Isuzu Trooper (1998-2002 year). Manual — part 370
6A–10
ENGINE MECHANICAL (6VE1 3.5L)
Engine Lacks Power
Condition
Possible cause
Correction
Trouble in fuel system
Fuel Pressure Control Valve not
working normally
Replace
Fuel injector clogged
Clean or replace
Fuel pipe clogged
Clean
Fuel filter clogged or fouled
Replace
Fuel pump drive circuit not working
normally
Correct or replace
Fuel tank not sufficiently breathing
due to clogged Evaporative
Emission Control System circuit
Clean or replace
Water in fuel system
Clean
Inferior quality fuel in fuel system
Use fuel of specified octane rating
Powertrain Control Module supplied
poor voltage
Correct circuit
Throttle Position Sensor cable
broken or poor connections
Correct or replace
Throttle Position Sensor defective
Replace
Mass Airflow Sensor not working
normally
Replace
Manifold Absolute Pressure Sensor
not working normally
Replace
Intake Air Temperature Sensor not
working normally
Replace
Engine Coolant Temperature Sensor
circuit open or shorted
Correct or replace
Engine Coolant Temperature Sensor
defective
Replace
Powertrain Control Module defective
Replace
Trouble in intake or exhaust system
Air Cleaner Filter clogged
Replace filter element
Air duct kinked or flattened
Correct or replace
TWC defective
Repair
Ignition failure
————
Refer to Hard Start Troubleshooting
Guide
Heat range of spark plug inadequate
Install spark plugs of adequate heat
range
Ignition coil defective
Replace
6A–11
ENGINE MECHANICAL (6VE1 3.5L)
Condition
Correction
Possible cause
Engine overheating
Level of Engine Coolant too low
Replenish
Fan clutch defective
Replace
Incorrect fan installed
Replace
Thermostat defective
Replace
Engine Coolant pump defective
Correct or replace
Radiator clogged
Clean or replace
Radiator filler cap defective
Replace
Level of oil in engine crankcase too
low or wrong engine oil
Change or replenish
Resistance in exhaust system
increased
Clean exhaust system or replace
defective parts
Throttle Position Sensor adjustment
incorrect
Replace with Throttle Valve ASM
Throttle Position Sensor circuit open
or shorted
Correct or replace
Cylinder head gasket damaged
Replace
Engine overcooling
Thermostat defective
Replace (Use a thermostat set to
open at 82
°
C (180
°
F))
Engine lacks compression
————
Refer to Hard Start
Others
Tire inflation pressure abnormal
Adjust to recommended pressures
Brake drag
Adjust
Clutch slipping
Adjust or replace
Level of oil in engine crankcase too
high
Correct level of engine oil
Exhaust Gas Recirculation Valve
defective
Replace
6A–12
ENGINE MECHANICAL (6VE1 3.5L)
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
j
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
g
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
i
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 (6VE1 3.5L)
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
Exhaust system defective
Repair or Replace
Drive belt slipping
Replace auto tensioner or drive belt
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