How To Test Engine Compression (1998-2007 3.0L V6 Honda Accord)

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.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L V6 Honda Accord: 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.0L V6 Acura CL: 1997, 1998, 1999.

Symptoms Of Low Or No Engine Compression

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

• Your Honda is gonna' start but run rough (better known as running with a misfire).
•      -OR-
• 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.
   • Usually caused by very low compression in one cylinder.
   • Or uneven engine compression that varies more than 15% across all 6 cylinders.
2. Check engine light is on with misfire codes (if your vehicle is OBD II equipped):
   • 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.
3. Bad gas mileage.
   • This is caused by the simple fact that the engine is now running on less than 6 cylinders, which requires those cylinders to work harder to move the vehicle.
4. Engine pollutes more.
   • This is also caused by the simple fact that the engine is now running on less than 6 cylinders, which now has to compensate for the 'dead' cylinder or cylinders.

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.

NOTE: If you're troubleshooting an engine no-start problem and engine compression is not behind it, see this guide for more diagnostic tips:

• How To Troubleshoot A No Start (1998-2007 3.0L V6 Honda Accord).

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.
   • This fast cranking speed is very noticeable.
2. The ignition system is sparking all 6 spark plugs.
   • This tells you that the no-start condition is not caused by a fault in the ignition system.
3. The fuel injectors spray fuel.
   • You can confirm this with a Noid Light test.
   • 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 6 cylinders are:
   • Blown head gasket.
   • Broken timing belt.
   • Engine threw 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.

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 these recommendations to you:

The 'Dry' Engine Compression Test

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

   Disable the fuel system by removing the fuel pump fuse.

2. 2

   If your Honda has an ignition distributor, disconnect it from its 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!

3. 3

   Remove all 6 ignition coils (if your particular Honda is equipped with a COP ignition coil ignition system).

4. 4

   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!

5. 5

   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.

6. 6

   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.

7. 7

   Once the needle on the gauge stops climbing, have your helper stop cranking the engine.
   
   Write down the compression value on a piece of paper. Include the number of the cylinder this reading belongs to.

8. 8

   Repeat steps 1 thru' 7 on the remaining cylinders.

Let's analyze your test results:

CASE 1: 0 PSI compression in all 6 cylinders. This test result tells you that the engine has serious internal problems.

The most common issues would be:

• Broken timing belt.
• Blown head gasket.
  • To further test this, I recommend the following tutorial: How To test For A Blown Head Gasket (Honda 1.5L, 1.6L) (NOTE: This info will apply to your Honda 3.0L equipped vehicle).
• Engine threw a rod.

CASE 2: One or more cylinders had a low compression value compared to the others. This could be normal or it could be causing a problem.

To find out the next step is do some math and see if the low compression value is lower by more than 15% of the highest compression value you got. To find a detailed explanation of this calculation go to: Interpreting The Results Of The Engine Compression Test.

CASE 3: All six compression values were similar and above 120 PSI. This lets you know that a compression problem is not behind the no-start or misfire problem you're trying to troubleshoot.

Interpreting The Results Of The Engine Compression Test

If you got a low compression reading, the next step is to find out if this reading is varying by more than 15% than the other cylinders (because if it is varying by more than 15%, then this cylinder is considered 'dead'), this is how you can find out:

1. Grab a calculator and multiply the highest compression reading that you recorded by 0.15.
   • So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X 0.15 gives you 26 (25.5 rounded off).
2. Now, the next step is to subtract 26 from 170, which gives us 144 PSI.
3. So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this and that engine cylinder will misfire.

Now, so that this calculation can make more sense to you, let's say that my Honda gave me the following compression readings:

• Cylinder #1 165 PSI.
• Cylinder #2 170 PSI.
• Cylinder #3 175 PSI.
• Cylinder #4    30 PSI.
• Cylinder #5 165 PSI.
• Cylinder #6 175 PSI.

The next step is to do the math: 175 x 0.15= 26, 175-26= 149. So, now I know that cylinder #4 is the one causing the misfire!!

Now that you've found the cylinder with the low compression, the next step is to see if this low compression is caused by worn cylinder head valves or worn piston rings. For this test, go to: TEST 2: 'Wet' Engine Compression Test.

TEST 2: 'Wet' Engine Compression Test

After confirming that you do have a cylinder or cylinders with low compression (or with 0 PSI compression), the next step is to do a 'wet' compression test.

To do a 'wet' compression test, all we have to do is add about two tablespoons of oil to the confirmed 'dead' engine cylinder or cylinders.

Depending on the compression test result of the cylinder you added oil to, you'll be able to determine if the low compression reading you recorded in the 'dry' compression test is caused by worn piston rings or worn cylinder head valves.

OK, this is what you need to do:

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 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 your test results:

CASE 1: The compression value shot up. This tells you that the piston compression rings are worn out and thus the problem is in the bottom end (block) of the engine in your 2.7 or 3.0L Honda.

The reason why is that the oil you just added helped the piston rings seal better, thus causing the compression reading to rise.

CASE 2: The compression value stayed the same. This confirms that the problem is in the cylinder head valves.

The reason for this is that nothing, not even the engine oil, can help the cylinder head valves seal the compression in. So, after adding oil and retesting the compression, the compression value doesn't increase, then you now know that the problem is in the cylinder head valves.

Related Test Articles

You can find all of the 3.0L V6 Honda equipped vehicle articles here: 3.0L V6 Honda Accord Index Of Articles.

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

• How To Troubleshoot A No Start (1998-2007 3.0L V6 Honda Accord).
• How To Test For A Broken Timing Belt (1998-2007 3.0L V6 Honda Accord).
• How To Test The Coil-On-Plug Ignition Coil (2000-2003 3.0L V6 Honda Accord).
• How To Test The Ignition Coils (2003-2007 3.0L V6 Honda Accord).