Cylinder Power Balance Test
A cylinder power balance test tests each cylinder's effectiveness compared to the others. A weak cylinder typically results from the ignition, fuel delivery, a vacuum leak, or a mechanical problem, such as a faulty valve or worn piston rings. A faulty head gasket, cracked cylinder head or block will cause an RPM drop on adjacent cylinders.
For many years, removing a plug boot from its plug was standard procedure. The problem is a prolonged open in the secondary ignition system may cause damage to the coil or ignition module. Sometimes a sensor, like an O2 sensor, will need to be disconnected so the computer will not try to compensate for the sudden change in conditions.
Check with the manufacturer's specifications before proceeding and remember safety first. Use a grabber or a tool to prevent any shock that may result from removing the plug cover.
Notice the RPM drop while removing spark or fuel from the cylinder. If a cylinder's RPM drop is not consistent with the others, this indicates a problem with that cylinder. Each cylinder is tested at a certain speed of around (800-1000 RPM). An engine analyzer tests each cylinder and then compares the results; if no engine analyzer is available, record the test results with a pencil and paper.
An engine analyzer or dedicated tool is best for testing coil over plug (COP) ignition systems. Some vehicles are sensitive; coil damage may result from removing a coil from its spark plug while the engine is running. Check with the manual, and there are many ways to cancel a cylinder, such as disconnecting the associated fuel injector or coil connector. Some handheld scanners are capable of canceling cylinders, allowing the technician to monitor RPM drop easily.