Gxt Ferret 54 ENGINE DIAGNOSTIC CENTER Manuel d'utilisateur télécharger pdf (Page 47)

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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.

Follow the manufacturer's procedure for

putting the engine controller in "open loop"

mode. Some common ways are:

• The idle speed motor may have to be

unplugged if the test is done at idle.

• Disconnecting the coolant temperature

sensor will usually cause the computer

to operate in open-loop fuel control as if

the engine were cold.

• Where the oxygen sensor is easily

reached it can be unplugged to lockup

the fuel control.

• Timing can usually be fixed by

disconnecting the MAP sensor hose, or

as on Fords, pulling the timing test plug.

• EGR valves should be disabled by

removing and plugging the vacuum hose

to the valve.

• On some engines there is a running test

mode, set through the diagnostic

connector, that lets the test run without

interaction effects.

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.

THIS TEST CAUSES UNBURNED FUEL TO BE

PASSED

INTO THE EXHAUST. CATALYTIC

CONVERTERS BURNING THIS FUEL WILL

BECOME

HOTTER. REPEATING THE TEST

FREQUENTLY

MAY CAUSE EXCESSIVE HEAT

UNDER

THE CAR.

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