How To Test Engine Compression (1999-2001 1.6L Mazda Protegé)

Engine compression problems are pretty common on small engines (such as the 1.6L Mazda engine) as they age and accumulate miles.

For the most part, engine compression problems usually lead to a rough idle condition and in extreme cases a 'cranks but does not start' condition.

This tutorial will help you do an engine compression test on your 1999-2001 1.6L Mazda Protegé in a step-by-step manner. More importantly, I'll show you how to interpret your test results to see if there's indeed a problem or not.

You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1999-2001 1.6L Mazda Protegé) (at: autotecnico-online.com).

Symptoms Of Low Or No Engine Compression

If your 1.6L Mazda Protegé idles rough or doesn't start, there's a good chance that the engine may have cylinder compression problems.

I'm gonna' go into details about both conditions so that you can see where your specific problem falls into:

Engine starts but runs with a misfire (rough idle):

1. Also known as an engine miss, rough idle condition.
   • Usually caused by very low compression in one cylinder or...
   • Uneven engine compression that varies more than 15% across all 4 cylinders.
2. Check Engine Light on with misfire codes:
   • P0300 Random Cylinder Misfire.
   • P0301 Cylinder #1 Misfire.
   • P0302 Cylinder #2 Misfire.
   • P0303 Cylinder #3 Misfire.
   • P0304 Cylinder #4 Misfire.
3. Bad gas mileage.
   • This is caused engine not producing its optimal power output since the air/fuel mixture isn't being combusted with adequate compression pressure.
4. Engine pollutes more.
   • If the air/fuel mixture isn't compressed within a certain range, it won't burn optimally and produce more unburned hydrocarbons escaping into the exhaust.

Your Mazda won't start:

This usually is caused by having 2 or all 4 cylinders with no compression. When this happens, you'll see:

1. The engine cranks very fast.
   • This fast cranking speed is very noticeable.
2. The Ignition System is sparking all 4 spark plugs.
   • This tells you that the no-start condition is not caused by a fault in the ignition system.
3. The fuel injectors spray fuel.
   • You can confirm this with a Noid Light test.
   • Also, you can confirm this, although indirectly, by removing the spark plugs and checking to see if they are fuel soaked (fuel fouled).
4. Fuel pump is working and providing pressure.
5. The most common causes of no compression on 2 or all 4 cylinders are:
   • Blown head gasket.
   • Broken timing belt.
   • Engine threw a rod.

OK, having covered the most common scenarios of low compression and no compression, let's get testing to see if this is the case on your 1999-2001 1.6L Mazda Protegé equipped vehicle.

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' Engine Compression Test

OK, to get this show on the road, we're gonna' check the compression of all 4 cylinders. If you don't have an engine compression tester, you can borrow one from your local auto parts store.

If you need help deciding where to buy one or which one to buy, take a look at my recommendations: Which Compression Tester Should I Buy?

IMPORTANT: Do not remove the spark plugs from a hot engine, or you run the risk of damaging the spark plug threads on the cylinder head. If the engine has been running for any length of time, let it cool down completely. Also, you'll be working around a cranking engine, so you have to be careful and stay alert at all times. Think safety all of the time!

Alright, these are the test steps:

1. 1

   Disconnect all of the fuel injectors. This will prevent fuel from being injected into the cylinders as you crank the engine.

2. 2

   Remove all the 2 ignition coils (along with the 2 spark plug wires).

3. 3

   Remove all four spark plugs.
   
   As you're taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plugs ceramic insulator to break, and this will cause a misfire!

4. 4

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

5. 5

   When the tester is set up, ask your helper to crank the engine. Your job is to keep your eye on the compression tester's gauge.

6. 6

   Once the needle on the gauge stops climbing, have your helper stop cranking the engine.

7. 7

   Write down the compression value on a piece of paper. Include the number of the cylinder this reading belongs to.

8. 8

   Now repeat steps 4 thru' 7 on the other 3 cylinders.

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

CASE 1: Low or no compression in 2 or all 4 cylinders. This test result indicates a serious internal problem.

The most common issues would be:

• Blown head gasket.
  • To further test this, I recommend the following tutorial: How To Test For A Blown Head Gasket (1.6L Mazda Protegé).
• Broken timing belt.
• Engine threw a rod.

CASE 2: Low or no compression in one cylinder. Getting a no or low compression test result means you've found the cause of the engine's rough idle (misfire).

If you got a low compression reading, the next step is to find out if this reading is varying by more than 15% than the other cylinders (because if it is varying by more than 15%, then this cylinder is considered 'dead'). Go to: Interpreting Your Compression Test Results:

Interpreting Your Compression Test Results

It's not unusual to see the compression values vary a bit, especially in high mileage engines.

If the low compression value is within a certain range, it won't cause any problems and you probably won't notice anything.

But if the compression value varies by more than 15% of the highest one, then you've got a cylinder that will cause a misfire.

Alright, finding out if the low compression value is causing a problem can be done 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' Engine Compression Test

What usually causes a low or no engine compression test result is that that specific cylinder has bad cylinder head valves or worn piston rings.

The cool thing is that we can find out without having to tear down the engine by doing a 'Wet' compression test.

Doing a 'Wet' compression test simply involves adding about two tablespoons of oil to the confirmed 'dead' engine cylinder.

The engine oil that you're gonna' add to the cylinder will help determine if the low compression reading 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.

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.
   
   Hand tighten the compression tester only, do not use any type of tool to tightened it.

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 out and thus the problem is in the bottom end (block) of the engine in your 1999-2001 1.6L Mazda Protegé.

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