GxT Ferret 54 ENGINE DIAGNOSTIC CENTER - Manual (Page 77)

TESTS
PCV VALVE
The PCV valve routes blowby gases from
the crankcase to the carburetor or intake
manifold to be mixed with intake air.
Malfunctions or clogging of the valve or
attached hoses and fittings will affect the air/
fuel mixture. To test the valve, note the CO
reading, then remove the valve from the
valve cover, leaving it attached to the hose
leading to the intake manifold or carburetor
base. While the valve is drawing fresh air,
the O2 level should rise and CO level should
drop by 1 to 1.5%. If there is no change, the
PCV could be malfunctioning. Run the
engine above 2000 RPM. Plug the end of
the valve with your thumb. You should feel
vacuum pressure, and the reading should
return to original levels. If there is no
vacuum or no change in reading, look for a
clogged valve, fitting, or hose.
If the CO reading drops by more than 1.5%,
the crankcase oil could be contaminated
with fuel. In this case, carefully “sniffing” the
oil fill hole with the sample hose should
result in an HC reading over 750 ppm. Care
must be taken to prevent contaminating
the probe by touching any oil or grease.
Possible causes of crankcase contamination
are:
• Excessive blowby due to poor overall
mechanical condition.
• Leaky fuel injectors
• Excessive fuel pressure
• Carburetor has a sticky choke or a
leaking inlet needle or seat.
Once the problem has been corrected,
change the oil and continue tests. Air/fuel
mixture adjustments should not be
attempted while the oil is fuel contaminated.
CANISTER PURGE SYSTEM
The vapor canister and purge system is
designed to store fuel vapors from the fuel
tank or carburetor in an activated charcoal
filled canister for later burning by the engine.
When the purge is active, a valve allows
manifold vacuum from the engine to pull air
through the canister and thereby draw out
the stored vapors to be burned.
Take a reading of the O2. Then disable the
canister purge system and compare the new
O2 reading.
• If the O2 increases more than a couple
of tenths of a percent, then the system,
when active, had been allowing excess
fuel in.
• A similar decrease would indicate that
the system had been allowing excess air
to pass.
• If there is no change in the reading, the
system is probably functioning correctly.
AIR INJECTION SYSTEM
The air injection system provides excess
oxygen to the exhaust system to allow
continued burning of excess fuel in the
exhaust stream. Heat, unburned fuel and the
added air allow continued burning in the
exhaust stream. The result is a reduction of
HC and CO emissions.
To test the system, run the engine and take
a measurement, noting the level of CO2 and
O2. Disable the Air Injection System and take
a new measurement. The O2 should drop
2-3% because less O2 is entering the
system. If no change occurs, either the Air
Injection system was not completely disabled
or it was not functioning properly.
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