How To Test The Engine Compression (2.3L Ranger, Mustang, B2300)

This tutorial will help you do a ‘Dry’ and ‘Wet’ engine compression test on your 2.3L Ford Ranger or Ford Mustang (or 2.3L Mazda B2300).

This tutorial will help you troubleshoot 2 different conditions:

  1. A Rough Idle Condition (Misfire Condition) due to low compression in one or two cylinders.
  2. A No Start due to low or no compression on all 4 cylinders.

There are two different types of compression tests that I'm gonna' show you, one's called a ‘Dry’ compression test and the other is called a ‘Wet’ compression test.

Both of these test will help you determine the health of the engine. The ‘Wet’ compression test will help you further pinpoint a low compression test result to either worn cylinder head valves or worn piston rings.

You can find this tutorial in Spanish here: Cómo Verificar la Compresión del Motor (2.3L Ford) (en:

Symptoms Of BAD Engine Compression

The most obvious symptom, that you're gonna' feel, when one or several cylinders have low compression is a Rough Idle Condition.

Although it doesn't happen all of the time, but if your 2.3L Ford Vehicle is OBD II equipped (1996+), you're gonna' see Misfire Codes stored in the PCM's memory:

  1. Misfire Diagnostic Trouble Codes:
    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.

no compression in all of the cylinders will result in a Cranks but Does not Start Condition. The symptoms you'll see will be:

  1. No Start.
  2. Everything else works, for example:
    1. The fuel pump will activate, so you'll see fuel pressure at specification (if testing with a fuel pressure gauge).
    2. All of the spark plug wires have spark.
    3. If the coil packs are Sparking, then this indirectly proves that the crank sensor is OK too.
    4. The PCM will still activate all of the fuel injectors.

What Tools Do I Need?

The most important tool that you're gonna' need is a compression tester. You can either rent this bad boy from your local auto parts store (Auto Zone, O'reilly, Advanced Auto Parts, etc.), or you can buy one online.

Since the spark plugs need to be removed, you'll need some of the following basic tools:

  1. Ratchet Wrench.
  2. 5/8'' Spark Plug Socket.
  3. Extensions for the Ratchet Wrench.
  4. Motor Oil (for the ‘Wet’ compression test part).
  5. Spark Plug Wire puller.

In case you're needing to buy a compression tester and want to save money by buying it online.. you can shop here: