Gxt Ferret 54 ENGINE DIAGNOSTIC CENTER Manuel d'utilisateur télécharger pdf (Page 45)

The graph suggests how cylinder power differences affect the RPM during an engine cycle.

POWER DIFFERENCE WAVEFORM

A low power cylinder will show a negative power difference reading. Smooth running engines

have power difference readings less than 5. Dead cylinders usually read more than -15.

Low power cylinder problems are associated with worn or broken piston rings, valves and valve

springs, broken head gaskets, vacuum leaks, fuel imbalance, spark plugs and wires 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.

To gain experience with typical engines, we suggest that, while you are testing a good engine,

short out a spark plug to see the effect of a dead cylinder.

The readings are taken from the RPM during each cylinder’s power stroke, and adjusted to

give somewhat similar readings for most engines. Look for consistency among cylinders.

Engines with eight or more cylinders may show a weak cylinder in a later position than actual.

For example, a weak #4 cylinder could appear as #5. Engines with particularly heavy flywheels,

for their displacement, may show the effects of a weak cylinder spread across two or three

subsequent cylinders. Engines made with staggered timing patterns will show large difference

readings when they are working correctly. For example: six cylinder engines built from an eight

cylinder block.

12 34

Cylinder

Sequence

RPM

3-108-1

Power

Reading

4-16

1 2 ... 40 41 42 43 44 45 46 47 48 49 50 ... 101 102

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Gxt Ferret 54 ENGINE DIAGNOSTIC CENTER Manuel d'utilisateur Page 45