Testing the engine compression on the 1.6L DOHC engine in your Ford Fiesta is a breeze, since the spark plugs are very accessible.
In this tutorial, I'll explain how to perform the test in a step by step manner and I'll also tell you how to interpret your test results.
Whether a compression problem is causing a misfire or an engine no-start problem, I'll help you figure it out.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 1.6L Ford Fiesta: 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018.
Symptoms Of Low Or No Engine Cylinder Compression
As mentioned at the beginning of this tutorial, engine compression problems usually cause one of two problems.
The engine compression problem will cause a misfire problem. This means that the engine will start and run but it's going to run with one or more dead cylinders.
In the worst-case scenario, an engine compression problem will keep the engine from starting. It'll crank but not start.
When an engine compression problem is allowing the engine to start, you're going to see one or more of the following symptoms:
- Bad gas mileage.
- Blue smoke coming out of the tailpipe.
- A heavier exhaust smell coming out of its tailpipe.
- Engine is not as peppy as it was once.
- Rough idle that goes away as soon as you accelerate the engine.
- The check engine light is illuminated on the instrument panel.
- Misfire trouble codes illuminating the check engine light. You many see one or more of the following:
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
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 some recommendations to you:
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TEST 1: Finding The Dead Cylinders
I'm gonna recommend that you test the compression of all four cylinders. This way, we can get a complete picture of the engine's internal health.
Once you've got all four compression readings, I'll help you interpret them in the 'CASES' section below the test instructions.
If you don't have a compression tester, you can borrow one or buy one from your local auto part store. If you'd like to save a few bucks, check out my recommendations here: Which Compression Tester Should I Buy?
IMPORTANT: If the engine has been running for any length of time, let it cool down completely before removing the spark plugs.
OK, these are the test steps:
- 1
Disable the ignition system by disconnecting the ignition coil pack from its electrical connector.
This will prevent the ignition coil from sparking during the test. - 2
Remove the spark plugs. Remember, the engine can not be hot!
When removing the spark plugs, be careful not to drop any on the floor, or you run the risk of having the spark plug's porcelain insulator crack and then you'll have a misfire on your hands. - 3
Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder.
NOTE: Hand tighten the compression gauge only! Do not use any type of tool to get it tight. - 4
Have your helper crank the engine till the needle on the compression gauge stops climbing.
- 5
Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
- 6
Release the pressure on the gauge and repeat step 4 and 5 one more time.
- 7
Repeat test steps 3 - 5 on the remaining cylinders.
Let's examine your test results:
CASE 1: One or more cylinders had a much lower compression value than the others. Up to a certain range, this could be normal.
To further interpret these test results go to: Interpreting The Compression Test Results.
CASE 2: All four cylinders had almost no compression or 0 PSI compression. This low or zero compression on all cylinders will cause the engine to not start.
Having a compression value close to 0 PSI or 0 PSI is usually due one of the following problems:
- A busted timing belt.
- Blown head gasket.
- The engine threw a rod.
CASE 3: The compression value of all four cylinders was similar and above 120 PSI. This test result lets you know that an engine compression problem is not behind the misfire condition and/or engine no-start problem you're troubleshooting.
Interpreting The Compression Test Results
It's pretty common to see the compression values vary a bit, especially on high mileage engines. Up to a certain point, these variations don't affect engine performance.
It's when one or more values a too low that you're gonna have an engine performance issue causing a rough idle/misfire problem and lighting the check engine light on your Ford Fiesta.
Finding out if the low compression values you got from your test are causing a problem is not difficult. In this section, I'll explain how to do just that.
The rule of thumb is that the lowest compression value can not vary more than 15% of the highest value (that you wrote down in TEST 1). If any value is lower by more than 15%, then that engine cylinder is going to misfire. This misfire will cause your Ford Fiesta's engine to idle rough.
How do you figure this out? You can find out by using my online low compression calculator here: Online Low Engine Compression Calculator (at: easyautodiagnostics.com) or by calculating this 15% difference manually.
To understand how to figure out this 15% thing manually, I'll use the following compression test results:
- Cylinder #1 175 PSI.
- Cylinder #2 165 PSI.
- Cylinder #3 160 PSI.
- Cylinder #4 120 PSI.
The next step is to do the following math:
- Multiply .15 (15%) by the highest value: 175 x 0.15. This gives us 26.25, but we'll round it out to 26.
- Next, we subtract 26 from 175: 175 - 26 = 144.
- So now we know that the lowest possible compression value is: 144 PSI.
This means that cylinder #4, which has a compression value of 120 PSI, is the one causing the misfire because it's below the 144 PSI minimum.
Once we've found the 'dead' cylinder, the next step is to find out what's causing the low compression value. For this step, go to: TEST 2: Wet Engine Compression Test.
TEST 2: Wet Engine Compression Test
One of two problems is usually what's behind a low or zero compression value:
- The affected cylinder's piston rings are severely worn or damaged.
- The affected cylinder's intake/exhaust valves are severely worn or damaged.
The cool thing is we can do a wet compression test that'll tell us where the problem lies without having to tear the engine apart.
The wet compression test simply involves adding about two tablespoons of engine oil to the 'dead' cylinder and then retesting its compression.
If the cylinder's compression values goes up, you can conclude that the low/zero compression issue is due to worn piston rings.
If the cylinder's compression value does not go up, you've got cylinder head valve problems in that affected cylinder.
These are the test steps:
- 1
Add 1 or 2 tablespoon of engine oil in the cylinder you need to retest. I suggest using a small and long funnel so that the oil will reach the inside of the cylinder.
- 2
Install the compression gauge on the cylinder you just added oil to.
- 3
Have your helper crank the engine till the needle stops climbing on the compression gauge.
- 4
You'll see one of two results:
1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
2.) The needle will not move at all or stay at the same number you recorded earlier.
What ever value your compression tester reads, write it down again. - 5
Repeat steps 1 thru' 4 on any other cylinder you need to check.
Let's examine your test results:
CASE 1: The compression value of the cylinder you added oil to increased. This test result tells you that the low or near 0 PSI compression value is due to worn out piston rings of that specific cylinder.
CASE 2: The compression value of the cylinder you added oil to DID NOT increase. This test result confirms that the cylinder head valves of that cylinder are worn-out or damaged.
If this info saved the day, buy me a beer!
