The engine compression test can tell you the condition of the engine and the cool thing is that doing a compression test on the 1.5L Toyota Tercel engine is easy!
What makes it so easy is that the spark plug (which have to be removed) are very accesible.
In this tutorial I'll show you how to do the test and more importantly, how to interpret your test results.
Contents of this tutorial at a quick glance:
- Important Tips and Suggestions.
- TEST 1: Dry Compression Test.
- TEST 2: Wet Compression Test.
- Which Compression Tester Should I Buy?
Important Tips and Suggestions
TIP 1: Be alert and careful since you'll be working around a cranking engine. Use common sense and think safety all of the time.
TIP 2: All of the spark plugs need to be removed from the engine for the compression test and this must never be done with a hot engine.
Why? The spark plug threads in the cylinder head can easily get damaged (as in getting stripped) and this is a nightmare you do not want to experience.
TEST 1: Dry Compression Test
To get this show on the road, we're gonna' remove all of the spark plugs and check the compression of all 4 cylinders.
Once you've gotten all four compression readings, we're gonna' do some math to find out if any of those compression readings are causing a problem.
OK, to get started this is what you'll need to do:
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.
Disable the fuel system by removing the fuel pump fuse. Disabling the fuel system will prevent fuel from being injected into each cylinder when the test is performed.
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.
Write the value down and repeat this test step on the remaining 3 cylinders.
Let's take a look at what your test results mean:
CASE 1: If Your Car Does Not Start and the results of the engine compression test are 0 PSI on all 4 cylinders then you have one of the following conditions:
- Timing belt 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 Your Car 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 1.5L Toyota Tercel produced the following compression test results:
- Cylinder #1 175 PSI.
- Cylinder #2 170 PSI.
- Cylinder #3 165 PSI .
- Cylinder #4 130 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!!