The ‘Wet’ Engine Compression Test
The next step, after finding out that you do have one or more cylinders with low compression, is to add about 2 tablespoons of oil to them and then retest their compression once more.
The oil that you're gonna' add to the cylinder will help determine if the low cylinder pressure or pressures you recorded in the ‘Dry’ compression test are caused by worn piston rings or worn cylinder head valves.
Depending on whether the compression pressure rises (on your compression tester) or not, you'll be able to say that the problem lies in the piston's rings or in the cylinder head valves.
This test, in which you add engine oil to the cylinders, is known as a ‘Wet’ compression test.
OK, this is what you need to do:
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.
You'll get one of two results, either the compression value will go up (from the one you recorded before) or it will stay the same.
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 (block) of the engine in your 3.0L, 3.3L, or 3.5L Nissan.
CASE 2: The compression value stayed the same. This confirms that the problem is in the cylinder head valves.
Why An Engine Compression Test?
An engine compression test is one of the most important tests to perform when trying to solve a hard to diagnose misfire condition / rough idle condition. If only one cylinder has below average compression (compared to the other 5 cylinders), that cylinder will not contribute to engine power and you're gonna' feel it.
Also, no matter what you replace, the misfire condition or misfire codes (P0300, P0301, P0302, P303, P0304, P0305, P0306) will not go away! Unfortunately, the engine compression test is one of the most overlooked misfire troubleshooting tests. Now, testing the compression of each cylinder is usually done after verifying that each cylinder is getting spark (this can be easily accomplished by using a spark tester).
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 just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!
Related Test Articles
You can find more ‘How To Test’ articles for your 3.0L, 3.3L, 3.5L equipped Nissan car, pick up or mini-van at: 3.0L, 3.3L, 3.5L Nissan Index Of Articles.
Here's a small sample of the tutorials you'll find in the index:
- How To Test The Starter Motor (Nissan 3.0L, 3.3L).
- Mass Air Flow (MAF) Sensor Test 3.0L Nissan Maxima (1995-1999) (at: easyautodiagnostics.com).
- Power Transistor Test & Ignition Coil Test 3.3L Nissan (1996-2004) (at: easyautodiagnostics.com).
- How To Test The Throttle Position Sensor (1996-1999 3.0L Maxima) (at: easyautodiagnostics.com).
If this info saved the day, buy me a beer!