How to Test engine compression (Honda 3.0L)

Testing the compression of all 6 cylinders on your Honda/Acura 3.0L V6 is not hard. In this tutorial I'll show you how to do it in a step-by-step way and more importantly, I'll show you how to interpret your compression test results to see if there's a problem or not.

Here are the contents of this article at a quick glance:

  1. Symptoms of Low or No Engine Compression.
  2. The ‘Dry’ Engine Compression Test.
  3. Interpreting the Results of the Engine Compression Test.
  4. ‘Wet’ Engine Compression Test.
  5. Which Compression Tester Should I Buy?
  6. Related Test Articles.

Tools You'll Need:

  1. Compression Gauge Tester.
  2. A Helper
  3. Pen and Paper

Symptoms of Low or No Engine Compression

You can pretty much categorize the symptoms into 2 basic categories:

  1. Your Honda is gonna' start but run rough (better known as running with a misfire).
  2.      -OR-
  3. Your Honda is gonna Crank but Not Start.

Let me go into more details about both conditions:

Engine Starts but Runs with a Misfire:

  1. Also known as an engine miss, rough idle condition.
    1. Usually caused by very low compression in one cylinder or...
    2. Uneven engine compression that varies more than 15% across all 4 cylinders.
  2. Check Engine Light on with misfire codes (if your vehicle is 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. BAD gas mileage.
    1. This is caused by the simple fact that the engine is now running on 3 cylinders, which requires those 3 to work harder to move the vehicle.
  4. Engine pollutes more.
    1. This is also caused by the simple fact that the engine is now running on 3 cylinders, which now has to compensate for the ‘dead’.

If your 3.0L V6 Honda equipped vehicle is NOT OBD II equipped, you won't have any codes lighting up the check engine light, but you'll definitely feel a rough idle condition.

Your Honda won't start:

This usually is caused by having all of the 6 cylinders with no compression. When this happens, you'll see:

  1. The engine cranks very fast.
    1. This fast cranking speed is very noticeable.
  2. The Ignition System is sparking all 6 spark plugs.
    1. This tells you that the No Start Condition is not caused by a fault in the Ignition System.
  3. The fuel injectors spray fuel.
    1. You can confirm this with a Noid Light test.
    2. Also, you can confirm this, although indirectly, by removing the spark plugs and checking to see if they are fuel soaked (fuel fouled).
  4. Fuel pump is working and providing pressure.
  5. The most common causes of no compression on 2 or all 4 cylinders are:
    1. Blown head gasket.
    2. Broken timing belt.
    3. Engine thru' a rod.

OK, having covered the most common scenarios of low compression and no compression, let's get testing to see if this is the case on your 3.0L V6 Honda equipped vehicle.

The ‘Dry’ Engine Compression Test

How to Test Engine Compression (Honda 3.0L)

OK, this is what you signed up for! Now, if you don't have compression tester... you can run down to your local auto parts store and buy one there.

If you live near an AutoZone or an O'Reilly auto parts store, you can rent one from them (they'll rent it to you for free, after you leave them a cash deposit for the tool, which you'll get back once you return it).

If you need help deciding where to buy one or which one to buy, take a look at my recommendations: Which Compression Tester Should I Buy?.

IMPORTANT: You'll be working around a cranking engine, so you have to be careful and stay alert at all times. Think safety all of the time!

This is what you'll need to do:

  1. 1

    If the engine starts, let it warm up for about 10 to 15 minutes, before you start this test (but don't let it get hot!).

    NOTE: If your Honda doesn't start, then don't worry about the engine being warm.

  2. 2

    Disconnect all of the fuel injectors. This will prevent fuel from being injected into the cylinders as you crank the engine.

    This isn't always possible, so if you can't unplug them from their connectors you can remove the fuel pump fuse or the fuel injector fuse located in the fuse box.

  3. 3

    Disconnect the distributor electrical connectors. This will prevent the ignition coil from firing off spark to the spark plug wires (if applicable, since your Honda may be equipped with 6 Coil-on-Plug ignition coils instead of a distributor).

    NOTE: Disconnecting the distributor's electrical connectors is important, since it'll prevent damage to the ignition coil!

  4. 4

    Remove all 6 Coil-on-Plug (COP) ignition coils (if applicable, since your particular Honda may come equipped with a distributor).

  5. 5

    Now, remove all 6 spark plugs. As you're taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plug’s ceramic insulator to break, and this will cause a misfire!

  6. 6

    Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder (this is the spark plug hole closest to the drive belt). Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

Continued in the next page...