Engine Cylinder Power Balance Test Explained

A cylinder power balance test helps you find which cylinder is not contributing enough power to the engine, causing performance issues such as engine misfire or lack of power. The balance power test will point out if a cylinder is weak and not contributing its share to the total engine output. The power balance test can be performed on any vehicle, including 4, 6, 8, 10, and 12-cylinder engines, with the YOUCANIC full system scanner.

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We see the engine power balance tests performed more often on 6-cylinder, V8, and V12 engines, as those engines typically have fewer issues when only one cylinder is underperforming. In contrast, on a four-cylinder engine, the engine and car will often shake if you have one underperforming cylinder.

On a V8, V10, or V12 engine, sometimes all you notice is an engine that is intermittently missing when idling, and in some cases, that miss can be hard to notice, especially if the check engine light is not on.

What is a cylinder power balance test?

Each cylinder should contribute equal power to make up the engine’s total power output in a healthy engine. The total output of an engine is equal to the sum of power produced by the individual cylinders. The cylinder power balance test considers the cylinder’s effect on engine speed to determine power.

Suppose the engine is running. A spark plug or fuel injector is disabled while the engine is running, which prevents the spark plug from firing that cylinder. Engine speed should decrease when the cylinder is not firing, therefore, not contributing to the engine power output. The decrease in engine speed (RPMs) is recorded and compared to the drops that occur when the other cylinders are disabled. If one of the other cylinders of an engine produces a lower engine RPM drop, then you have found the cylinder that has a problem.

The starting point is finding which cylinder is not contributing to the engine’s total power output. When one of the cylinders is not contributing as much power as the other cylinder, a mechanical, electrical, or fuel supply problem is affecting the cylinder to produce less power than the rest.

An engine power balance test is an engine diagnostic procedure used to determine if all the cylinders are working well. The power balance test checks if all the cylinders are contributing equal power.

A power balance test is performed by disabling one cylinder at a time while measuring the drop in engine speed (RPMs). Cylinders can be disabled by turning off fuel injectors one at a time.

Symptoms

• The engine may miss at idle
• Check engine light may be on (not always)
• Engine shaking at idle
• Difficult accelerating

How do you perform a power balance test?

You can use an advanced diagnostic scanner such as the YOUCANIC scanner to perform a power balance test. You can cancel one cylinder at a time and monitor the RPM drop during the procedure. While it is possible to perform this test without any tools, an advanced scanner can help you monitor and graph the RPMs as you disable one cylinder at a time.

You can perform a power balance test in a couple of different ways. The easiest way is with YOUCANIC full system scan tool. Some vehicle manufacturers have preprogrammed the ECU to carry a power balance test, while others do not. Don’t worry; with the YOUCANIC scanner, you can carry out the power balance test regardless of whether the car manufacturer has this program in the ECU.

You should see the RPMs drop when you disable one of the cylinders. The RPM drop should have the same effect as you disable each cylinder. The two most common ways to disable one cylinder from misfiring are to disable one of the ignition coils or fuel injectors if each cylinder has its injector. Disabling fuel injectors is the preferred method, so you don’t send raw fuel to the catalytic converter and cause problems. As a cylinder is disabled, you must monitor the RPM drops from the idle speed of 800-1000 RPM.

1. Plug the YOUCANIC scanner into the OBD2 port under the dashboard.
2. Turn on the scanner and ignition, then select Maintenace on the scanner.
3. Select Power Balance from the menu.
4. Select your make and model or Smart VIN.
5. Run Power Balance Test.

The test under Maintenace is mainly for Ford and Mazda vehicles with power balance tests programmed in their ECUs. If your vehicle is not listed under the cylinder power balance test menu, follow these steps:

1. Locate the injector for each cylinder or the spark plugs.
2. Use the YOUCANIC scanner to disable one injector at a time.
3. Record the engine RPMs and power output as you unplug each cylinder.
4. Repeat the process for each cylinder.
5. Compare the power output for each cylinder to determine if there are any imbalances or issues with the performance of the cylinders.
6. One cylinder’s engine RPM drop will be less than the others, which means that the particular cylinder does not contribute enough power to the engine output; therefore, something is wrong with that particular cylinder.

It is important to follow the manufacturer’s recommendations and guidelines when performing a cylinder power balance test and to use caution when working on an engine. If you are not comfortable or experienced with working on vehicles, it is recommended to have a mechanic perform the test.

