Engine Power Balance Testing – Total Power Output Of The Engine

Engine Power Balance Testing - Total Power Output Of The Engine
Engine Power Balance Testing - Total Power Output Of The Engine

The engine power balance test, can be a great way to pinpoint a cylinder, that’s under performing.

Most importantly, a cylinder that is not working as well as, the other cylinders in the engine.

The engine power balance test measures, the power that a particular cylinder contributes, to the total power of the engine.

The engine power balance test, uses the cylinder’s effect on the engine’s speed, to determine this power.

So, while the engine is running, either a spark plug or primary circuit is grounded. As a result, this prevents the spark plug from firing in the cylinder, which prevents combustion in that cylinder.

Cylinder Power Balance Test
Cylinder Power Balance Test

Consequently, engine speed should decrease, when the cylinder is inoperative. Next, record the drop in speed and compare it to the other cylinders. So, if all the cylinders produce the same amount of power, all engine rpm drops would be the same.

But, if  the drop in engine speed, becomes much more for that cylinder, than for the other cylinders. As a result, the engine will run rough. Because, one or more cylinders, are not producing as much power as the others.

As A Result, The Engine Power Balance Test, Identifies The Less Productive Cylinders.

Also, If the engine has an (EGR) valve, the vacuum line must be disconnected and plugged. Changes in engine vacuum, may cause the (EGR) valve to cycle on and off. This can very the engine speed and interfere with the readings.

The cylinder power balance test is quick and easy to perform. But, the results of this test alone, do not specify, where the problem is.

Therefore, you need to compare these results, to the results of a compression test and cylinder leakage test:

  • The compression test determines, the maximum pressure in the cylinder, on the compression stroke.
  • The cylinder leak down test, measures how well the cylinder seals.
Testing Compression And Cylinder Leak Down
Testing Compression And Cylinder Leak Down

Finally, by comparing the results of each test to each other, you can identify, what may be the problem.

If The Results Of The Tests Show That It Has:

  • Good compression
  • Proper leakage
  • Good power balance

A leaking cylinder, would not be the cause of the imbalance. The fuel system of most engines is common to all cylinders. And, therefore would not cause a engine power balance problem.

Other Things That Might Cause The Problem Are:

  • A non-common system
  • An ignition problem (typically in the secondary)
  • A vacuum leak that does not affect all cylinders

Mechanical Failure Or Defect:

  • Bent Pushrod
  • Broken Rocker Arm
  • Worn Camshaft Lobe
  • Collapsed Hydraulic Lifter

Furthermore, all these faults do not affect the sealing of the cylinder. But, do affect the opening of the valves.

Camshaft Damage
Camshaft Damage

So, to determine the exact cause of the poor imbalance, one should test the ignition system. Consequently, an engine with good compression, good power balance, and excessive cylinder leakage, is typically an evenly worn high-mileage engine. An engine with poor compression, proper leakage and good power balance, usually has a valve timing problem.


Use the combination of results for further testing from:

So, many things can cause a weak cylinder. And, it may take some time, to pinpoint the engines exact problem. Also, one possibility may be, a leaking head gasket. Finally, they make a testing fluid that can confirm this problem, by testing for the presence of hydrocarbons.

Thank You !