Interpreting Your Compression Test Results
If you're reading this section, more than likely the engine compression results you got from TEST 1 indicate that one or more cylinders have a lower compression value than the others.
Depending on the value of that low engine compression result you got, you may have nothing to worry about or it could be the source of the misfire that you're trying to troubleshoot.
It's not unusual for the cylinders to wear out unevenly, especially on high-mileage engines or engines that didn't get a lot of maintenance.
So in this section, I'm going to explain how you can find out if that low engine compression value is causing a problem or not.
OK, you can do this one of two ways: You can calculate this 15% difference with pen and paper or you can use my low compression calculator. You can find the low compression calculator here: Online Low Engine Compression Calculator.
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 a 2.2L Honda Accord I'm working on produced the following compression readings:
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
If you do have one or more cylinders with low or no engine compression, the next step is to find out what is causing that compression value.
Usually, one of two things will cause that low or no compression value you got in TEST 1.
Either the piston rings are severely worn/damaged or the cylinder head valves are worn/damaged in the dead cylinder.
We can easily find out without having to disassemble the engine with a wet engine compression test.
The wet engine compression test simply involves adding about 1-2 tablespoons of engine oil to the dead cylinder and then retesting it's compression.
If the compression value increases, then you can conclude that the piston rings, of the dead cylinder, are the ones behind its low compression value.
If the value does not increase, then you can correctly conclude that the low or no compression value is due to that cylinder having worn/damaged cylinder head valves.
OK, let's start:
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.
Install the compression tester onto the cylinder.
Do not use any type of tool to tightened the compression tester. Hand tight is fine.
When all is set up, have your helper crank the engine while you observe the gauge.
Once the needle on the gauge stops climbing, have your helper stop cranking the engine.
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.
Repeat steps 1-4 on any other cylinder with a low compression test result.
Let's examine your test results:
CASE 1: The compression value shot up. This tells you that that cylinder's piston compression rings are worn out and are behind the low compression test result you got in TEST 1.
CASE 2: The compression value stayed the same. This confirms that that cylinder's valves are behind the low to 0 PSI compression result you obtained in TEST 1.
More 2.2L Honda Accord, Odyssey And Prelude Tutorials
You can find a complete list of 2.2L Honda Accord and Odyssey tutorials in this index:
Here's a small sample of the tutorials you'll find in the index:
- How To Test The MAP Sensor (1994-1997 2.2L Accord, Odyssey, Prelude).
- How To Test The Head Gasket (1992-1997 2.2L Accord, Odyssey, Prelude).
- P0420 -What Does It Mean? (1995-1997 2.2L Honda Accord And Odyssey).
- How Often Should I Replace The Spark Plugs? (2.2L Honda Accord).
If this info really saved the day, buy me a beer!