6-4
Vehicle Testing Procedures
On-Road and Dynamometer Testing Under Load
Exhaust emission testing with a chassis dynamometer can be
performed in the same way a stationary vehicle is tested in the
shop bay, except that the engine operates under load, simulating
operating conditions on the road, except for traffic, turning corners
and weather conditions.
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Prolonged use of the analyzer in conjunction with a
dynamometer and a hot-running vehicle under load may
damage the sample probe and affect readings.
On-road testing provides “real world” information about a vehicle.
However, on-road testing requires two people one to drive and one
to monitor the analyzer display. On-road testing also offers less
than ideal test conditions since the sample probe may fall out of
the tail pipe if not secured properly and it may be difficult to
achieve the desired drive cycle due to traffic and weather
conditions.
Drive Cycles
A drive cycle is a specific, repeatable pattern of acceleration,
cruise, deceleration and idle is followed. The following drive cycles
may be used:
•
90 Second Drive Cycle,
•
Hard Acceleration Drive Cycle,
•
High Cruise Drive Cycle, or
•
On-Board Diagnostic (OBD) II Drive Cycle.
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The 90 Second, Hard Acceleration, and High Cruise
Drive Cycles are typically used for drive ability testing
where a repeatable drive pattern is helpful.
1. Position the analyzer inside the vehicle such that a person
other than the driver can control and monitor the display.
2. Route the sample hose and probe and the clear plastic
vapor vent hose out a partially open window.
— Although a vehicle moving down the road develops
very little condensation and the air stream flowing
across the open vent hose end dilutes vapors
immediately, it may be necessary to add an extension
to the vapor vent hose to help prevent corrosive
condensation damage to the vehicle surface.
3. Route the sample hose and probe along the vehicle body
and insert the probe into the vehicle tail pipe. Make sure
that the sample probe is fully inserted.
4. Secure and support the sample hose along the vehicle
body. Use duct tape about 30" (75 cm) long, folded in half
and taped to itself, wrap the tape around the hose once or
twice at the middle of the tape. Position the tape ends
through a partially open window, door and/or trunk lid and
tie several loose knots with the tape and shut the opening
onto the tape.
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