Troubleshooting Noises
From Your Car (Is Your Car Trying to Tell You Something?)
Troubleshooting those weird noises coming from your car can help you
determine needed repairs. It's important that you listen to what your
car is trying to tell you.
Although many people
still use the old broomstick-held-to-the-ear method of zeroing in
on noises, the best method these days is a stethoscope. Indispensable
in finding the source of a sound, it's also a lot easier to place
it where you want it than the clunky end of a broomstick.
Here are a few general
guidelines to what your car's noises might mean:
BANG: A sharp,
startling sound, like a rifle shot, means you're dealing with the
dreaded backfire. You'll probably be able to trace this to something
that's causing a rich air/fuel mixture.
In the past you might
have zeroed in on a heavy carb float, but today think about faulty
signals from coolant temp or O2 sensors. The catalytic converter may
also be damaged.
Another possibility is
a clogged monolithic converter blowing through. This will only occur
once and will be accompanied by an amazing increase in power. If your
car has air injection, perhaps the diverter valve is no longer diverting.
BOOM: A hollow,
low-frequency sound/sensation, this makes you feel as if you're riding
inside a metal drum and the atmospheric pressure is rapidly changing
between positive and negative.
On rear wheel-drive cars,
check out the driveshaft and its u-joints because if it's spinning
out-of-true, it will cause waves that push up on the floor of your
car.
BUZZ: An annoying
"bzzzzzzzzz" sound, like a trapped insect, can usually be
traced to unfortunate positioning of interior trim parts. Have somebody
else drive while you press, pry and pound on every likely spot.
CHIRP: This sounds
like birds are nesting under your hood. You can probably blame a maladjusted
or misaligned belt, but don't ignore the idler pulley. Or, it could
just be your tires when you hit second gear.
CLANG or CLANK:
This sound couldn't possibly be emitted by any light, flimsy parts.
It's coming from a heavy, essential component, such as a set of gears.
A good example is the sound a bad rear axle pinion bearing makes when
you drop the transmission into Drive, then Reverse.
CLICK or CLACK:
This sounds like 007 working the slide of his Beretta automatic. When
in an engine, it's typically repeated rhythmically.
With OHV, perhaps a stuck
lifter is allowing clearance in the pushrod/rocker valve, or maybe
a solid lifter is just out of adjustment. On carbureted cars, check
out the fuel pump before you start opening up the motor.
When emanating from the
nether regions of the front end during a turn, this sound may be traced
to an outboard CV joint.
CLUNK: A heavy
bumping sound, softer than a clang, usually indicates you should look
at suspension bushings, including shock or strut mounts. Or how about
a loose strut gland nut?
FLAPPING: If it's
not due to a colony of bats under the hood, maybe a belt's coming
apart. Fan interference is another possibility. Regardless, this is
a visual inspection sort of thing.
GRINDING: A horrible,
torturous sound, like a bad dentist would make while working with
obsolete equipment, means something's going awry - and fast.
If it occurs when the
brakes are applied, either the linings are gone or you've got one
of those unpleasantly-aggressive friction material formulas that tend
to eat rotors.
GROAN: Something's
dry, probably a suspension component. If it's metal, it's going to
break really soon. If it's rubber, try some silicone lube.
GRUNT: Again,
a dry joint somewhere in the underpinnings is likely. If it's in the
stoppers, suspect rear drum shoes contaminated with brake fluid or
gear lube from a defunct axle seal.
HISS: If it's
continuous and changes with rpms, it may be normal belt noise. Otherwise,
a slow leak in the cooling system is likely. A black light will help
you find this.
HUM: We don't
mean what the radio does between stations, but the noise a differential
or wheel bearing makes. If it responds to acceleration/deceleration,
suspect the differential. Then look into the bearings. Unfortunately,
it's often very difficult to tell which side (or even which end) the
hum's coming from.
KNOCK: Like knuckles
on a wooden door, this sound is deep and hollow. Often it's a warning
that something important (and expensive) is about to let go.
It's unfortunate that
a loose pin sounds pretty much the same as a defunct rod bearing,
but with a little patience you should be able to determine what's
at fault.
