How To Test Engine Compression (2000-2006 1.8L Nissan Sentra)

Interpreting Your Compression Test Results

On high mileage vehicles, it is not uncommon for compression readings to differ between cylinders.

Up to a point, this difference in compression values does not cause engine performance issues.

But if the values vary beyond a certain range, then you'll definitely have a misfire or rough idle problem on your hands.

To find out if the lower compression value is causing a problem, you need to find out if it's lower than 15% of the highest compression value you got.

You can do this (figuring out the 15%) in 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 (at: easyautodiagnostics.com).

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 I got the following compression readings:

Cylinder	Pressure
#1	165 PSI
#2	95 PSI
#3	155 PSI
#4	175 PSI

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 reading you got from your engine compression test is in a good range, you need to do the same calculation. Of course, you must use the highest compression value you got, not the one in the example.

Once you've found the 'dead' cylinder, the next step is to figure out what's causing the low compression reading. For this step go to: TEST 2: 'Wet' Engine Compression Test.

TEST 2: 'Wet' Engine Compression Test

The next step, after determining and/or confirming that you do indeed have a 'dead' cylinder on your hands, is a 'wet' compression test.

All this means is adding about two tablespoons of oil to the confirmed 'dead' engine cylinder.

The engine oil you fill the cylinder with will help determine if the low compression reading you got in the 'dry' compression tests are caused by worn piston rings or worn cylinder head valves.

Depending on whether the compression pressure increases (on your compression tester) or not, you'll be able to say the problem is with the piston rings or with the cylinder head valves.

OK, this is what you need to do:

1. 1

   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.

2. 2

   Install the compression tester onto the cylinder.
   
   Do not use any type of tool to tightened the compression tester. Hand tight is fine.

3. 3

   When all is set up, have your helper crank the engine.

4. 4

   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.

Let's take a look at what your test results mean:

CASE 1: The compression value shot up. This tells you that the piston compression rings are worn and therefore the problem is at the bottom end (block) of the engine in your 1.8L Nissan Sentra.

CASE 2: The compression value stayed the same. This confirms that the affected cylinder's low compression issue is due to worn or damaged cylinder head valves.

More 1.8L Nissan Tutorials

You can find all of the 1.8L Nissan equipped vehicle articles here:

• Nissan 1.8L Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Ignition COP Coils (Nissan 1.8L).
• Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999) (at: easyautodiagnostics.com).
• How To Test The 2000-2002 Nissan Sentra 1.8L MAF Sensor (at: easyautodiagnostics.com).