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.
Contents of this tutorial:
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.
Tools You'll Need:
- Compression Gauge Tester.
- A Helper
- Pen and Paper
Symptoms Of Low Or No Engine Compression
You'll usually see an engine compression problem causing one of two types of problems.
1) Either the engine will not start or 2) 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 two recommendations to you:
1) Which one to buy: The engine compression tester that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it does not come with a case to store it in.
Engine Compression Gauge Testers
2) Where to buy: You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!
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:
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.
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!
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.
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.
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.
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 bona-fide 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.