Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Manual - part 182
ME(w/o STI)-109
Engine Noise
MECHANICAL
26.Engine Noise
A: INSPECTION
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When disconnecting the fuel injector connector, the malfunction indicator light illuminates and DTC is stored in ECM memory.
Type of sound
Condition
Possible cause
Regular clicking sound
Sound increases as engine
speed increases.
• Valve mechanism is defective.
• Incorrect valve clearance
• Worn camshaft
• Broken valve spring
Heavy and dull clank
Oil pressure is low.
• Worn crankshaft main bearing
• Worn connecting rod bearing (large end)
Oil pressure is normal.
• Loosened flywheel mounting bolt
• Damaged engine mounting
High-pitched clank
Sound is noticeable when
accelerating with an overload
condition.
• Ignition timing advanced
• Accumulation of carbon inside combustion chamber
• Wrong heat range of spark plug
• Improper octane value gasoline
Clank when engine speed is
between 1,000 and 2,000
rpms.
Sound is reduced when the fuel
injector connector of the noisy
cylinder is disconnected.
*
• Worn crankshaft main bearing
• Worn connecting rod bearing (large end)
Knocking sound when engine
is operating under idling
speed and engine is warm
Sound is reduced when the fuel
injector connector of the noisy
cylinder is disconnected.
*
• Worn cylinder liner and piston ring
• Broken or stuck piston ring
• Worn piston pin and hole at piston end of connecting rod
Sound is not reduced if each
fuel injector connector is dis-
connected in turn.
*
• Unusually worn valve lifter
• Worn cam sprocket
• Worn camshaft journal bore in cylinder head
Squeaky sound
—
• Insufficient generator lubrication
Rubbing sound
—
• Poor contact of generator brush and rotor
Gear scream when starting
engine
—
• Defective ignition starter switch
• Worn gear and starter pinion
Sound like polishing glass
with a dry cloth
—
• Loose V-belt
• Defective water pump shaft
Hissing sound
—
• Insufficient compression
• Air leakage in air intake system, hose, connection or manifold
Timing belt noise
—
• Loose timing belt
• Timing belt contacting with adjacent part
Valve noise
—
• Incorrect valve clearance