Subaru Impreza 3 / Impreza WRX / Impreza WRX STI. Service manual — part 87
ME(STI)-110
Engine Trouble in General
MECHANICAL
3. Low output, hesitation and
poor acceleration
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Loosened or cracked intake duct
A
Loosened or cracked PCV hose
A
Loosened or cracked vacuum hose
B
Defective intake manifold gasket
B
Defective throttle body gasket
B
Defective PCV valve
B
Loosened oil filler cap
B
Dirty air cleaner element
A
Fuel line
Defective fuel pump and relay
B
Clogged fuel line
B
Lack of fuel or insufficient fuel
C
Timing belt
Defective timing
B
Compression
Incorrect valve clearance
B
Loosened spark plug or defective gasket
B
Loosened cylinder head bolt or defective cylinder head
gasket
B
Improper valve sealing
B
Defective valve stem
C
Worn or broken valve spring
B
Worn or stuck piston rings, cylinder and piston
C
Incorrect valve timing
A
Improper engine oil (low viscosity)
B
Lubrication system
Incorrect oil pressure
B
Cooling system
Over-heating
C
Over-cooling
C
Others
Evaporative emission control system malfunction
A
Symptoms
Problem parts etc.
Possible cause
RANK
ME(STI)-111
Engine Trouble in General
MECHANICAL
4. Surging
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Loosened or cracked intake duct
A
Loosened or cracked PCV hose
A
Loosened or cracked vacuum hose
A
Defective intake manifold gasket
B
Defective throttle body gasket
B
Defective PCV valve
B
Loosened oil filler cap
B
Dirty air cleaner element
B
Fuel line
Defective fuel pump and relay
B
Clogged fuel line
B
Lack of fuel or insufficient fuel
C
Timing belt
Defective timing
B
Compression
Incorrect valve clearance
B
Loosened spark plug or defective gasket
C
Loosened cylinder head bolt or defective cylinder head
gasket
C
Improper valve sealing
C
Defective valve stem
C
Worn or broken valve spring
C
Worn or stuck piston rings, cylinder and piston
C
Incorrect valve timing
A
Improper engine oil (low viscosity)
B
Cooling system
Over-heating
B
Others
Evaporative emission control system malfunction
C
5. Engine does not return to
idle.
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Loosened or cracked vacuum hose
A
Others
Stuck or damaged throttle valve
A
6. Dieseling (Run-on)
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Cooling system
Over-heating
B
Others
Evaporative emission control system malfunction
B
7. After burning in exhaust
system
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Loosened or cracked intake duct
C
Loosened or cracked PCV hose
C
Loosened or cracked vacuum hose
B
Defective PCV valve
B
Loosened oil filler cap
C
Timing belt
Defective timing
B
Compression
Incorrect valve clearance
B
Loosened spark plug or defective gasket
C
Loosened cylinder head bolt or defective cylinder head
gasket
C
Improper valve sealing
B
Defective valve stem
C
Worn or broken valve spring
C
Worn or stuck piston rings, cylinder and piston
C
Incorrect valve timing
A
Lubrication system
Incorrect oil pressure
C
Cooling system
Over-cooling
C
Others
Evaporative emission control system malfunction
C
Symptoms
Problem parts etc.
Possible cause
RANK
ME(STI)-112
Engine Trouble in General
MECHANICAL
8. Knocking
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Loosened oil filler cap
B
Timing belt
Defective timing
B
Compression
Incorrect valve clearance
C
Incorrect valve timing
B
Cooling system
Over-heating
A
9. Excessive engine oil con-
sumption
Intake system
Loosened or cracked PCV hose
A
Defective PCV valve
B
Loosened oil filler cap
C
Compression
Defective valve stem
A
Worn or stuck piston rings, cylinder and piston
A
Lubrication system
Loosened oil pump attaching bolts and defective gas-
ket
B
Defective oil filter gasket
B
Defective crankshaft oil seal
B
Defective rocker cover gasket
B
Loosened oil drain plug or defective gasket
B
Loosened oil pan fitting bolts or defective oil pan
B
10. Excessive fuel consump-
tion
Engine control system <Ref. to EN(H4DOTC)(diag)-2, Basic Diagnostic Procedure.>
A
Intake system
Dirty air cleaner element
A
Timing belt
Defective timing
B
Compression
Incorrect valve clearance
B
Loosened spark plug or defective gasket
C
Loosened cylinder head bolt or defective cylinder head
gasket
C
Improper valve sealing
B
Defective valve stem
C
Worn or broken valve spring
C
Worn or stuck piston rings, cylinder and piston
B
Incorrect valve timing
B
Lubrication system
Incorrect oil pressure
C
Cooling system
Over-cooling
C
Symptoms
Problem parts etc.
Possible cause
RANK
ME(STI)-113
Engine Noise
MECHANICAL
26.Engine Noise
A: INSPECTION
*
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 discon-
nected.
*
• 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 discon-
nected.
*
• 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
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