Vehicle Testing Procedures
6-3
Testing Under Load
When sampling exhaust gases, NO readings can be observed at
idle, low speeds and low load operating conditions. However, since
NO is mainly formed under load (high combustion chamber
temperatures), effective testing must be performed under load
using a chassis dynamometer or by driving on the road.
Using a chassis dynamometer, the vehicle weight must be
considered and the appropriate normal road load horsepower
(NRLHP) applied to simulate the changing load applicable to a
vehicle when driven on a level road. The drive to collect data may
be to accelerate, cruise or decelerate as necessary in order to
operate the vehicle under conditions that aid in:
•
Identifying emission failure areas,
•
Reducing emissions in general, and
•
Locating/correcting drive ability problems.
Interpreting the data monitored is the same in each case. Consider
the information in the theory and interpretation sections of this
manual to aid the diagnosis. Consider also, the vehicle owners
complaint and/or the symptoms that relate to the complaint. Drive
ability and emissions symptoms can consist of the following, or
combinations of the following:
•
Will not crank,
•
Cranks, will not start,
•
Hard starting,
•
Malfunction indicator lamp on,
•
Engine stalls,
•
Hesitation, sag, stumble, and or
•
Lack of power, sluggish or spongy,
•
Surge, chuggle,
•
Engine miss or cut out,
•
Backfire,
•
Spark knock, detonation,
•
Engine noise,
•
Excessive exhaust emissions or fails emission test,
•
Poor fuel economy,
•
Incorrect idle,
— high
— rough
— unstable
•
Jumps, jerks,
•
Excessive exhaust odor,
•
Excessive exhaust smoke,
•
Fuel odor, and/or
•
Dieseling, run on.
Diagnosis may require using a variety of specific tests and test
equipment, depending on the drivers complaint and/or the
symptoms related to the complaint. If a combination of complaints/
faults are involved, consider the devices and factors that could
possibly affect those areas. Remember, one device/factor may
affect several areas; and/or, several devices/factors may affect one
area.
To Next Page
Loading...