How To Test Engine Compression (1991-1999 1.6L Nissan Sentra)

In this tutorial, I'll explain how to test the engine compression on Nissan vehicles with a 1.6L 4-cylinder engine. More importantly, I'll explain how to interpret the test results so that you can know whether you have a bad cylinder or not.

The engine compression test is easy and fast especially so because the 1.6L engine's spark plugs are very accessible and can be removed without much effort.

You can find this tutorial in Spanish here: Cómo Verificar La Compresión Del Motor (1.6L Nissan) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 1.6L Nissan Sentra: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999.

Important Tips And Suggestions

TIP 1: If your 1.6L Nissan's engine starts and runs, it's a good idea to let it warm up for about 15 minutes (before starting the compression test). I want to emphasize the key words: 'slightly warmed up engine' since it should not be hot.

Why warm up the engine? Because a slightly warmed up engine will improve the accuracy of your compression test results.

TIP 2: Take all necessary safety precautions as you work around a cranking engine. Use common sense and think safety all of the time.

TIP 3: The cylinder head, on your Nissan, is made of aluminum so you should never remove the spark plugs if the engine is hot (hot = normal operating temperature). Removing the spark plugs from a hot engine can/will damage the spark plug hole threads in the aluminum cylinder head.

Symptoms Of Low Or No Cylinder Compression

Generally, compression problems can be divided into two categories:

• Low compression in one or more cylinders causing a rough idle (misfire) when the engine is operating.
• Zero compression on all cylinders causing the engine to crank but not start.

Let's go into a more detailed look at these two types of problems:

Low compression on one or two cylinders in your engine 1.6L Nissan will cause the engine to misfire at idle. This misfire usually goes away when you accelerate the engine.

If your Nissan is OBD II diagnostic system equipped, you'll also see one or more of the following misfire trouble codes:

• P0300: Random Cylinder Misfire.
• P0301: Cylinder #1 Misfire.
• P0302: Cylinder #2 Misfire.
• P0303: Cylinder #3 Misfire.
• P0304: Cylinder #4 Misfire.

Unfortunately , even if your Nissan is equipped with OBD II, the computer doesn't always register a misfire fault code even when the engine is truly experiencing a cylinder failure.

Zero compression in two or more cylinders will cause your 1.6L Nissan to 'crank but not start'. Generally, this usually happens when the head gasket is blown or there's a timing belt/chain issue.

You'll also see one or more of the following symptoms:

• When you crank the engine to start it, it cranks very fast and this fast cranking speed is so noticeable that you know without a doubt that something's wrong.
• Each cylinder is getting spark. This let's you know that the engine's 'cranks but does not start' problem is not due to a fault in the ignition system.
• The fuel injectors are injecting fuel.
  • You can confirm this by checking the injector pulse with a Noid light.
  • You can confirm this by removing the spark plugs and verifying that they're soaked in gasoline.
• The most common causes of zero compression in all cylinders are:
  • Blown head gasket.
  • Broken timing belt.
  • Engine threw a rod.

Let's get testing.

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 some recommendations to you:

TEST 1: Dry Compression Test

You need to remove the spark plugs to perform compression test. I suggest you mark the spark plug wires before removing them so that you can install without complications/headaches when you complete the test.

CAUTION: Be careful and be alert at all times since you'll be working around a cranking engine.

NOTE: If your Nissan's engine is hot, wait for it to cool down before removing 4 spark plugs. Removing the spark plugs from a hot engine can damage the spark plug threads in the cylinder head.

Alright, these are the test steps:

1. 1

   Disable the ignition system by disconnecting the ignition distributor from its electrical connector. This will prevent the ignition coil from sparking during the test.

2. 2

   Remove the spark plugs from a slightly warmed up engine (if it starts and runs). Remember, the engine can not be hot!
   
   When removing the spark plugs, be careful not to drop any of them on the floor, or you run the risk of having the spark plugs porcelain insulator crack and then you'll have a misfire on your hands.
   
   If the engine does not start, don't worry about it being warmed up.

3. 3

   Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder. Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

4. 4

   Have your helper crank the engine till the needle on the compression gauge stops climbing.
   
   Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper. Release the pressure on the gauge and repeat this step one more time.
   
   Repeat this test step on the remaining 3 cylinders.

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

CASE 1: 0 PSI compression in 2 or all 4 cylinders. This test result indicates you have one of the following problems:

• Timing belt problem.
• Blown head gasket.
• Blown engine.

Any compression value below 100 PSI (even if it does not 0 PSI) means internal mechanical engine trouble.

CASE 2: Low compression in one or more cylinders. Up to a certain point, this could be normal (especially in high mileage engines).

But if the compression value is lower than 15% of the highest value you got, then that cylinder will cause a misfire.

We can easily find out, if the compression value is causing a problem or not, by doing some math. Go to: Interpreting Your Compression Test Results.

CASE 3: 0 PSI compression in one or more cylinders. The cylinder or cylinders with 0 PSI compression are considered 'dead' and are causing a misfire problem or a no-start problem.

The next step is to do a 'wet' compression test and find out if the problem is due to bad piston rings or bad cylinder head valves. Go to: TEST 2: Wet Compression Test.

Interpreting Your Compression Test Results

Depending on the age and mileage of your Nissan, there's a good chance that your compression test results show some of the cylinders have a lower compression value.

In most cases and if the difference in values is nothing big, you won't notice any engine performance problems.

When the difference is too big, you'll have a rough idle or a misfire condition 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 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 Compression Test.

TEST 2: Wet Compression Test

What usually causes a low compression test result is severe wear or damage to the cylinder head valves or the piston rings.

So, if your compression tester reported that one or more of the 4 cylinders has low compression, then your next step is repeat compression test after adding a little oil to the affected cylinder. This is known as a 'wet' compression test.

If the low cylinder compression is due to worn rings, the compression value of the affected cylinder will go up. If the problem is caused by worn cylinder head valves, the compression value will stay the same.

These are the test steps:

1. 1

   Add a tablespoon (or two) 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.

2. 2

   Once you've added the oil, install the compression gauge, and as before just hand tighten it.

3. 3

   Have your helper crank the engine till the needle stops climbing on the compression gauge.

4. 4

   You'll see one of two results:
   
   1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
   
   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.

5. 5

   Repeat steps 1 thru' 4 on any other cylinder with low or 0 PSI compression.

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

CASE 1: The compression value went up after adding motor oil and retesting. This tells you that the low compression problem is due to worn piston compression rings.

Here's why: The motor oil you just added helped the piston rings to create a tighter seal. With the piston rings now sealing the compression inside the cylinder, the compression value on your compression tester went up. This type of test result only happens when the problem is due to worn piston rings.

CASE 2: The compression value DID NOT go up after adding oil and retesting (in other words, it stayed the same). This result tells you that the low compression value registered in this cylinder (in the dry test) is due to worn/damaged cylinder head valves.

More 1.6L Nissan Sentra Tutorials

You can find a complete list of tutorials in this index: Nissan 1.6L Index Of Articles.

Here's a small sample of the 1.6L Nissan tutorials you'll find in the index:

• How To Test The TPS (1997-1999 1.6L Nissan Sentra).
• How To Test The Idle Switch (1997-1999 1.6L Nissan Sentra).
• How To Troubleshoot A No Start (1.6L Nissan).
• Mass Air Flow (MAF) Sensor Test Nissan Sentra 1.6L (1995-1999) (at: easyautodiagnostics.com).