How To Test The Engine Compression (1989-1997 2.3L Ford Ranger)

This tutorial will help you perform a dry and wet engine compression test on your 1989-1997 2.3L Ford Ranger.

You'll be able to troubleshoot these two engine performance problems:

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 four cylinders.

The dry and wet engine compression tests will help you determine the internal condition of the engine. The wet compression test will help you 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) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.3L Ford Ranger: 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.
• 2.3L Mazda B2300: 1995.

Symptoms Of Bad Engine Compression

The most obvious symptom you'll experience when one or more cylinders have low compression is a rough idle condition or an engine cylinder misfire issue.

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:

Although it doesn't always happen, if your 2.3L Ford Ranger is equipped with OBD II (1996+) you'll see misfire codes stored in the memory of the PCM:

• Misfire Diagnostic Trouble Codes:
  • P0300: Random Cylinder Misfire.
  • P0301: Cylinder #1 Misfire.
  • P0302: Cylinder #2 Misfire.
  • P0303: Cylinder #3 Misfire.
  • P0304: Cylinder #4 Misfire.

No compression in all cylinders leads to a 'cranks but does not start' problem. The symptoms you'll see are:

1. The engine does not start.
2. Everything else works, for example:
   • The fuel pump will activate, so you'll see fuel pressure at specification (if testing with a fuel pressure gauge).
   • All of the spark plug wires have spark.
   • If the coil packs are sparking, then this indirectly proves that the crankshaft position sensor is OK too.
   • The PCM will still activate all of the fuel injectors.

What Tools Do I Need?

The most important tool you'll need is a compression tester. You can either rent it at your local auto parts store (Auto Zone, O'Reilly Auto Parts, Advanced Auto Parts, etc.) or buy it 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.

If you need to buy a compression tester and want to save money, you can shop here:

TEST 1: Dry Compression Test

As you're already aware, the 2.3L four cylinder engine in your Ford Ranger (Mazda B2300) comes equipped with 8 spark plugs.

You don't need to remove all eight to do an engine compression test. Remove only the four spark plugs on the exhaust manifold side of the cylinder head.

IMPORTANT: Do not remove the spark plugs from a hot engine. If the engine is hot, let it cool down before removing the spark plugs.

Let's get testing:

1. 1

   Disable the fuel system. You can easily do this by simply disconnecting the fuel pump relay.
   
   This step is important, so don't skip it. Why? Because it will prevent the PCM from injecting fuel into the cylinders during the compression test.

2. 2

   Disable the ignition system.
   
   You can easily do this by simply disconnecting both coil packs from their electrical connectors.
   
   This step is important since it will prevent damage to the ignition coil packs, so don't skip it.

3. 3

   Remove ONLY the exhaust manifold side spark plugs.
   
   Leave the 4 intake manifold spark plugs in their place.
   
   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!

4. 4

   Install the engine compression gauge into the spark plug hole for the number 1 engine cylinder.
   
   NOTE: Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

5. 5

   When ready, have a helper crank the engine as you observe the needle on the compression tester's gauge.

6. 6

   Have your helper stop cranking the engine once the needle on the gauge stops climbing.

7. 7

   Write down the compression value.
   
   Record this compression reading on a piece of paper. Include the number of the cylinder this reading belongs to.

8. 8

   Now repeat steps 4 thru' 7 on the other cylinders.

Let's take a look at what your test results mean:

CASE 1: You got a reading of 100 PSI or less (less being 0 PSI) on all of the cylinders. This test result tells you that you've got serious engine mechanical problems.

If you have 0 PSI compression on all 4 cylinders it sounds like you have a broken timing belt on your hands. The next step is to remove the timing case cover and check the condition of the timing belt.

What is common when you have a very high mileage engine is low compression across the board. Low usually means anything under 120 PSI (although the service manual says 100 PSI is the minimum). By the time your engine gets to that point, it's also smoking a quart of oil every few days. The other symptoms you'll see is that the idle is very rough.

CASE 2: One or two cylinders gave a low compression reading. This can be normal as not every cylinder delivers the exact same pressure reading. Or those low compression values could cause a problem.

To find out, go to: How To Interpret The Engine Compression Test Results.