6-1
Vehicle Testing
Procedures
Testing Gasoline-Fueled Vehicles
Diagnosis from the exhaust gas sample can be difficult on an
engine that has any combination of the following systems:
•
Catalytic converter,
•
Computer control with an O
2
sensor and fuel injection,
•
Air management,
•
Exhaust gas recirculation,
•
Evaporative emission control,
•
Electronic spark timing, electronic spark control or both,
•
Positive crankcase valve (PCV), and
•
Distributorless ignition.
Multiple sensors and specific conditions affect each of these
systems and the list of probable causes for abnormal exhaust
concentrations provides so many variations that a different
approach must be used to interpret the readings. For additional
information, refer to
Chapter 7–Diagnostic Technique
and
Data
Analysis Guidelines
.
Testing Propane-Fueled Vehicles
Test vehicles with propane-fueled engines using the same
techniques and information described for testing gasoline-fueled
engines with the following exceptions:
•
Typ ic al CO readings at idle are 1-1.5% vol. More than 3% vol is
not acceptable.
•
At cruise speed, typical CO readings are about 1% vol. More
than 2% vol is not acceptable.
•
1% vol CO is equal to an air-fuel ratio of about 14.6:1.
•
2% vol CO is equal to an air-fuel ratio of about 14:1.
•
Typ ic al HC readings at idle are 50–250 ppm.
6
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