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Troubleshooting those weird noises coming from your Jaguar
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 Jaguar'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 Jaguar'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 Jaguar.
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 jaguarble 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? |