Ford Falcon. Manual — part 9
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Noise, Vibration and Harshness
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DIAGNOSIS AND TESTING (Continued)
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Noise, Vibration and Harshness
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DIAGNOSIS AND TESTING (Continued)
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Noise, Vibration and Harshness
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DIAGNOSIS AND TESTING (Continued)
The engine speed is an important factor in arriving
1: Customer Interview
at a final conclusion. Therefore, connect an
The diagnostic process starts with the customer
accurate tachometer to the engine, even if the
interview. The service advisor must obtain as much
vehicle has a tachometer. Use a tachometer that
information as possible about the concern and take a
has clearly defined increments of less than 50
test drive with the customer. There are many ways a
rpm. This ensures an exact engine speed reading.
customer will describe NVH concerns and this will
help minimize confusion arising from descriptive
4: Verify the Customer Concern
language differences. It is important that the concern
Verify the customer concern by carrying out a road
is correctly interpreted and the customer descriptions
test, an engine run-up test, or both.
are recorded. During the interview, ask the following
The decision to carry out a road test, an engine
questions:
run-up test, or both depends on the type of NVH
When was the concern first noticed?
concern. A road test may be necessary if the
Did the concern appear suddenly or gradually?
symptom relates to the suspension system or is
Did any abnormal occurrence coincide with or
sensitive to torque. A drive engine run-up (DERU) or a
proceed its appearance?
neutral engine run-up (NERU) test identifies noises
and vibrations relating to engine and drivetrain rpm.
Use the information gained from the customer to
Remember, a condition will not always be identifiable
accurately begin the diagnostic process.
by carrying out these tests, however, they will
2: Pre-Drive Check
eliminate many possibilities if carried out correctly.
It is important to do a pre-drive check before road
5: Road Test
testing the vehicle. A pre-drive check verifies that the
NOTE: It may be necessary to have the customer ride
vehicle is relatively safe to drive and eliminates any
along or drive the vehicle to point out the concern.
obvious faults on the vehicle.
During the road test, take into consideration the
The pre-drive check consists of a brief visual
customer’s driving habits and the driving conditions.
inspection. During this brief inspection, take note of
The customer’s concern just may be an acceptable
anything that will compromise safety during the road
operating condition for that vehicle.
test and make those repairs or adjustments before
taking the vehicle on the road.
The following is a brief overview of each test in the
order in which it appears. A review of this information
3: Preparing for the Road Test
helps to quickly identify the most appropriate process
necessary to make a successful diagnosis. After
Observe the following when preparing for the road
reviewing this information, select and carry out the
test:
appropriate test(s), proceeding to the next step of this
Review the information recorded on the NVH
process.
Diagnostic Guide. It is important to know the
The Slow Acceleration Test is normally the first
specific concern the customer has with the
test to carry out when identifying an NVH concern,
vehicle.
especially when a road test with the customer is
Do not be misled by the reported location of the
not possible.
noise or vibration. The cause can actually be
The Heavy Acceleration Test helps to determine if
some distance away, transferred from another
the concern is torque-related.
part of the vehicle.
The Neutral Coast Down Speed Test helps to
Remember that the vibrating source component
determine if the concern is vehicle speed-related.
(originator) may only generate a small vibration.
This small vibration can in turn cause a larger
The Downshift Speed Test helps to determine if
vibration or noise to emanate from another
the concern is engine speed-related.
receiving component (reactor), due to contact with
The Steering Input Test helps to determine how
other components (transfer path).
the wheel bearings and other suspension
Conduct the road test on a quiet street where it is
components contribute to a vehicle speed-related
safe to duplicate the vibration or noise. The ideal
concern.
testing route is an open, low-traffic area where it
The Brake Test helps to identify vibrations or
is possible to operate the vehicle at the speed in
noise that are brake-related.
which the condition occurs.
