How To Test Engine Compression (2.4L Cobalt, HHR, Malibu, G5, G6, Solstice)

In this tutorial, I'm going to show you how to test the engine compression on the 2.4L engine used in the Chevrolet Cobalt, Chevrolet Malibu, Pontiac G5, Pontiac G6.

With the help of this tutorial you'll be able to find out if an engine compression problem is causing your vehicle to not start or if it's behind a misfire problem that's lighting up the check engine light.

APPLIES TO: This tutorial applies to the following 2.4L equipped GM vehicles:

• Chevrolet Cobalt 2.4L: 2006, 2007, 2008.
• Chevrolet HHR 2.4L: 2006, 2007, 2008, 2009.
• Chevrolet Malibu 2.4L: 2008, 2009, 2010, 2011, 2012.
• Pontiac G5 2.4L: 2006, 2007, 2008.
• Pontiac G5 GT 2.4L: 2007, 2008.
• Pontiac G6 2.4L: 2006, 2007, 2008, 2009.
• Pontiac Soltice 2.4L: 2006, 2007, 2008, 2009.

Symptoms Of Low Or No Engine Cylinder Compression

For the most part you're going to see one of two types of problems when the engine is suffering a compression problem.

The most common type of problem you're going to see with a compression problem is low compression in one or two cylinders that's causing the engine to misfire or idle rough.

In this case you'll see one or more of the following symptoms:

• Misfire trouble codes:
  • P0300: Random Cylinder Misfire.
  • P0301: Cylinder #1 Misfire.
  • P0302: Cylinder #2 Misfire.
  • P0303: Cylinder #3 Misfire.
  • P0304: Cylinder #4 Misfire.
• Blue smoke coming out of the tailpipe.
• Rough engine idle that disappears when you accelerate the engine.
• Bad fuel mileage.

The other type of compression problem is one that causes the engine to not start. To be a bit more specific the engine is going to crank but not start.

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

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

What makes testing the engine compression easy on the 2.4L engine is that removing the spark plugs is a breeze.

Once you have tested the compression of all four cylinders, then we'll move on to the next section which is interpreting the results of your compression test.

If you don't have a compression tester, you can borrow one from your local auto parts store or you can buy one Online. Check out my recommendations here: Which Compression Tester Should I Buy?

IMPORTANT: If the engine has been running for any length of time then let it cool down completely. Never remove the spark plugs from a hot engine or you run the risk of damaging the spark plug hole threads in the cylinder head.

OK, these are the test steps:

1. 1

   Disable the ignition system by disconnecting the ignition coil pack from its electrical connectors. This will prevent the ignition coil from sparking during the test.

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.
   
   Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper. Release the pressure on the gauge and repeat this step one more time.
   
   Repeat this test step 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

If you're reading this section then your compression test results show that one or more cylinders have a lower compression value than the others.

Up to a certain point this might be normal. But if the value varies too much (more than 15%), it'll cause a misfire or rough idle problem.

How do you figure this out? You can find out by using my online low compression calculator here: Online Low Engine Compression Calculator or by calculating 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 low compression value is usually caused by one of two things: either the cylinder's piston rings are worn out or its cylinder head valves are worn or damaged.

The cool thing is that we can find out without having to tear the engine apart by simply doing a wet compression test on the cylinder with the low compression value.

Now, if the compression value shoots up, after adding oil to the low compression cylinder, then you can conclude that the compression problem is due to worn out piston compression rings.

If the compression value does not increase, after adding oil to the low compression cylinder, then you can conclude that the problem is due to worn or damaged cylinder head valves.

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, or...
   
   2.) The needle will not move at all or stay at the same number you recorded earlier.
   
   What ever value your compression tester reads, write it down again.

5. 5

   Repeat steps 1 thru' 4 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 2.4L Chevy And Pontiac Tutorials

You can find a complete list of 2.4L Chevy and Pontiac tutorials here: GM 2.4L Index Of Articles.

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

• How To Test The MAP Sensor (2008-2012 2.4L Chevrolet Malibu).
• How To Test For A Blown Head Gasket (2.4L Cobalt, HHR, Malibu, G5, G6, Solstice).
• How To Do A Cylinder Balance Test (2.4L Cobalt, HHR, Malibu, G5, G6, Solstice).
• When Should I Replace The Spark Plugs (2.4L Cobalt, HHR, Malibu, G5, G6, Solstice).