Doing a manual cylinder balance test will ‘nail down’ the misfiring cylinder (also known as a ‘dead’ cylinder) that's causing your 1.6L Toyota Corolla (1.6L Geo Prizm) to idle rough.
Why perform a manual cylinder balance test? The short answer is to save time, frustation and money in trying to find and solve the exact cause of your Corolla's (Prizm's) engine rough idle or engine miss. This applies particularly to the non-OBD II Corollas that don't have misfire diagnostics. Even if your Toyota is OBD II equipped, there are times the PCM can't or doesn't pin-point the misfiring cylinder.
This is when a manual cylinder balance test saves the day and gets you closer to solving the misfire problem.
Cylinder Balance Test
The purpose behind the cylinder balance test is to ‘short’ one cylinder at a time while the engine is running.
If the cylinder you're ‘shorting’ is ‘dead’ (misfiring), then ‘shorting’ won't affect (worsen) the engine's idle. If the cylinder IS NOT ‘dead’ to begin with... then ‘shorting’ WILL cause your Corolla's engine's idle to worsen.
What makes doing the cylinder balance test sooo easy is the fact that the fuel injector electrical connectors are very accessible, since these are the ones we need to disconnect and reconnect (one at a time) to ‘short’ the cylinder.
Here's what you'll need to do:
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.
Disconnect one fuel injector at a time.
What you're looking out for is the fuel injector that DOES NOT make the engine's idle worse (when you unplug it from it's connector). If this happens... then this cylinder is the ‘dead’ one.
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 noticeable!
Identify the cylinder that's ‘dead’ using the illustration at the beginning of this tutorial.
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 pin-pointed 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.