How To Test Engine Compression (1989-1997 1.6L Toyota Corolla)

If you've been wondering what's involved in testing and interpreting an engine compression test on your 1.6L Toyota Corolla (1.6L Geo Prizm), then this is the tutorial you need.

Testing the engine compression on your 4 cylinder Corolla (Prizm) is a pretty easy affair due to the fact that the spark plugs are easily accessible (since they have to be removed for the test).

In this tutorial, I'll show you how to troubleshoot a low engine compression problem causing a rough idle or a no-start condition.

APPLIES TO: This tutorial applies to the following vehicles:

• 1.6L (4A-FE) Toyota Corolla: 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.
• 1.6L (4A-GE) Toyota Corolla: 1989, 1990, 1991.
• 1.6L Geo Prizm: 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997.

Engine No-Start Diagnostics:

• How To Troubleshoot An Engine No-Start Problem (1989-1992 1.6L Toyota Corolla).
• How To Troubleshoot An Engine No-Start Problem (1993-1997 1.6L Toyota Corolla).

Important Tips And Suggestions

TIP 1: If the engine in your 1.6L equipped Corolla (Prizm) starts and runs you should test the cylinders' compression with a slightly warmed up engine. I want to stress the words: slightly warmed up because the engine SHOULD NOT be hot.

Testing the cylinders' compression with a slightly warmed up engine will ensure the accuracy of your engine compression test results.

TIP 2: You'll be working around a cranking engine as you perform the engine compression test so take all necessary safety precautions. Please use common sense and think safety all of the time.

TIP 3: All of the spark plugs need to be removed from the engine for the compression test and this must never be done with a hot engine.

Why? The spark plug threads in the cylinder head can easily get damaged (as in getting stripped) and this is a nightmare you do not want to experience.

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:

TEST 1: Dry Compression Test

The compression tests, in this tutorial, are divided into two parts. One is a 'dry' compression test and the other is a 'wet' compression test.

The difference being that the 'wet' compression test is done after finding one (or more/all) cylinders with no or low engine compression.

NOTE: Before you remove the spark plugs, mark each spark plug wire's location. This will make it easier to put them back in their proper places a whole lot faster.

OK, to get started this is what you'll need to do:

1. 1

   Disable the fuel system by removing the fuel pump fuse. Disabling the fuel system will prevent fuel from being injected into each cylinder when the Test is performed.

2. 2

   Disable the ignition system by disconnecting the distributor from its electrical connector(s).

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.

5. 5

   Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper.

6. 6

   Release the pressure on the gauge and test the cylinder's compression one more time.

7. 7

   Test the compression on the remaining 3 cylinders.

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

CASE 1: 0 PSI on all 4 cylinders. This is bad and it tells your that 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, these low compression values will not cause a problem.

But if they are too low, then you'll have a misfire problem or a rough idle problem. To find out, go to: Interpreting Your Compression Test Results.

Interpreting Your Compression Test Results

On high mileage engines, it's not unusual to find that the cylinders have varying compression values.

If the variation in these values is low enough, you're not gonna notice any engine performance problems.

Thankfully, finding out if a low compression value is causing a misfire or a rough idle problem isn't hard.

The key to finding out if the lower compression value is causing a problem, is 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 Engine Compression Test.

TEST 2: Wet Compression Test

If in TEST 1 you found that one (or more) cylinders had low (or no) compression, the next step is to find out if that compression test result is due to worn cylinder head valves or worn piston rings.

We can do this by simply adding about 1 or 2 tablespoons of motor oil to the affected cylinders and retest them. The compression result that we're looking for (in the re-test after the oil has been added) is if the compression value goes up or not.

If the compression value goes up, then we can conclude that the low compression (in that cylinder) is due to worn piston rings. If the compression value does not go up, then we can conclude the problem is in the cylinder head valves.

At the bottom, I'll show you how to interpret your test results.

OK, this is what you'll need to do:

1. 1

   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.

2. 2

   Once you've added the oil, install the compression gauge. 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 that needs to be tested.

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

CASE 1: Your compression tester registered a higher value. This compression test result confirms that the low compression value registered in this cylinder in the dry test is due to worn piston rings.

CASE 2: Your compression tester DID NOT register a higher value (than the previous recorded value). 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.