First, check idle oil
pressure even if you have to screw in a mechanical gauge. If it's
low, you can bias your decision toward bearings.
Next, listen with your
stethoscope. A rod bearing makes more noise at the oil pan than elsewhere,
and a wrist pin more racket up on the water jacket. Hold RPMs at 2500,
jerk the throttle open and let it snap closed. This will accentuate
rod knock, whereas pin noise won't change very much.
Now's the time to starting
shorting out cylinders. A bad pin will quiet down, but a rod knock
will double its cadence.
Finally, you can pull
the pan for a visual inspection. If the bearings are good, you know
you've got a pin problem.
PING: Sort of
like little ball bearings being poured on a tin roof, this sound is
detonation (aka spark knock) - a phenomenon in which the air/fuel
charge explodes violently instead of burning smoothly.
There are many potential
causes here from clogged EGR passages and overheating to excessive
spark advance and, with spark knock suppression, a defunct detonation
sensor. Hook up your timing light then tap on the engine near the
sensor to see if the spark retards.
POP: This sounds
like a shotgun being fired through a mattress. It usually means the
engine's coughing back through the intake.
A sticking or leaking
valve is a distinct possibility, as is jumped valve timing, particularly
with a belt-driven OHC.
Then there's ignition,
which may be firing way too early due to a twisted distributor, cap/rotor/wire
problems, a faulty position sensor or a breakdown in the module.
Also, if your car's running
quite lean, opening the throttle to lots of cold air can induce this
reaction.
RATTLE: They didn't
coin the term "rattle trap" for nothing, you know. People
have been fighting this annoying noise since the automobile was invented.
Thanks to plastics, better
rubbers and more highly engineered fasteners, rattles are less prevalent
than they once were. But you'll still get them, usually in the undercarriage
somewhere. Likely culprits include exhaust system parts, calipers
or loose brake pads.
ROAR: If it's
not something obvious like a blown exhaust system, maybe the transmission
is never shifting into high or overdrive.
With a manual transmission,
the clutch might be slipping. Fan clutches usually fail by never engaging,
not the opposite, but it's still a possibility.
If it's general road
noise, you could switch to less aggressive tires or add undercoating
to your car.
RUMBLE: While
a pleasant enough throaty sound when it's from a free-flowing exhaust
system, it can easily cross over into the unacceptable sound range.
But don't choke the power down with an overly restrictive cheap muffler.
For tire and road noise, see "ROAR".
SCRAPING: Something
like "jeet-jeet-jeet-jeet" that speeds up as the car gathers
speed probably means an object of one sort or another is contacting
the driveshaft, possibly an exhaust shield or hanger or the parking
brake cable. Your brake system, especially drum hardware, is also
a distinct possibility.
SCREECH: "SQUEAL"
taken to the max. See "SQUEAL".
SIZZLING: Like
the sound of bacon frying, this is usually only audible with the engine
off. Oil may be leaking onto the exhaust manifold or a minor coolant
seepage may be occurring.
SQUEAL: This sound
is usually related to brakes and belts. On the former, maybe you're
down to the pad wear indicators. Or the discs and semi-metallic linings
aren't getting along due to poor rotor finishing or washing, an assembly
error, a troublesome friction formula or the like. Squealing is certainly
common in disc brakes, but clunking can also occur on initial application
if the shoes are loosely mounted.
In the case of belts,
check if they are loose, worn or contaminated.
TAP: Much the
same as a click, sort of like beating on the intake manifold with
a screwdriver blade, this is usually valvetrain-related. Think about
stuck lifters or an adjustment that provides too much lash.
WHINE: Not what
an impatient 3-year old does but just as annoying. This is a hard
one to pin down, but it's apt to come from worn ball or roller bearings,
mismatched gears, too light a lube in a manual gearbox (ATF, maybe?)
or alternator bushings getting ready to go.
WHIR: The sound
made by happy mechanicals. It's one of the few noises you probably
shouldn't worry about.
WHISTLE: Usually
occurring at higher speeds, it's probably wind noise. But do double
check if the latches and tumblehome are properly adjusted. Are the
body gaskets in good shape?
Article source:
http://www.autohausaz.com
