In this tutorial, I'll explain how to perform the two different types of compression tests on the Ford Ranger 3.0L V6 engine.
The first test is a dry compression test, which will identify the 'dead' cylinder or cylinders.
After the 'dead' cylinders have been identified, the next step is to perform a wet compression test.
This wet compression test helps determine the source of the low (or zero) cylinder compression test result you obtained from the dry compression test.
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).
APPLIES TO: This tutorial applies to the following vehicles:
- 3.0L Ford Ranger: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008.
- 3.0L Mazda B2300: 1994, 1996, 1997, 1998, 1999, 2001, 2002, 2003, 2004, 2005, 2006.
Symptoms Of Engine Compression Problems
What usually causes a cylinder to suffer from low (or no) compression is that its piston rings or cylinder head valves are badly worn or damaged.
Depending on how many of the 6 cylinders are affected by low (or zero) compression, your 3.0L V6 Ford Ranger (or Mazda B3000) engine will either not start or start, but will misfire (or very rough idle).
More specifically, if you have very low (or zero) compression on most engine cylinders, the engine will not start.
Now if you have one or maybe two low compression cylinders, the engine will run, but it will run with a misfire.
Which Compression Tester Should I Buy?
There are many engine compression testers to choose from and many places to buy them. I give you two recommendations:
1) Which to buy: The engine compression tester I've always used is this Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that it doesn't come with a storage case.
2) Where to buy: You can buy an engine compression tester at any auto parts store in any neighborhood or city, but you'll pay at least twice as much. Go to the above compression tester links, browse and compare, you'll see a huge price difference!
TEST 1: Dry Compression Test
OK, for our first test, we'll remove all the spark plugs and test the compression on all six cylinders.
You may be wondering if it's necessary to test all six and the answer is no, you don't have to test all of them.
But I suggest you test all six as this will help you get the highest compression reading you 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, there's a risk of damaging the threads in the spark plug holes (in the cylinder head).
OK, these are the test steps:
- 1
Disconnect the spark plug wires from the spark plugs.
NOTE: Label each spark plug wire with the cylinder number to which it belongs. This will prevent losing the firing order of the spark plug wires. - 2
Remove the spark plugs from the engine.
When removing the spark plugs, be careful not to drop any of them on the floor, otherwise you risk cracking the spark plug's porcelain insulator (then you'll have a misfire on your hands). - 3
Install the engine compression gauge into the spark plug hole for engine cylinder number 1.
NOTE: Only tighten the compression gauge by hand! Don't use any tool to tighten it. - 4
Have your helper crank the engine until the needle on the compression gauge stops rising.
- 5
Write down the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
- 6
Repeat test steps 3 through 5 on the remaining cylinders.
Let's see 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 causes are:
- Timing chain problem.
- Blown cylinder head gaskets.
- Engine threw a rod.
Any compression reading below 100 PSI (even if it doesn't go down to 0 PSI) indicates internal mechanical engine problems.
CASE 2: You got uneven compression readings between engine cylinders. The next step is to find out if any of these values are too low and causing a problem.
To find out, go to: Interpreting Compression Test Results.
