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:
You can find this tutorial in Spanish here: Cómo Verificar La Compresión Del Motor (3.0L Ford Escape) (at: autotecnico-online.com).
Important Tips And Suggestions
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. 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.
Symptoms Of Low Or No Cylinder Compression
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.
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:
1) Which one to buy: The engine compression tester that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it does not come with a case to store it in.
2) Where to buy: You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!
TEST 1: Dry Compression Test
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's 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.
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: 0 PSI on all cylinders. This means that the engine has a serious internal mechanical problem caused by one of the following:
- 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: Low compression in one or more cylinders. Up to a certain point this variation in the compression values could be 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. To find out go to: Interpreting Your Compression Test Results.