Doing a compression test (and more importantly, interpreting the results of it) is not hard to do.
In this article, I'll walk you thru' the whole test in a step-by-step fashion and then I'll explain how to make sense of your test results.
Why do an engine compression test? Well, it may help you to find out if the engine is shot and if this is the reason why it won't start or the reason you have a hard to diagnose misfire condition.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar la Compresión del Motor (Ford 1.9L, 2.0L) (at: autotecnico-online.com).
Tools You'll Need:
- Compression Gauge Tester.
- A Helper
- Pen and Paper
The Engine Compression Test
To make sense of the results of the engine compression test, you need to know the number of the engine cylinder you're testing and so, I've provided the image (in the image viewer on the left) just for this purpose.
Although the compression test is not that hard to do (as you'll see shortly), I suggest you read all of the test steps first and familiarize yourself with them.
OK, this is what you'll need to do:
You'll get the most accurate test results if you perform the compression test with the engine in your Ford vehicle slightly warmed up.
There's a good chance that your Ford 1.9L or 2.0L vehicle does not start, in this case this tip does not apply to you. Continue to the next step.
If your Ford car does start... crank up the engine and let it run for about 20 minutes (and no more). If the engine has been running for an extended amount of time... it's important that you let it cool down for at least 45 minutes.
Disable the fuel system. You can do this by removing the fuel pump relay.
The reason you need to disable the fuel system is to keep the PCM from injecting fuel into the engine cylinders as you perform the compression test.
Disable the Ignition System. This can be done by simply disconnecting the ignition coil pack from its electrical connector.
It's important to disable the ignition system so that you won't have spark firing off at the spark plug wires (while you do the compression test).
Now, remove all of the spark plugs. As your taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plug’s ceramic insulator to break, and this will cause a misfire!
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.
Once the compression gauge is set up and hand tight in the spark plug hole... ask your helper to crank the engine.
Once the needle stops climbing on your compression gauge, have him or her stop cranking the engine.
Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper. Repeat steps 1 thru' 6 on the remaining three cylinders.
Let's turn the page and interpret your compression test results...