How To Test The Engine Compression (1.7L Honda Civic)

What makes testing the compression of the 1.7L Honda Civic engine easy is the spark plugs are very accessible (since you'll need to remove them for the test).

In this tutorial, I'll explain how to test the engine compression and, more importantly, how to interpret its test results.

With your test results, you'll quickly find out if a compression problem is causing an engine no-start problem or an engine misfire problem.

APPLIES TO: This tutorial applies to the following vehicles:

• 1.7L Honda Civic DX: 2001, 2002, 2003, 2004, 2005.
• 1.7L Honda Civic EX: 2001, 2002, 2003, 2004, 2005.
• 1.7L Honda Civic GX: 2001, 2002, 2003, 2004, 2005.
• 1.7L Honda Civic HX: 2001, 2002, 2003, 2004, 2005.
• 1.7L Honda Civic LX: 2001, 2002, 2003, 2004, 2005.

Symptoms Of Low Or No Engine Compression

Engine compression problems usually cause one of two issues:

• An engine no-start problem.
• The engine starts but runs with a misfire or a rough idle condition.

If the engine does start, you'll see one or more of the following symptoms:

• Bad gas mileage.
• A heavier exhaust smell coming out of its tailpipe.
• Engine is not as peppy as it was once.
• Rough idle that goes away as soon as you accelerate the engine.
• One or more of the following misfire trouble codes:
  • P0300: Random Cylinder Misfire.
  • P0301: Cylinder #1 Misfire.
  • P0302: Cylinder #2 Misfire.
  • P0303: Cylinder #3 Misfire.
  • P0304: Cylinder #4 Misfire.

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 two recommendations:

TEST 1: 'Dry' Engine Compression Test

You'll need to remove the spark plugs to test the engine's compression. When removing them, check for the following:

• Spark plug tube full of engine oil.
• Spark plug and spark plug boot soaked in engine oil.
• Any apparent damage or wear on the spark plug boot and spark plug.

If you find engine oil in the spark plug tube, replace the valve cover gasket and spark plug tube seals. You'll also need to replace any component that is oil-soaked.

If you don't have an engine compression tester, you can run down to your local auto parts store and either buy one or borrow one from them.

You can also buy one online. You can check out my recommendations here: Which Compression Tester Should I Buy?

IMPORTANT: Do not remove the spark plugs if the engine is hot. If the engine has been running for any amount of time, let it cool down completely before removing the spark plugs.

CAUTION: Take all necessary safety precautions. The engine has to be cranked to perform the engine compression test. Be careful and think safety all the time!

Okay, these are the test steps:

1. 1

   Disable the fuel system by removing the fuel pump relay.
   
   This will prevent fuel from being injected into the cylinders as you crank the engine.

2. 2

   Remove the COP ignition coils.

3. 3

   Remove the 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!

4. 4

   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).
   
   IMPORTANT: Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

5. 5

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

6. 6

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

7. 7

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

8. 8

   Repeat steps 4 thru' 7 on the remaining cylinders.

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

CASE 1: Low or no compression in 2 or all cylinders. This test result indicates a serious internal problem.

The most common issues would be:

• Blown head gasket.
• Broken timing belt.
• Engine threw a rod.

CASE 2: Low compression in one or more cylinders. Up 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 uncommon for the compression value of each cylinder to vary from one another. Up to a certain point, a difference between compression values won't cause an engine performance problem.

But if the compression values vary by more than 15%, you'll have a rough idle issue or a misfire problem.

You can do this (figuring out the 15%) in one of two ways:

1. You can calculate this 15% difference with pen and paper.
2. You can use my low compression calculator. You can find it here: Online Low Engine Compression Calculator (at: easyautodiagnostics.com).

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 I got the following compression readings:

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

One of two things will cause a low cylinder compression value:

1. The affected cylinder's intake/exhaust valves are damaged or worn out.
2. The affected cylinder's piston rings are damaged or worn out.

Thankfully, you don't need to take the engine apart to find out since a 'wet' compression test will easily tell you where the problem is.

In a wet compression test, you add about two tablespoons of engine oil to the cylinder with low compression and then retest its compression.

If the cylinder's compression value increases, you can conclude that the low compression value is due to piston ring problems.

If the compression value does not increase, you can conclude that the problem is due to bad intake or exhaust valves.

OK, let's get started:

1. 1

   Add a small amount of engine oil to the cylinder that reported low compression or no compression in the 'dry' compression test.
   
   You don't have to add a lot of oil. 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 tighten the compression tester. Hand tight is fine.

3. 3

   When all is set up, have your helper crank the engine.

4. 4

   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.

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

CASE 1: The compression value shot up. This test result confirms the low compression value is caused by bad piston compression rings.

CASE 2: The compression value stayed the same. This test result confirms the low compression problem is caused by worn or damaged cylinder head valves.

More 1.7L Honda Civic Tutorials

You can find a complete list of 1.7L Honda Civic tutorials in this index:

• 1.7L Honda Civic Index Of Articles.

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

• How To Test The Crank Sensor (2001-2005 1.7L Honda Civic).
• Maintenance Required Light Reset (2001-05 1.7L Honda Civic).
• How To Do A Cylinder Balance Test (2001-2005 1.7L Honda).
• How To Test The TP Sensor (2001-2005 1.7L Honda Civic).