Hard A/C lines in contact with the shock tower can conduct all manner of engine noises to the customer's ear through the
car body.
|
There's a lot going on between the road we're traveling and the hood of our cars, and with all the dynamics related to brakes,
suspension, steering and wind turbulence, noise-hunting isn't for the lazy or faint-hearted. Some technicians take to it like
a fish takes to water and actually enjoy searching for elusive clicks, pops, whines or rumbles. But what do you charge somebody
for chasing a noise that can sometimes gobble up most of a day? Noise problems, whether they're real or perceived, can be
extremely elusive, telegraphing themselves from one part of the car to another with annoying intermittence.
Let's narrow the focus of all those noises to what Ford calls "Noise, Vibration and Harshness, (NVH)" because vibration and
noise can be closely related. Noise is defined as an abnormal sound. Vibration is a trembling sensation that is usually tied
to engine or road speed. Harshness is related to the way a vehicle rides.
Simply shoving the purge solenoid under the suction line like this on a Jeep Cherokee amplifies the solenoid's thumping sound
to the point where it sounds like an engine knock.
|
Noise is generated in various frequencies (low to high pitch), and when noise impacts our eardrums, we tend to sort out those
auditory inputs and compare them to what we recognize as normal. There are sticklers who see a monster failure waiting behind
every little squeak and rattle, and there are people who don't notice anything short of a roadside bomb.
One critical element of noise-hunting is to make sure that the noise you're chasing is the one the customer's complaining
about, or else you might spend an afternoon fixing a problem that would annoy the heck out of you but wasn't even related
to their concern, and then you have to start all over. Believe me, it can happen! I've done it more than once. The Mustang Buzz
I drew a work order on a late 1990s Mustang when I was the drivability tech at a Ford dealer, and the customer concern was
a buzzing noise that seemed to be originating from the instrument cluster area at highway speeds. In the days of mechanical
speedometers, I would have gone in the direction of lubing the cable, but this unit was blessed with a cable-free electronic
analog speedometer.
Dry steering stops like this one (left) will cause odd squeaks and pops if the wheels are turned tightly while driving on
rough surfaces.
|
It wasn't long before I was kind of stymied, but then the shop foreman discovered that the buzzing wasn't audible if he took
a windbreaker jacket he found in the back seat and held it between his head and the sun visor area while the buzz was at its
worst. That sent us to the point of taping up the chrome trim with masking tape (wind turbulence rattles loose trim sometimes),
but the noise remained unchanged.
Finally, the discovery was made that the very same buzzing could be felt on the end of the owner's finger when he had his
fingers just outside the driver's window.
Conclusion: The aerodynamic bug shield was creating a high frequency disturbance in the wind that was picked up by the windshield,
amplified and projected downward to the speedometer area, which, by default, had been perceived as the originator.
Here's the progression: Typically, noises have an originator, a conductor and a reactor. In this case, the originator was
the bug shield, the conductor was (by way of the air) the windshield and the reactor was the area around the speedometer head.
The reactor is the noticeably affected component. With a vibration, the reactor might be a sun visor, the seat, the steering
wheel, etc.
