GxT V055-01 Diagnostic Analyzer - Manual (Page 15)

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Power Balance - Automatic/Manual
On distributor engines, power balance, or each cylinder’s
power contribution relative to the others, can be seen by
turning off the spark plugs one at a time and measuring
the drop in RPM. In Automatic mode, the Diagnostic
Center will suppress ignition to each cylinder in turn, and
will display and save the starting and ending RPM for
each. The more RPM decrease seen, the more a cylinder
must have been contributing. If all cylinders are contributing equally, RPM drops will be consistent among
cylinders. If a cylinder shows only 1/3 of the drop of the average cylinder, it should be checked further
with the other EngineLink tests. If all drops are very low, see the facing page for advice on defeating idle
compensators which may be raising idle speed in response to the suppression.
The test relies upon steady timing, fixed air-fuel feed and a constant amount of engine drag during the
test to make valid comparisons between all of the cylinders. If the RPM drifts during the test, a message
will appear, indicating the test should be run again.
A steady drag on the engine can improve the test results. Turning the heater fan on high and headlights
on bright is usually the best method. Particular attention should be directed to eliminating loads that can
turn on or off in the middle of the test such as the air conditioner compressor and radiator fan motor.
Operating the engine above the controlled idle RPM will minimize the effects of idle compensators and
put the engine at a smoother operating point. RPMs of 1000 to 2500 are suitable for the test. Listen to
the sound of the engine as suppression is applied. A large initial RPM drop is a good indicator of a strong
cylinder.
On non-computerized engines the timing, fuel mix and idle setting do not vary with time. However, active
control systems may have to be put in open-loop mode to keep the timing and fuel mixture fixed, so that
the test results do not end with minimal % Drops.
After the test, carefully restore the disengaged parts. Service codes may be set during the test, but they
will usually clear automatically after 50 to 100 starts.
Low power cylinder problems are associated with spark plugs and wires, piston rings, valves and valve
springs, vacuum leaks, fuel unbalance, head gaskets, and EGR problems. If a cylinder test produces a
higher RPM it may be from crossed spark plug wires, an open intake valve, leaking EGR, or an engine
computer effect.
The results of this test, if compared to the Electronic Compression and Ignition Secondary tests, can
provide additional clues about the cause of poor cylinder performance.
Manual Mode
Manual suppression can be used to listen for noise changes in an individual cylinder that may give clues
about the problem.
To suppress ignition in an individual cylinder, choose Manual Suppression from the POWER menu and
SELECT the cylinder you want to suppress. Press NEXT to suppress ignition to that cylinder.