Performing Cylinder Power Balance Test without a Scan Tool

It is possible to perform a cylinder power balance test without a scanner, but you must be extremely careful so that you don’t get shocked or injured during the procedure.  In addition, monitoring the RPMs without a scan tool is more challenging. 

It is not a difficult task if you have a coil-on-plug design type, meaning each cylinder has an individual ignition coil. Unplug each coil one by one and check for RPM drop. Assuming you do not have a coil-on-plug type, you can remove the spark plug boots one by one. You need to be careful doing this, as you may cause a considerable shock if you’re not careful. To prevent getting shocked is to use a pair of plastic pliers.

Also, injectors still send fuel to that cylinder when you perform the power balance test without a scan tool and disconnect the spark plug. The raw fuel hits the catalyst unburned and self-ignites in the catalytic converter. When you run a power balance test by disconnecting the spark plugs, especially if you do so for a long time, you risk causing damage to the catalytic converter.

Troubleshooting Tips

Once you have identified the underperforming cylinder, the next step is to find out why. There are a few things that you should check. For several possible issues, a cylinder may not output as much power as the other cylinders. Some common problems that can lead a cylinder not to perform well include:

• Faulty spark plugs
• Bad ignition coil
• Vacuum leaks
• Ignition Problme3s
• Fuel pressure issue
• Lifter or valve issue
• Mechanical problems
• Blown head gasket
• Cracked head or block

Sometimes the problem may affect more than one cylinder. If that is the case, the cause could be several other issues, such as:

• Dirty mass air flow sensor
• Faulty oxygen sensor
• Clogged catalytic converter
• Electrical wiring issue
• Defective Engine Control unit (ECU)

Several issues can cause an engine to be off balance, and troubleshooting the problem will depend on the specific symptoms and underlying cause.

Here are some steps you can take to troubleshoot an engine that is misfiring:

1. Check the spark plugs and spark plug wires to ensure they are in good condition and properly connected.
2. Check the fuel system to ensure it is functioning properly and delivering the correct amount of fuel to the cylinders.
3. Check the air filter to make sure it is clean and not clogged.
4. Check the exhaust system for any leaks or blockages.
5. Check the engine’s ignition system to ensure that the ignition coils and control module are functioning properly.
6. Check the compression of each cylinder to ensure that the engine is not experiencing any issues with sealing or compression.
7. If you are still experiencing issues after checking these items, you may need to consult the manufacturer’s service manual or a mechanic for further troubleshooting and diagnosis.

It is important to use caution when working on an engine and follow the manufacturer’s recommendations and guidelines when troubleshooting a malfunctioning engine. If you are not comfortable or experienced with working on vehicles, it is recommended to have a mechanic perform the troubleshooting and repairs.

Spark Plugs / Ignition Coil

Place a spark plug tester inline between the ignition coil and spark plugs. While the engine is running, the spark plug tool should spark. Repeat this procedure for each spark plug.

The quick and dirty method was to remove the spark plug and connect it to the ground to check the spark, but this method can be risky and cause injuries if not performed properly.

Injector

Use a stethoscope on the fuel injector for the underperforming cylinder and listen if you can hear it. Click. If the injector doesn’t click like the rest, that fuel injector is faulty. It may not be a good test if the vehicle has DIRECT fuel injection.

Compression

If you have determined that one cylinder is not contributing enough power to the engine output, use a compression and cylinder leakage test to determine if the problem is due to a compression issue.

Compression problems quite often are caused due to burned valves but also can be due to excessive carbon build-up on the valves. Other possible causes include worn piston rings, timing issues, and damaged valves.

Oxygen Sensors

If you are having issues with cylinders \underperfrming on one side of the engine (bank one or bank 2), but the other side is performing well, the problem could be a corresponding faulty bank oxygen sensor 1. The bank one sensor one and bank two sensor 1 data is used by the Engine Control Unit (ECU) to adjust the stochiometric ratio or, as it is commonly known, the fuel-air ratio. If data from the upstream oxygen sensor is wrong, the ECU will cause the engine to run too rich or lean.

Oxygen sensors are not the other issue that can cause one bank to run rough; other possible causes include a clogged catalytic converter or faulty mass air flow (MAF) sensor if the vehicle uses two MAF sensors.

Frequently Asked Questions

Additional Resources

1. Cylinder power balance test – autoedu.info
2. Cylinder Balance Test – freeasestudyguides.com
3. SOLVING AUTOMOTIVE PERFORMANCE ISSUES – ericthecarguy.com
4. MASTERING THE BASICS: COMPREHENSIVE ENGINE TESTING – motor.com