In this tutorial, I'll explain how to test the engine compression on the Ford Escape (Mazda Tribute) with a 3.0L 6-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.
As you're probably already aware, it can be quite a challenge to do a compression test on the Escape's V6 engine since the intake manifold plenum has to be removed. Having removed it a few times before myself, I have a few suggestions to make the job a little less complicated.
Contents of this tutorial at a quick glance:
- Important Tips and Suggestions.
- Symptoms of Low or No Cylinder Compression.
- TEST 1: Dry Compression Test.
- TEST 2: Wet Compression Test.
- The Intake Manifold Plenum Has to be Removed.
- Which Compression Tester Should I Buy?
You can find this tutorial in Spanish here: Cómo Verificar la Compresión del Motor (3.0L Ford Escape) (at: autotecnico-online.com).
TIP 1: You'll need to remove the intake manifold's plastic plenum to access the spark plugs in bank 1 of the engine. Bank 1 is the cylinder head that houses spark plugs for cylinders #1, #2, and #3. Although I don't include any remove and replace instructions, I recommend that you take a look at the following section: The Intake Manifold Plenum Has to be Removed.
TIP 2: You'll be working around a cranking engine, when doing a compression test. This means you have to be alert and take all necessary safety precautions. Your safety is your responsibility... so use common sense and think safety all of the time.
TIP 3: Your Ford Escape (Mazda Tribute) comes equipped with cylinder heads that are made of aluminum. This means that you need to wait till the engine is completely cooled down before you remove the spark plugs. Removing the spark plugs from a hot engine can/will damage the spark plug hole threads in the aluminum cylinder heads.
Generally, compression problems can be divided into two categories:
- Low engine compression in one or several cylinders causing a misfire condition and misfire trouble code.
- Zero compression on all cylinders causing your Ford Escape's 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 3.0L Ford Escape will cause the engine to misfire at idle. This misfire usually goes away when you accelerate the engine.
If your Ford 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.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
Unfortunately , even if your Ford 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 3.0L Ford Escape 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 chain.
- Engine threw a rod.
Let's get testing...
As mentioned earlier, the intake manifold's plastic plenum has to be removed to test the compression on cylinders 1, 2, and 3. If you haven't already, take a look at the suggestions here: The Intake Manifold Plenum Has to be Removed.
Alright, these are the test steps:
Remove the intake manifold plastic plenum and remove all 6 ignition coils.
Remove the spark plugs. 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.
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.
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 cylinders.
Let's take a look at what your test results mean:
CASE 1: If the engine does not start and the results of the engine compression test are 0 PSI on all cylinders then you have one of the following conditions:
- Timing chain 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: If the engine does start, the very first thing you'll notice is that the compression values you wrote down for each cylinder are slightly different from one another. This is normal.
What is NOT normal 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.
The rule of thumb is that they can not vary more than 15% from each other and if they do... you're gonna' have a genuine misfire condition on your hands or possibly a No Start Condition (if more than one cylinder is affected).
How do you figure this out?... This is how you do it:
- Grab a calculator and multiply the highest compression reading that you recorded by .15. So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X .15 gives you 26 (25.5 rounded off).
- Now, the next step is to subtract 26 from 170... which gives us 144 PSI.
- So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this.. and that engine cylinder will misfire.
To make better sense of the above calculation... let's say that my 3.0L Ford Escape produced the following compression test results:
- Cylinder #1 175 PSI.
- Cylinder #2 165 PSI.
- Cylinder #3 160 PSI.
- Cylinder #4 110 PSI.
- Cylinder #5 170 PSI.
- Cylinder #6 160 PSI.
The next step is to do the math: 175 x .15= 26, 175-26= 149. So, now I know that cylinder #4 is the one causing the misfire!!