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Power Balance Testing How To

cylinder head

One of the more useful diagnostic tests you can perform to narrow down an issue in an engine is with a power balance test. This test checks each cylinder in the engine for power output to make sure that they are all producing equal amounts of power.

There are several safety issues involved in this type of testing, especially if it's being done on an older model vehicle on which a scan tool or computer cannot be used to cancel cylinder firing for the test. Significant amounts of voltage can be involved in manually disconnecting spark during a power balance test, so every precaution towards safety should be taken.

The most basic way to conduct this test is to unplug spark and/or coil packs from each cylinder one at a time. Methodically going from one cylinder to the next, listening to the RPM drop the engine will have when that cylinder stops producing power. The cylinder that doesn't change the engine's RPM levels is the problem cylinder. In some cases, this is enough to show you the problem cylinder. At that point, the problem is very likely to be spark or fuel delivery.

When disconnecting each cylinder, keep it disconnected for about two seconds, then re-connect, wait another couple of seconds, and go to the next. The pauses and speed keep the engine from dying and too much unburnt fuel from entering the exhaust.

More complex power balance testing can be done with more sophisticated shop equipment.

There are also more sophisticated ways to do this same test, especially on vehicles where the danger of incurring injury from the spark is higher. Those more complex tests will be left for explanation on another day.