How To Test Engine Compression (2004-2006 2.8L Chevrolet Colorado, GMC Canyon)

Testing the engine compression on the 2004-2006 2.8L Chevrolet Colorado or GMC Canyon is easy because the spark plugs are accessible.

So if you need to test the engine's compression, this tutorial will explain how to perform the engine compression test step-by-step.

You'll quickly determine if an engine compression problem is causing a cylinder misfire problem or an engine no-start problem.

You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (2004-2006 2.8L Chevrolet Colorado, GMC Canyon) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 2.8L Chevrolet Colorado: 2004, 2005, 2006.
• 2.8L GMC Canyon: 2004, 2005, 2006.

Symptoms Of Low Or No Engine Cylinder Compression

Generally, engine compression problems cause one of two issues:

1. A cylinder misfire problem.
2. An engine no-start problem.

If the engine compression problem is causing a cylinder misfire problem, you'll see one or more of the following diagnostic trouble codes:

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

Besides a misfire trouble code illuminating the check engine light, you'll see one or more of the following symptoms:

• Blue smoke coming out of the tailpipe.
• Rough engine idle that disappears when you accelerate the engine.
• Bad fuel mileage.

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: Finding The Dead Cylinders

To get going, we're going to test the compression of all four cylinders.

Once you've gotten the compression values, the next section will help you interpret the results to find out if you got a problem on your hands or not.

If you don't have an engine compression tester, you can rent one from your local auto parts store for a small deposit (they'll return it to you once you return the tool) or buy one online.

You can check my compression tester recommendations here: Which Compression Tester Should I Buy?

IMPORTANT: Do not remove the spark plugs if the engine has been running for any amount of time. Removing the spark plugs from a hot engine risks damaging the spark plug hole threads in the aluminum cylinder heads.

OK, these are the test steps:

1. 1

   Unplug and remove all four ignition coils.

2. 2

   Remove the spark plugs. Remember, the engine can not be hot!
   
   When removing the spark plugs, be careful not to drop any of them on the floor, or you run the risk of having the spark plug's porcelain insulator crack and then you'll have a misfire on your hands.

3. 3

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

4. 4

   Have your helper crank the engine till the needle on the compression gauge stops climbing.

5. 5

   Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.

6. 6

   Release the pressure on the gauge and repeat the test one more time.

7. 7

   Repeat steps 3 thru 6 on the remaining cylinders.

Let's examine your test results:

CASE 1: One or two cylinders had a much lower compression value than the others. This could be normal or it could be a problem.

To find out if these low engine compression values are causing an engine performance issue, go to: Interpreting The Compression Test Results.

CASE 2: Three or more cylinders had almost no compression or 0 PSI compression. The engine is not gonna' start with this type of compression test result and usually indicates a severe internal engine problem.

I recommend doing a wet compression test on these cylinders to find out if the problem is in the block or cylinder head. Go to: TEST 2: Wet Engine Compression Test.

CASE 3: The compression value of all 4 cylinders was similar and above 120 PSI. This is the correct and expected test result.

Interpreting The Compression Test Results

Depending on the engine's mileage, the cylinder compression values may differ from one another.

To a certain point, a low compression value will not cause engine drivability or an engine performance problem.

But if the variation between the compression values is beyond a specific range, you'll have a cylinder misfire problem.

The rule of thumb is that if a low compression value that's lower by 15% or more than the highest one, then that low compression cylinder will experience a misfire.

How do you figure this out? You can find out by using my online low compression calculator here:

• Online Low Engine Compression Calculator.

You can also calculate this 15% difference manually.

To understand how to figure out this 15% thing manually, I'll use the following compression test results:

• Cylinder #1 175 PSI.
• Cylinder #2 165 PSI.
• Cylinder #3 160 PSI.
• Cylinder #4 120 PSI.

The next step is to do the following math:

• Multiply .15 (15%) by the highest value: 175 x 0.15. This gives us 26.25, but we'll round it out to 26.
• Next, we subtract 26 from 175: 175 - 26 = 144.
• So now we know that the lowest possible compression value is: 144 PSI.

This means that cylinder #4, which has a compression value of 120 PSI, is the one causing the misfire because it's below the 144 PSI minimum.

Once we'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 wet compression test will help determine if the low or 0 PSI compression value you got in TEST 1 is caused by the affected cylinder's intake/exhaust valves or worn piston rings.

The cool thing is that you don't need to tear the engine apart to find out what's causing the problem.

You can easily determine the cause of the issue by doing a wet compression test (on the affected cylinder or cylinders).

These are the test steps:

1. 1

   Add 1 or 2 tablespoon of engine oil in the cylinder you need to retest. I suggest using a small and long funnel so that the oil will reach the inside of the cylinder.

2. 2

   Install the compression gauge on the cylinder you just added oil to.

3. 3

   Have your helper crank the engine till the needle stops climbing on the compression gauge.

4. 4

   You'll see one of two results:
   
   1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
   
   2.) The needle will not move at all or stay at the same number you recorded earlier.

5. 5

   Write the compression value down.

6. 6

   Repeat steps 1 thru' 5 on any other cylinder you need to check.

Let's examine your test results:

CASE 1: The compression value of the cylinder you added oil to increased. This confirms that the cylinder's low compression value is due to worn compression rings on its piston.

CASE 2: The compression value of the cylinder you added oil to DID NOT increase. This tells you that the low compression value you registered in TEST 1 is due to the cylinder having worn or damaged cylinder head valves.

More 2.8L Chevrolet Colorado (GMC Canyon) Tutorials

You can find a complete list of 2.8L Chevrolet Colorado (GMC Canyon) tutorials and wiring diagrams here:

• GM 2.8L Vortec 4-Cylinder Index of Articles.

Here's a list of articles you'll find there:

• How To Test The Electronic Throttle Body (2004-2006 2.8L Chevrolet Colorado, GMC Canyon).
• APP Sensor Tests (2004-2006 2.8L Chevrolet Colorado, GMC Canyon).
• Blown Head Gasket Tests (2004-2006 2.8L Chevrolet Colorado, GMC Canyon).
• TAC Throttle Body Wiring Diagram (2004-2006 2.8L Chevrolet Colorado, GMC Canyon).