Tracks Are A Common Cause Of Ignition Misfires (at: easyautodiagnotics.com).

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.
  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 cylinder head 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. If you've never done an engine compression test... the following tutorial will help:

  1. How To Test Engine Compression (Honda 3.0L).

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