The Road Test Over Bumps helps isolate a noise
If possible, lower the radio antenna in order to
that occurs when driving over a rough or bumpy
minimize turbulence. Identify anything that could
surface.
potentially make noise or be a source of wind
The Engine Run-Up Tests consist of the Neutral
noise. Inspect the vehicle for add-on items that
Run-up Test and the Engine Load Test. These
create vibration/noise. Turn off the radio and the
heating and cooling system blower.
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Noise, Vibration and Harshness
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DIAGNOSIS AND TESTING (Continued)
tests help to determine if the concern is engine
Downshift Speed Test
speed-related.
To carry out this test, proceed as follows:
The Neutral Run-up Test is used as a follow-up
Shift into a lower gear than the gear used when
test to the Downshift Speed Test when the
carrying out the Slow Acceleration Test.
concern occurs at idle.
Drive at the engine rpm where the concern
The Engine Load Test helps to identify
occurs.
vibration/noise sensitive to engine load or torque.
The concern is engine speed related if duplicated
It also helps to reproduce engine speed-related
while carrying out this test. This eliminates the
concerns that cannot be duplicated when carrying
tyres, wheels, brakes and the suspension
out the Neutral Run-up Test or the Neutral Coast
components as sources.
Down Test.
If necessary, repeat this test using other gears
The Engine Accessory Test helps to locate faulty
and NEUTRAL to verify the results.
belts and accessories that cause engine
speed-related concerns.
Proceed as necessary.
The Vehicle Cold Soak Procedure helps to
Steering Input Test
identify concerns occurring during initial start-up
and when an extended time lapse occurs between To carry out this test, proceed as follows:
vehicle usage.
Drive at the speed where the concern occurs,
while making sweeping turns in both directions.
Slow Acceleration Test
If the concern goes away or gets worse, the
To carry out this test, proceed as follows:
wheel bearings, hubs, U-joints (contained in the
Slowly accelerate to the speed where the reported
axles of 4WD applications), and tyre tread wear
concern occurs. Note the vehicle speed, the
are all possible sources.
engine rpm and, if possible, determine the
Proceed as necessary.
vibration frequency.
Brake Test
Attempt to identify from what part of the vehicle
the concern is coming.
To carry out this test, proceed as follows:
Attempt to identify the source of the concern.
Warm the brakes by slowing the vehicle a few
Proceed as necessary.
times from 80–32 km/h (50–20 mph) using light
braking applications. At highway speeds of 89–97
Heavy Acceleration Test
km/h (50–60 mph), apply the brake using a light
pedal force.
To carry out this test, proceed as follows:
Accelerate to 89–97 km/h (55–60 mph).
Accelerate hard from 0-64 km/h (0-40 mph).
Lightly apply the brakes and slow the vehicle to
Decelerate in a lower gear.
30 km/h (20 mph).
The concern is torque-related if duplicated while
A brake vibration noise can be felt in the steering
carrying out this test.
wheel, seat or brake pedal. A brake noise can be
Proceed as necessary.
heard upon brake application and diminish when
Neutral Coast Down Speed Test
the brake is release.
To carry out this test, proceed as follows:
Road Test Over Bumps
Drive at a higher rate of speed than where the
To carry out this test, proceed as follows:
concern occurred when carrying out the Slow
Drive the vehicle over a bump or rough surface
Acceleration Test.
one wheel at a time to determine if the noise is
Place the transmission in NEUTRAL and coast
coming from the front or the back and the left or
down past the speed where the concern occurs.
the right side of the vehicle.
The concern is vehicle speed-related if duplicated
Proceed as necessary.
while carrying out this test. This eliminates the
engine and the torque converter as sources.
Neutral Engine Run-up (NERU) Test
If the concern was not duplicated while carrying
To carry out this test, proceed as follows:
out this test, carry out the Downshift Speed Test
Install a tachometer.
to verify if the concern is engine speed-related.
Increase the engine rpm up from an idle to
Proceed as necessary.
approximately 3,500 rpm while in PARK on front
wheel drive vehicles with automatic transmissions,
or NEUTRAL for all other vehicles. Note the
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