GxT Ferret 54 ENGINE DIAGNOSTIC CENTER - Manual (Page 84)

High HC combined with High NOx indicates
a lean misfire. Oil being burned will also raise
the temperature and cause NOx formation.
Possible causes are:
• Lean fuel delivery
• EGR system
• Oil burning due to:
Rings
Valves
Guides
High HC combined with High O2 indicates
there is unburned fuel because of a misfire.
Since air is composed of about 21% Oxygen,
each cylinder that misses will add about:
21%
Number of Cylinders in the Engine
For example, one cylinder misfiring in a 6
cylinder engine would add approximately
3.5% oxygen to the exhaust stream (21%
divided by 6 cylinders).
The catalytic converter may mask the HC
portion, but the increase in O2 will still be
observed. It is important that the air injection
system supplying excess O2 to the converter
be disabled during testing so that the O2
reading can be used for diagnosis. Possible
causes are:
•
Ignition misfire
• Misfire from mechanical problems
High CO combined with Low O2 indicates
there is a rich mixture. Possible causes are:
• Problems in the air intake system
• PCV problem
• Improperly set mixture
• Malfunction of vapor canister
High HC combined with High CO and High
NOx indicates there is a complete
breakdown in the emission control system.
If the catalytic converter is functioning at all,
it is overwhelmed by emissions at the
exhaust manifold. Possible causes are:
• Catalytic Converter
• ECM
• Sensors
• Wiring
Low CO2 (<10%) generally indicates a bad
air fuel ratio, either rich or lean.
• When combined with High CO (>0.5%)
and High O2 (higher than CO reading),
the catalytic converter is not burning CO
to form O2.
• When combined with High CO (>0.5%)
and Low O2 (lower then CO reading),
the catalytic converter is probably not the
problem. Possible causes are:
Air intake restriction
Fuel delivery problems
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