How To Test Engine Compression (1995-1997 2.7L Honda Accord)

An engine compression test can be a challenge to do, but once done, it can provide a wealth of information on the internal condition of the engine.

In this tutorial, I'll explain how the compression test is done in a step-by-step manner.

I'm also going to explain how to interpret your test results to find out if an engine compression problem is causing your 2.7L V6 Honda Accord to not start or if it's causing the engine to misfire.

You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1995-1997 2.7L Honda Accord) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.7L Honda Accord: 1995, 1996, 1997.

Symptoms Of Low Or No Engine Compression

You'll usually see an engine compression problem causing one of two types of problems:

• The engine will not start.
• The engine will start but it will run with a misfire.

By far the most common issue that you'll encounter, when the engine has a compression problem, is a cylinder misfire.

If your Honda is OBD II equipped and the engine compression problem is causing a misfire, then you're going to see the check engine light lit up by one or more of the following trouble codes:

• P0300 Random Cylinder Misfire.
• P0301 Cylinder #1 Misfire.
• P0302 Cylinder #2 Misfire.
• P0303 Cylinder #3 Misfire.
• P0304 Cylinder #4 Misfire.
• P0305 Cylinder #5 Misfire.
• P0306 Cylinder #6 Misfire.

Generally, when an engine compression problem causes a rough idle, you're only going to feel the problem when you come to a stop light. But as soon as you accelerate the engine, the engine feels fine.

You're also gonna' see:

• Bad gas mileage.
• Engine pollutes more and it won't pass an emissions test.

If your 2.7L V6 Honda Accord 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.

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 2.7L V6 Honda Accord.

Which Compression Tester Should I Buy?

There are lot of engine compression testers to choose from and many places to buy them. I'm gonna' make some recommendations to you:

TEST 1: Dry Engine Compression Test

You'll need to remove all of the 6 spark plugs to do an engine compression test.

Before you remove them, the engine should be completely cold. So it it has been running for any length of time, let it cool down completely before removing them.

Removing the spark plugs from a hot engine can damage the spark plug hole threads -this is a nightmare you want to avoid!

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!

These are the test steps:

1. 1

   Disconnect the distributor from its electrical connectors. This will prevent the ignition coil from firing off spark to the spark plug wires during the test.
   
   NOTE: Disconnecting the distributor's electrical connectors is important, since it'll prevent damage to the ignition coil.

2. 2

   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!

3. 3

   Thread 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.

4. 4

   When everything is set up, have your helper to crank the engine. Your job is to keep your eye on the compression tester's gauge.

5. 5

   Once the needle on the gauge stops climbing, have your helper stop cranking the engine.

6. 6

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

7. 7

   Repeat steps 3-6 on the other 5 cylinders.

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

CASE 1: No compression in 2 or more cylinders. This test result tells you that the engine has serious internal problems.

The most common issues would be: Broken timing chain. Or a blown head gasket. Or the engine threw a rod.

CASE 2: Low compression in one or more cylinders. To a certain point, it's normal for the compression to vary a little between cylinders (as the engine accumulates thousands of miles).

But if these values vary too much, then you're gonna' have a bonafide misfire on your hands.

The next step is to do some math to find out if this low compression value is within a normal parameter or not. Go to: Interpreting Your Compression Test Results.

Interpreting Your Compression Test Results

It's not unusual to see engine compression values differ from one another, especially in high mileage engines.

In most cases, and depending on how small or big the difference, nothing happens to engine performance.

When the difference is too big, you'll have a rough idle or a misfire condition on your hands.

To find out if the lower compression value is causing a problem, you need to find out if it's lower than 15% of the highest compression value you got.

You can do this (figuring out the 15%) in one of two ways: You can calculate this 15% difference with pen and paper or you can use my low compression calculator. You can find the low compression calculator here: Online Low Engine Compression Calculator.

If you want to manually calculate the 15% difference, here's what you'll need to do:

• STEP 1: Multiply the highest compression value by 0.15 (this is the decimal value of 15%).
• STEP 2: Round the result to the nearest one (for example: 25.6 would become 26).
• STEP 3: Subtract the result (the number that was rounded) from the highest compression value.
• ANSWER: The result of this subtraction is the lowest possible compression value any cylinder can have.

Now, let me give you a more specific example: Let's say that a 2.7L Honda Accord I'm working on produced the following compression readings:

Cylinder	Pressure
#1	165 PSI
#2	95 PSI
#3	155 PSI
#4	175 PSI
#5	165 PSI
#6	170 PSI

My next step is to do the following calculation:

• STEP 1:  175 x 0.15 = 26.25.
• STEP 2:  26.25 = 26 (rounded to nearest one).
• STEP 3:  175 - 26 = 149.
• ANSWER:  149 PSI. Any cylinder with this compression (or lower) value will misfire.

Since cylinder #2 is only producing 95 PSI, I can now conclude that it's 'dead' and causing a misfire.

To find out if the lowest compression value you got from your engine compression test is within a good range, you'll need to do the same calculation. Of course, you'll need to use the highest compression value you got and not the one in the example.

Once you've found the 'dead' cylinder, the next step is to find out what's causing the low compression value. For this step, go to: TEST 2: Wet Engine Compression Test.

TEST 2: Wet Engine Compression Test

A low or zero cylinder compression value is generally caused by one of two things:

• The cylinder's piston compression rings are worn.
• The cylinder's cylinder head valves are worn or damaged.

Thankfully, we don't need to tear the engine down to find out. We can do a 'wet' compression test instead.

This test simply involves adding about 2 tablespoons of engine oil to the cylinder with low or zero PSI compression and retesting its compression.

If the compression value increases, then you can conclude that the low or zero compression value is due to bad piston rings.

If the compression value does not increase, then you can conclude that the problem lies in the cylinder head valves.

OK, let's start:

1. 1

   Add a small amount of engine oil to the cylinder that reported low compression or no compression in the 'Dry' compression test.
   
   The amount should be about 1 to 2 tablespoons of oil.

2. 2

   Install the compression tester onto the cylinder.
   
   Do not use any type of tool to tightened the compression tester. Hand tight is fine.

3. 3

   When all is set up, have your helper crank the engine while you observe the gauge.

4. 4

   Once the needle on the gauge stops climbing, have your helper stop cranking the engine.

5. 5

   You'll get one of two results:
   
   1.) The compression value will go up (from the one you recorded before).
   
   2.) The compression value will stay the same.

6. 6

   Repeat steps 1-4 on any other cylinder with a low compression test result.

Let's examine your test results:

CASE 1: The compression value shot up. This tells you that that cylinder's piston compression rings are worn out and are behind the low compression test result you got in TEST 1.

CASE 2: The compression value stayed the same. This confirms that that cylinder's valves are behind the low to 0 PSI compression result you obtained in TEST 1.

More 2.7L V6 Honda Accord Tutorials

You can find a complete list of 2.7L V6 Honda Accord tutorials in this index:

• Honda 2.7L Index of Articles.

Here's a small sample of the tutorials you'll find in the index:

• Ignition System Wiring Diagram (1995-1997 2.7L Honda Accord).
• How To Test The Head Gaskets (1995-1997 2.7L Honda Accord).
• P0420 -What Does It Mean? (1996-1997 2.7L Honda Accord).
• How To Test The Ignition System (1995-1997 2.7L Honda Accord).