Isuzu Amigo / Axiom / Trooper / Rodeo / VehiCross. Service manual — part 1352
6A–12
ENGINE MECHANICAL (6VD1 3.2L)
Engine Noisy
Abnormal engine noise often consists of various noises
originating in rotating parts, sliding parts and other
moving parts of the engine. It is, therefore, advisable to
locate the source of noise systematically.
Troubleshooting Procedure for Crankshaft Journals or Crankshaft Bearing Noise
Condition
Possible cause
Correction
Noise from crank journals or from
crank bearings
(Faulty crank journals and crank
Oil clearance increased due to worn
crank journals or crank bearings
Replace crank bearings and
crankshaft or regrind crankshaft and
install the undersize bearing
y
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bearings usually make dull noise that
becomes more evident when
accelerating)
Crankshaft out of round
Replace crank bearings and
crankshaft or regrind crankshaft and
install the undersize bearing
Crank bearing seized
Crank bearing seized Replace crank
bearings and crankshaft or regrind
crankshaft and install the undersize
bearing
Troubleshooting Procedure for Connecting Rods or Connecting Rod Bearing Noise
Short out each spark plug in sequence using insulated
spark plug wire removers. Locate cylinder with defective
bearing by listening for abnormal noise that stops when
spark plug is shorted out.
Condition
Possible cause
Correction
Noise from connecting rods or from
connecting rod bearings
(Faulty connecting rods or
Bearing or crankshaft pin worn
Replace connecting rod bearings
and crankshaft or regrind crankshaft
pin and install the undersize bearing
y
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connecting rod bearings usually
make an abnormal noise slightly
higher than the crank bearing noise,
which becomes more evident when
Crankpin out of round
Replace connecting rod bearings
and crankshaft or regrind crankshaft
pin and install the undersize bearing
which becomes more evident when
engine is accelerated)
Connecting rod bent
Correct or replace
g
)
Connecting rod bearing seized
Replace connecting rod bearings
and crankshaft or regrind crankshaft
pin and install the undersize bearing
Troubleshooting Procedure for Piston and Cylinder Noise
Abnormal noise stops when the spark plug on the cylinder
with defective part is shorted out.
Condition
Possible cause
Correction
Piston and cylinder noise
(Faulty piston or cylinder usually
k
bi
d
h
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l
Piston clearance increased due to
cylinder wear
Replace piston and cylinder body
makes a combined mechanical
thumping noise which increases
Piston seized
Replace piston and cylinder body
g
when engine is suddenly accelerated
but diminishes gradually as the
Piston ring broken
Replace piston and cylinder body
but diminishes gradually as the
engine warms up)
Piston defective
Replace pistons and others
Troubleshooting Procedure for Piston Pin Noise
Short out each spark plug and listen for change in engine
noise.
Condition
Possible cause
Correction
Piston pin noise
(Piston makes noise each time it
goes up and down)
Piston pin or piston pin hole worn
Replace piston, piston pin and
connecting rod assy
6A–13
ENGINE MECHANICAL (6VD1 3.2L)
Troubleshooting Procedure for Slapping or Hitting etc Noise
The slapping sound stops when spark plug on bad
cylinder is shorted out.
Condition
Possible cause
Correction
Timing belt noise
Timing belt tension is incorrect
Replace pusher or adjust the tension
pulley or replace timing belt
Tensioner bearing defective
Replace
Timing belt defective
Replace
Timing pulley defective
Replace
Timing belt comes in contact with
timing cover
Replace timing belt and timing cover
Valve noise
Valve clearance incorrect
Replace adjusting shim
Valve and valve guide seized
Replace valve and valve guide
Valve spring broken or weakened
Replace
Valve seat off–positioned
Correct
Camshaft worn out
Replace
Crankshaft noise
Crankshaft end play excessive
(noise occurs when clutch is
engaged)
Replace thrust bearing
Engine knocking
Preignition due to use of spark plugs
of inadequate heat range
Install Spark Plugs of adequate heat
range
Carbon deposits in combustion
chambers
Clean
Fuel too low in octane rating
Replace fuel
Wide Open Throttle enrichment
system failure
Refer to Section 6E
Selection of transmission gear
incorrect
Caution operator of incorrect gear
selection
Engine overheating
Refer to “Engine Lacks Power”
Others
Water pump defective
Replace
Drive belt slipping
Replace auto tentioner or drive belt
6A–14
ENGINE MECHANICAL (6VD1 3.2L)
Abnormal Combustion
Condition
Possible cause
Correction
Trouble in fuel system
Fuel pressure control valve defective
Replace
Fuel filter clogged
Replace
Fuel pump clogged
Clean or replace
Fuel tank or fuel pipe clogged
Clean or replace
Fuel injector clogged
Clean or replace
Fuel pump relay defective
Replace
Power supply cable for fuel pump
broken or poor connections
Reconnect, correct or replace
Mass Airflow (MAF) Sensor circuit
open or defective
Correct or replace
MAF Sensor defective
Replace
Manifold Absolute Pressure Sensor
circuit open or shorted
Correct or replace
Manifold Absolute Pressure Sensor
defective
Replace
Engine Coolant Temperature (ECT)
Sensor circuit open or shorted
Correct or replace
ECT Sensor defective
Replace
Throttle Position Sensor adjustment
incorrect
Readjust
Throttle Position Sensor defective
Replace
Throttle Position Sensor connector
poor connections
Reconnect
Vehicle Speed Sensor cable poor
connections or defective
Correct or replace
Vehicle Speed Sensor loosely fixed
Fix tightly
Vehicle Speed Sensor in wrong
contact or defective
Replace
Powertrain Control Module cable
poor connections or defective
Correct or replace
Trouble in emission control system
Heated Oxygen Sensor circuit open
Correct or replace
Heated Oxygen Sensor defective
Replace
Signal vacuum hose loosely fitted or
defective
Correct or replace
EGR Valve circuit open or shorted
Correct or replace
Exhaust Gas Recirculation Valve
defective
Replace
ECT Sensor circuit open or shorted
Correct or replace
Canister Purge Valve circuit open or
shorted
Correct or replace
Canister Purge Valve defective
Replace
ECT Sensor defective
Replace
Positive Crankcase Ventilation
(PCV) valve and hose clogged
Correct or replace
Evaporator system
Refer to Section 6E
Trouble in ignition system
————
Refer to “Engine Lacks Power”
6A–15
ENGINE MECHANICAL (6VD1 3.2L)
Condition
Correction
Possible cause
Trouble in cylinder head parts
Carbon deposits in combustion
chamber
Remove carbon
Carbon deposit on valve, valve seat
and valve guide
Remove carbon
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