TEST 2: Wet Compression Test
The very last step, if you have one or more cylinders that have very low compression values, is to do a wet compression test on those specific cylinders.
This type of test will help you find out if the low compression value is due to worn valves in the cylinder head or worn rings on the pistons.
This involves adding a spoonful of engine oil to the affected cylinder and testing the compression again.
OK, this is what you'll need to do:
Add a 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.
Once you've added the oil, install the compression gauge, and as before just hand tighten it.
Now, have your helper crank the engine till the needle stops climbing on the compression gauge.
As before, your job is to keep an eye on the gauge, and 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.
If you have another cylinder that needs to be tested, repeat steps 1 thru' 4 on it now.
Interpreting The Results Of The Engine Compression Test
The Wet compression test will only give you one of two results (on the specific cylinder you added engine oil and re-tested):
CASE 1: The needle on the gauge registered a higher value This tells you that the lack of compression (or low compression) recorded earlier is due to BAD or severely worn piston rings.
CASE 2: The needle DID NOT move beyond the previous recorded value, This result tells you that the problem is due to worn intake or exhaust valves in the cylinder head.
Why An Engine Compression Test?
One of the things that can cause a misfire condition (also known as a miss or dead cylinder), is an engine cylinder or engine cylinders that produce less than normal compression.
When this happens, not matter what gets replaced (like spark plugs, spark plug wires, fuel injectors), nothing solves the miss. This is when the compression test comes in to save the day.
Over the years, I have solved many unsolvable misfire codes, rough idle, lack of power issues by doing a simple engine compression test and if you're faced with something similar then I highly recommend doing an engine compression test.
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 in any auto parts store in any neighborhood, in any city but you'll be paying at least twice as much. Go to the above compression tester links, browse and compare, you'll see a big price difference!
Related Test Articles
To see all of the 1.8L and 2.4L Mitsubishi (Dodge, Chrysler) specific articles here at troubleshootmyvehicle.com, go to: Mitsubishi 2.4L Index Of Articles.
Here's a sample of the articles you'll find in the Index of Articles:
- Crank Sensor Test and Ignition Coil Tests.
- MAF Sensor Test.
- Throttle Position Sensor Test.
- How To Test The Alternator.
- How To Bench Test The Starter Motor.
If this info really saved the day, buy me a beer!