1
Chapter
A
GENERAL DIAGNOSIS
Poor engine performance can be the result of a long list
of problems. Performance, or driveability problems may
be indicated by customer complaints of no starting,
hard starting, loss of power, poor fuel mileage, engine
knock, or engine misfire. Begin diagnosis by getting
specific information from the customer. Find out the
exact nature of the problem, under what conditions it
occurs, and when the symptoms first started.
CUSTOMER INTERVIEW
This first step in the process is crucial to diagnosing au-
tomotive concerns as it helps you get a clear under-
standing of the situation. Use the following procedures
to begin every diagnosis:
• Verify the concern
• Research the history of the concern
• Ask the customer what they think the problem is
• Verify the information you have gathered
One of the most important steps in diagnosis is to veri-
fy the customer's concern. Often a driver's description
lacks some of the information necessary to begin prop-
er diagnosis. You might misunderstand the driver's de-
scription or the symptom may be caused by circum-
stances that you might not encounter during a typical
operation check or test drive.
The best solution is for the driver to demonstrate the
problem for you or the service advisor. If that is not prac-
tical, question the driver about exactly when the prob-
lem occurs. This information can lead you to drive the
vehicle under the same conditions and with an opera-
tional check, you can verify the concern and begin to
move to the proper subsystem to begin your diagnosis.
A rational diagnostic procedure must be followed to
successfully diagnose a customer's complaint. By fol-
lowing logical procedures you can use your time more
efficiently and replace or repair the right components.
Improper diagnosis leads to come-backs, dissatisfied
customers, a waste of your time and your customer's
time.
Before attempting to repair a performance problem,
make sure the engine is in sound mechanical condition.
In addition to internal engine defects, driveability prob-
lems may be caused by a malfunction in the electrical,
fuel, ignition, or emission control systems. Accurate
troubleshooting information for the vehicle being ser-
viced is essential for testing and evaluating all systems.
After determining that there is a driveability problem,
take a systematic approach to solving it. Work in a log-
ical manner to not only repair the problem, but also elim-
inate any other conditions that may have contributed to
the failure. To diagnose performance problems, follow
these four steps:
• Preliminary inspection
• Road test
• Review vehicle service history and applicable sup-
port materials
• Comprehensive engine testing
PRELIMINARY INSPECTION
Eliminate any obvious problems by performing an
under-hood inspection. The source of noise or vibration
complaints will often be revealed by a visual inspection.
Problems such as rough running or stalling may be
caused by a broken or disconnected vacuum hose or
electrical wire. When performing an inspection, check
for the following:
• Drive belts that are properly tensioned and free of
cracks, frayed edges, and glazing
• Electrical connections that are secure and clean. In-
spect harnesses for signs of brittle insulation, rub-
bing, and broken or damaged wires
• Engine-mounted accessories that are properly sup-
ported; look for loose or missing bolts, worn bush-
ings, and loose or broken support brackets
• Engine mounts, torque struts, and vibration
dampers that are in good condition and securely at-
tached
• Hoses, water and vacuum, that are tight and prop-
erly routed. Replace any that are loose, brittle,
kinked, broken, or otherwise damaged
Содержание ASE-A8
Страница 2: ......