GMC chevrolet camaro 2000 Service Manual page 79

0-68 Vibration Diagnosis and Correction
8. If the vibration still exists, inspect the propeller
shaft runout.
9. If the vibration still exists, inspect the harmonic
balancer.
10. If the vibration still exists, the problem is related to
residual engine imbalance. Refer to the
procedure below.
Excessive Inherent Engine Firing Frequency
183028
Firing frequency is a term used to describe the pulses
created as the engine fires in each cylinder. All
engines have a firing frequency. The intention here is
to keep these disturbances from entering the
passenger compartment. Initially, inspect for the
following conditions:
• The engine and the exhaust system are mounted
in the correct position.
• All of the mounts and hangers are in good
condition and are correct for the application.
.. No components, hoses, or lines are grounding to
the frame or to the body.
The frequency of these disturbances will depend on
the number of cylinders. The engine order will always
be equal to one-half the number of cylinders. This
is because a four-stroke engine requires two complete
revolutions of the crankshaft in order to fire all of
the cylinders.
For example, a V6 engine will fire cylinders 1, 3,
and 5 on the first revolution. Cylinders 2, 4, and 6 will
fire on the second revolution. This results in
three firing pulses per revolution of the crankshaft.
General Information
Engine Vibration Diagnosis with the EVA
INPUT A INPUT B
95611
i. Place the EVA vibration sensor on the seat track
rail with the UP label facing upward.
2. Plug the EVA into a 12 volt power supply.
3. Prepare the EVA for data recording:
3.1. Press RECORD
3.2. Select a snapshot tag number
3.3. Press ENTER in order to begin recording
4. Slowly accelerate until the vibration occurs.
5. Note the vehicle speed and the engine RPM
where the disturbance occurs.
6. Press ENTER on the EVA in order to record the
vibration data.
7. Perform the road test diagnoses in order to
determine engine-speed or vehicle-speed
sensitivity. Refer to Road Test.
Engine Firing Frequency Symptoms
" The vibration may be torque sensitive.
.. The vibration is engine-speed related.
" The vibration is heard as a boom or a moan.
" The vibration is felt as a shake, roughness or buzz
(depending on the number of cylinders).
.. The vibration affects the resonance of a system or
a component, causing the system or the
component to have a narrow RPM range.
The key to correcting these types of complaints is to
isolate the vibration from the passenger compartment
or the body.
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