A manual cylinder balance test will help you pinpoint the misfiring (or 'dead') cylinder that's causing your 1.8L Toyota Corolla (or 1.8L Geo Prizm) to idle rough.
Why perform this test? Simply put, identifying the misfiring cylinder is the most important first step when diagnosing a rough idle or engine misfire. Finding the exact cylinder at fault makes it easier to troubleshoot the root cause of the problem.
In the long run, this step saves you time, frustration, and money when tracking down and fixing the issue.
This test is especially useful for older, non-OBD II models that don't have built-in misfire diagnostics. Even if your Toyota is OBD II equipped, there are times when the PCM won't detect or pinpoint the misfiring cylinder.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 1.8L (4A-FE) Toyota Corolla: 1993, 1994, 1995, 1996, 1997.
- 1.8L Geo Prizm: 1993, 1994, 1995, 1996, 1997.
Cylinder Balance Test
The cylinder balance test involves 'shorting' one cylinder at a time while the engine is running.
'Shorting' a cylinder will have one of two effects:
- 'Dead' cylinder: If the cylinder is already misfiring (or 'dead'), then 'shorting' it won't make the engine idle any worse.
- Good cylinder: If the cylinder is working properly, 'shorting' it will make the engine idle worse.
We'll do this (the 'shorting') by simply disconnecting and reconnecting the cylinder's fuel injector from its electrical connector.
What makes this test so easy is that the fuel injector electrical connectors are easy to access.
Here's what you'll need to do:
- 1
Start the engine and let it idle.
NOTE: This test is done with the engine running. Be careful, stay alert, and think safety all of the time. - 2
Disconnect the cylinder #1 fuel injector.
- 3
Observe the engine idle. Does the engine idle become rougher?
If the cylinder is 'dead', unplugging the fuel injector WILL NOT make the engine's idle worse.
In a good cylinder (one that's contributing to engine power), when you unplug the fuel injector from its connector, the engine's idle will get worse -it's that noticeable! - 4
Reconnect the fuel injector.
- 5
Observe the engine idle. Does the engine idle improve?
In a good cylinder (one that's contributing to engine power), when you unplug the fuel injector from its connector, the engine's idle will get worse. When you reconnect the fuel injector, the engine idle improves. - 6
Repeat steps 2 thru 5 several times to make sure of your test result.
- 7
Identify the cylinder that's 'dead' using the illustration at the beginning of this tutorial.
- 8
Repeat steps 2 thru 7 on the remaining fuel injectors.
Let's take a look at what your cylinder balance test results mean:
CASE 1: Unplugging an fuel injector had NO EFFECT on the engine's idle. This test result confirms that that cylinder (this fuel injector belongs to) is 'dead' and causing a misfire.
Now that you have found the 'dead' cylinder, that's causing the misfire, your next steps are to see what's causing the problem.
This means that you need to check that the cylinder has spark, fuel and good compression.
CASE 2: Unplugging any of the fuel injectors (one at a time) had NO EFFECT on the engine's idle. This tells you that the misfire is affecting all 4 cylinders and more importantly, it tells you that all of the fuel injectors and fuel injectors are working as they should.
Since you have a rough idle condition that can not be pinpointed to just one or two cylinders, I suggest you check:
- Test engine compression. Check to see if compression between cylinders varies more than 15%.
- Vacuum leak from leaking intake manifold gaskets or vacuum hoses.
- Failing fuel pump that is not sending enough volume to the fuel injectors.
Although testing the above conditions is beyond the scope of this article, you now know in what direction you need to take your troubleshooting.
You Found The 'Dead' Cylinder, What Next?
Finding out which cylinder, in your 1.8L Toyota Corolla (1.8L Geo Prizm) is misfiring ('dead'), is half the battle in diagnosing the exact cause of the problem.
Now, you need to keep in mind that the cylinder is 'dead' because it's missing one of the following three things:
- Spark.
- Fuel.
- Air (compression).
The next step is to perform the tests to confirm if a lack of spark, or a lack of fuel, or a lack of compression is causing the problem with the cylinder.
This is what I would do and what I recommend:
- Check for spark:
- Check that the 'dead' cylinder is getting spark by checking the condition of the spark plug. Confirm that it isn't worn out, cracked/broken, or swimming in oil from a defective spark plug tube seal.
- Check that the 'dead' cylinder's spark plug wire is delivering spark with a dedicated spark tester.
- Check the fuel injector:
- Resistance test each fuel injector to see if any one of them is fried internally.
- Tutorial: How To Test The Fuel Injectors (1993-1997 1.8L Toyota Corolla).
- Check the fuel injector is receiving an activation signal. This test is done with Noid light.
- Tutorial: How To Use A Noid Light And Where To Buy It (at: easyautodiagnostics.com).
- Check engine compression:
- The 'dead' cylinder may have low or zero compression causing it misfire.
- Tutorial: How To Test Engine Compression (1993-2008 1.8L Toyota Corolla).
The problem causing the cylinder misfire can easily be figured out with this diagnostic strategy, always keep in mind that it's all a process of elimination -trying to figure what the cylinder is missing (spark, fuel, or compression).
The following articles may also be of help:
- Diagnosing A Toyota Corolla Misfire Case Study.
- Troubleshooting A Hard To Diagnose Misfire Case Study (GM 3.1L, 3.4L).
- Carbon Tracks Are A Common Cause Of Ignition Misfires (at: easyautodiagnostics.com).
Where To Buy The Tools You Need
Check out the following links and comparison shop the specific tools you'll need to diagnose the misfire (rough idle) on your 1.8L Toyota Corolla (1.8L Geo Prizm):
The best place to comparison shop and buy is online. I now buy all of my tools online to save.
More 1.8L Toyota Corolla Tutorials
There are several more 'how to' tutorials that I've written that are 1.8L Toyota Corolla specific, that may be of further help. You can find them here:
Here's a sample of the tutorials you'll find:
- TPS Idle Switch Multimeter Test (1993-1997 1.8L Toyota Corolla).
- How To Test The Throttle Position Sensor (1993-1997 1.8L Toyota Corolla).
- How To Do A Cylinder Balance Test (1993-1997 1.8L Toyota Corolla).
- How To Test For A Blown Head Gasket (1993-2008 1.8L Toyota Corolla).
If this info saved the day, buy me a beer!
