How To Test Engine Compression (1997-2003 2.0L Ford Escort, Mercury Tracer)

Testing the engine compression on your 2.0L Ford Escort or Mercury Tracer isn't difficult, especially because the spark plugs are so accessible.

In this tutorial, I'm going to explain how to do the compression test and just as important, how to interpret its results.

Also how to do a wet compression test in case you get a low compression value from one or more cylinders so you can figure out if the issue is due to bad piston rings or worn out cylinder head valves.

All of the test steps are explained in a step-by-step manner so that you can quickly figure out whether the compression problem is causing a cylinder misfire or an engine no-start problem.

APPLIES TO: This tutorial applies to the following vehicles:

• 2.0L SOHC (P) Ford Escort: 1997, 1998, 1999, 2000, 2001, 2002.
• 2.0L DOHC (3) Ford Escort ZX-2: 1997, 1998, 1999, 2000, 2001, 2002.
• 2.0L SOHC Mercury Tracer: 1997, 1998, 1999.

Symptoms Of Low Or No Cylinder Compression

It's been my experience, having worked on cars for several decades, that engine compression problems usually cause one of two issues.

• Engine no-start problem: The engine cranks but doesn't start..
• Cylinder misfire, rough idle: In this scenario, low compression is causing the engine to misfire or have a rough idle. As soon as you step on the gas pedal, the issue disappears.

Now, if the engine starts and runs, but there's a cylinder compression problem, you're going to see one or more of the following engine performance issues.

• Blue smoke coming out of the tailpipe.
• Rough idle (engine misfires).
• Cylinder misfire setting one or more of the following codes:
  • P0300: Random Cylinder Misfire.
  • P0301: Cylinder #1 Misfire.
  • P0302: Cylinder #2 Misfire.
  • P0303: Cylinder #3 Misfire.
  • P0304: Cylinder #4 Misfire.
• 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

Alright, before we begin, I want to pass along some very important suggestions:

• Label the spark plug wires with the cylinder number they belong to.
• Use spark plug wire pullers to disconnect the wires from the spark plugs if your engine is a SOHC engine.
• Remove the spark plugs from a cold or completely cooled down engine.

If you just pull the spark plug wires off the spark plugs without a tool, you'll probably end up disconnecting the metal terminal inside the spark plug boot from the wire. The terminal can be crimped back on, but that's a hassle that you're probably better off not having to worry about.

If you don't have the spark plug wire puller, this is the one that I use and recommend: Performance Tool W80519 Adjustable Spark Plug Boot And Wire Remover (Amazon affiliate link).

About removing the spark plugs from a cold engine, this is important because if you remove the spark plugs from a hot engine, you risk stripping the spark plug hole threads in the cylinder head. Believe you me, this is a nightmare you don't want to have.

OK, time to get your hands dirty:

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 removing the fuel pump relay. 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.

CASE 3: All four cylinders show very similar compression values. This is exactly what you want to see.

When the compression numbers are close to one another, it tells you the engine's internals are in good shape. The cylinders are sealing properly, and there's no mechanical issue lurking inside. Bottom line: the engine is healthy and you can rule out compression as the cause of whatever problem you're chasing down.

Interpreting The Results Of The Engine Compression Test

On these engines, because of their age and mileage, up to a certain point, it's normal to have the compression values between cylinders vary a bit. Now when we run into engine performance problems is when the compression varies too much.

To be a bit more specific, we're talking about having the low compression values vary more than 15% of the highest compression value you got.

So if you got one that's much lower than that, that cylinder is going to misfire. Now, we can easily figure out if the low compression value you got is causing a problem by doing some simple math.

You can either do it with pen and paper, or you can use my online calculator here. Online Low Engine Compression Calculator. 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

Next, let's do a little math to find out the lowest acceptable reading:

• STEP 1: Multiply 175 by 0.15 = 26.25.
• STEP 2: Round 26.25 down to 26.
• STEP 3: Subtract 26 from 175 = 149.
• RESULT: 149 PSI is the lowest compression value this engine can be running with.

Since cylinder #4 is only showing 120 PSI, we're clearly looking at the weak cylinder and the reason for the misfire.

To know if your lowest compression number is still within limits, you'll be doing the same calculation —only this time you're using the highest reading from your own test instead of the sample numbers I have here.

The next thing we need to do is find out why the compression is low. Head over to: TEST 2: Wet Compression Test.

TEST 2: Wet Compression Test

For the most part, a low or 0 PSI compression problem in a cylinder is caused by one of two things:

• Worn out piston rings.
• Worn out or damaged cylinder head valves.

Thankfully, we don't have to tear the engine apart to find out which of the two is causing the compression issue in the cylinder.

We can do a wet compression test in which we add some engine oil to the low or 0 PSI compression cylinder and recheck its compression. We can expect one of two things:

• Compression is going to shoot up: This means that the low or 0 PSI compression issue is caused by the cylinder's piston rings.
• Compression doesn't move (stays the same): This means that the problem is in the cylinder's intake exhaust valves.

Alright, let's get to it.

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 go over what your test results mean:

CASE 1: The compression reading climbed higher (in the low or 0 PSI compression cylinder). This result confirms that the low reading you saw in the dry test is coming from worn out piston rings.

The reason the number climbed is because the motor oil you poured in is helping the piston rings seal tighter against the cylinder wall. You only see this type of jump when the issue is piston ring wear.

CASE 2: The compression reading DID NOT climb (it's staying the same). When this happens, the low or 0 PSI compression value you got earlier is caused by valves in the cylinder head that are worn or damaged and not sealing properly.

More 2.0L Ford Escort And Mercury Tracer Diagnostic Tutorials

You can find a complete list of 2.0L Ford Escort and Mercury Tracer tutorials in this index:

• 2.0L Ford Escort Index Of Articles.

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

• How To Test For A Blown Head Gasket (1997-2003 2.0L Ford Escort, Mercury Tracer).
• Common Causes Of Spark Plug Failure (1997-2003 2.0L Ford Escort, Mercury Tracer).
• How To Test The MAF Sensor (1997-2003 2.0L Ford Escort).
• How To Test The Throttle Position Sensor (1998-2003 2.0L Ford Escort ZX2).