Interpreting The Results Of The Engine Compression Test
There's a good chance that the compression values you got in TEST 1 vary between them. Within a certain range, the variation in the compression values doesn't cause any engine performance problems.
What could cause a problem is if the cylinder compression values vary too much. The cool thing is that we can find out if the variations in the values, you wrote down, indicate a problem (with that cylinder) or not.
The rule of thumb is that they can not vary more than 15% from each other and if they do, you're gonna' have a genuine misfire condition on your hands or possibly a no-start condition (if more than one cylinder is affected).
How do you figure this out? You can find out by using my online low compression calculator here: Online Low Engine Compression Calculator or manually this way:
- 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.
To make better sense of the above calculation, let's say that I got the following compression test results:
| Cylinder | Pressure |
|---|---|
| #1 | 175 PSI |
| #2 | 170 PSI |
| #3 | 165 PSI |
| #4 | 120 PSI |
The next step is to do the math:
- STEP 1: 175 x 0.15 = 26.25.
- STEP 2: 26.25 = 26.
- STEP 2: 175 - 26= 149.
- ANSWER: 149 PSI is the lowest possible compression value.
Since cylinder #4 is producing 120 PSI, I can conclude that it's the one causing the misfire. The next step is to find out what's causing the low compression value. Go to: TEST 2: Wet Compression Test.
TEST 2: Wet Compression Test
Once you've found out which is the cylinder (or cylinders) with low compression, the next step is to add about 1 to 2 teaspoons of oil to the cylinder and repeat the compression test.
Now, if the reason, why the compression was low, is due to a problem with worn out piston rings, the oil will make the worn out rings seal and the compression value (as recorded by your compression tester) will go up.
If the compression value doesn't go up, then now you know that the problem is in the cylinder head valves and not in the piston rings.
OK, this is what you need to do:
- 1
Add the engine oil to the cylinder with low to no compression.
Remember, you should add about 1 to 2 teaspoons of oil. - 2
Install the compression tester onto the cylinder.
Hand tight is fine. Don't use any type of tool to tighten it. - 3
When all is set up, have your helper crank the engine.
- 4
You'll see one of two results:
1.) Your compression tester will either record a higher reading than the one recorded before.
2.) The compression tester will record the same reading as before.
Let's see what your compression test result means:
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.
CASE 2: The compression Value stayed the same. This confirms that the problem is in the cylinder head valves.
Related Articles
You can find a complete list of Suzuki test articles here: Suzuki Index Of Articles.
Here's a list of articles you'll find there:
- How To Test The Ignition Coils Suzuki: Swift, Vitara - Chevy: Metro, Tracker.
- How To Troubleshoot A Misfire (Suzuki 1.3L, 1.6L, 1.8L, 2.0L, 2.3L).
- How To Test The 2.5L COP Coils.
If this info saved the day, buy me a beer!
