In this tutorial I'm gonna' explain how to do the 2 different types of compression test on the Ford Ranger's 3.0L V6 engine.
The first test is a dry compression test. This test is designed to find the ‘dead’ cylinder or cylinders.
After the ‘dead’ cylinders have been identified, the next step is to do a wet compression test.
This wet compression test will now pinpoint the source of the problem of the ‘dead’ cylinder's low (or zero) compression test result.
NOTE: This tutorial applies to the 1995-2008 3.0L V6 Ford Ranger and 1995-2006 3.0L V6 Mazda B3000.
Contents of this tutorial at a glance:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1995-2008 3.0L Ford Ranger) (at: autotecnico-online.com).
Symptoms Of Engine Compression Problems
What usually causes a cylinder to suffer low (or zero) compression is that its piston rings or cylinder head valves have severely worn out or are damaged.
Depending on how many of the 6 cylinders are affected by low (or zero) compression, the engine on your 3.0L V6 Ford Ranger (or Mazda B3000) will either not start or start but run with a misfire (or very rough idle).
To be a bit more specific, if you have very low (or zero) compression on the majority of the engine cylinders, the engine is not going to start.
Now if you have one or maybe two cylinders with low compression, the engine is going to run but it's going to run with a misfire.
TEST 1: Dry Compression Test
OK, our first test we are going to remove all of the spark plugs and test the compression of all six cylinders.
You may be wondering if it's necessary to test all 6, and the answer is no, you don't have to test all of them.
But, I suggest that you do test all 6 because this will help you to obtain the highest compression reading that you'll need to interpret your compression test results in the next section.
NOTE: It's very important that you remove the spark plugs from a completely cold engine. If you remove the spark plugs from a hot engine, you risk damaging the threads in the spark plug holes (in the cylinder head).
OK, these are the test steps:
Disconnect the spark plug wires from the spark plugs.
NOTE: Label each spark plug wire with the number of the cylinder it belongs to. This will prevent losing the firing order of the spark plug wires.
Remove the spark plugs from a cold engine.
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 plug's porcelain insulator crack (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: You got 0 PSI compression on all cylinders. This test result is usually the result of mechanical damage in the engine.
The most likely cause are:
- Timing chain problem.
- Blown head gasket.
- Blown engine.
Any compression value below 100 PSI (even if it doesn't go down to 0 PSI) means internal mechanical engine trouble.
CASE 2: You got uneven compression values between engine cylinders. The next step is to find out if any of those values is too low and causing a problem.
To find out, go to: Interpreting The Compression Test Results.