How To Test Engine Compression (2.0L Ford)

Testing the cylinder compression on your 2.0L Ford Escort (Focus, Mercury Tracer) with a Single Over-Head Camshaft (SOHC) or Dual Over-Head Camshaft (DOHC) engine is pretty easy. Especially since the spark plugs are very accessible.

In this tutorial, I'll show you how to do and more importantly interpret a 'dry' and 'wet' engine compression test.

You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (2.0L Ford) (at: autotecnico-online.com).

Important Tips And Suggestions

TIP 1: You should warm up the engine for about 10 minutes (from a completely cold condition) if your 2.0L Ford starts and runs. The key words here are 'slightly warmed up engine' since the engine should not be hot.

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. Your safety is your responsibility, so use common sense and think safety all of the time.

TIP 3: Your 2.0L Ford engine's cylinder head is made of aluminum, so do not remove the spark plugs with a hot engine. 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

Engine compression problems fall into 2 basic categories:

• Low engine compression in one or two cylinders.
• No compression in all cylinders.

Low engine compression in one or more cylinders will cause a rough idle issue that can seem very hard to diagnose.

No compression in all cylinders results in a 'cranks but does not start' condition.

Here are some other specific symptoms you may see with low cylinder compression:

• Engine cranks but does not start (0 compression in all cylinders).
• Blue smoke coming out of the tailpipe.
• Rough idle (engine misfires).
• Bad gas mileage.
• Engine 'misses' at idle but 'miss' disappears as you accelerate.
• Check engine light is illuminated with a MAP sensor trouble code (even tho' the MAP sensor is good).

With this info under our belts, let's head down to the next subheading and 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'll need to remove the spark plugs for the engine compression test. To avoid damaging the spark plug wire, I recommend two very important things:

• Label the spark plug wires with the cylinder number they belong to.
• Use a spark plug wire puller tool to unplug the spark plug wire from the spark plug.

Why use a spark plug wire puller? Cause pulling on the wire boot by hand can cause the wire's metal terminal to pull off and stay stuck on the spark plug. The following tutorial offers you more info: How To Use A Spark Plug Wire Puller And Where To Buy One.

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

1. 1

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

2. 2

   Disable the fuel system by disconnecting the fuel injectors. Disabling the fuel system will prevent fuel from being injected into each cylinder when the test is performed.

3. 3

   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.

4. 4

   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.

5. 5

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

6. 6

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

7. 7

   Release the pressure on the gauge and repeat steps 5 and 6 one more time.

8. 8

   Check the compression of the remaining cylinders.

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

CASE 1: You got 0 PSI on all 4 cylinders. This test result lets you know that the engine has suffered one of the following conditions:

• A broken timing belt.
• A blown head gasket.
• A blown engine.

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

CASE 2: The compression values from each cylinder are slightly different from one another. Up to a certain point this could be normal.

If the compression value variation is within a certain range, then the engine won't suffer any performance problems. What will cause a problem is if the values vary too much. The cool thing is that we can find out if the variations in the values, you wrote down, indicate a problem (with that cylinder) or not. Go to: Interpreting The Results Of The Engine Compression Test.

Interpreting The Results Of The Engine Compression Test

A little variation between cylinder compression readings is normal and usually won't affect the way the engine runs.

But once one or more cylinders fall below 15% of the highest reading, that's when drivability problems like rough idle or misfires start to show up.

So how do you know if the numbers from your test cross that line? The easiest way is to plug them into my online calculator here: Online Low Engine Compression Calculator. Or, if you want to work it out yourself, here's the math:

• STEP 1: Take the highest compression reading and multiply it by 0.15 (15% in decimal form).
• STEP 2: Round the result to the nearest whole number (for example: 25.6 becomes 26).
• STEP 3: Subtract that number from your highest compression reading.
• ANSWER: The final number is the lowest compression value a cylinder can have before it's considered out of spec.

Here's an example to show you exactly how this works using real compression readings:

Cylinder	Pressure
#1	175 PSI
#2	170 PSI
#3	165 PSI
#4	120 PSI

The next step is to do the math:

• STEP 1: 175 x 0.15 = 26.25.
• STEP 2: 26.25 = 26.
• STEP 2: 175 - 26= 149.
• ANSWER: 149 PSI is the lowest possible compression value.

With cylinder #4 only showing 120 PSI, it’s clear this is the weak cylinder and the source of the misfire. The next step is figuring out why that compression is low. Head on over to: TEST 2: Wet Compression Test.

TEST 2: Wet Compression Test

The 'wet' engine compression test will help us find out if the low engine compression test result is due to bad piston rings or bad cylinder head valves.

This test simply involves adding a small amount of motor oil to the low compression cylinder and repeating the compression test.

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 (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

   Now, 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.
   
   Whatever value your compression tester reads, write it down again.

5. 5

   If you have another cylinder that needs to be tested, repeat steps 1 thru' 4 on it now.

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

CASE 1: The compression value shot up for the low compression cylinder. This test result confirms that the low compression value registered in this cylinder in the dry test is due to worn piston rings.

The reason the compression value shot up is due to the fact that the motor oil you just added helped the piston rings to create a tighter seal. This type of test result only happens when the problem is due to worn piston rings.

CASE 2: Your compression value DID NOT shoot up (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 2.0L Ford Diagnostic Tutorials

You can find a complete list of 2.0L Ford Escort (Focus) tutorials in these two indexes:

• Ford 2.0L Index Of Articles.
• Ford 1.9L, 2.0L Index Of Articles.

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

• How To Test The Fuel Injectors (2.0L Ford Escort).
• MAF Sensor TEST 2.0L Escort, Tracer (1997-2002).
• How To Test The Ford EGR Valve EGR Vacuum Solenoid, DPFE Sensor.
• How To Test The Crankshaft Position Sensor (Ford 1.9L, 2.0L) (at troubleshootmyvehicle.com).