Isuzu KB P190. Manual — part 502
6-8 ENGINE DIAGNOSIS (C24SE)
Condition Possible
cause Correction
Engine overheating
Level of Engine Coolant too low
Replenish
Thermo switch or fan motor
defective
Replace
Thermostat
defective
Replace
Engine Coolant pump defective
Correct or replace
Radiator clogged
Clean or replace
Radiator filter cap defective
Replace
Level of oil in engine crankcase
too low or wrong oil in engine
Change or replenish
Resistance in exhaust system
increased
Clean exhaust system or replace
defective parts
Throttle Position Sensor
adjustment incorrect
Adjust Wide Open Throttle switch
setting
Throttle Position Sensor circuit
open or shorted
Correct or replace
Cylinder head gasket damaged
Replace
Cooling Fan clutch defective
Replace
Fan belt slipping
Adjust tension of V-belt or replace
V-belt
Engine overcooling
Thermostat defective
Replace (Use a thermostat set to
open at 92
°C (197.6°F))
Engine lacks compression
-
Refer to Hard Start
Others
Tire inflation pressure abnormal
Adjust to recommend pressures
Brake
drag
Adjust
Clutch slipping
Adjust or replace
Level of oil in engine crankcase
too high
Correct level of engine oil
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.
Condition Possible
cause Correction
Noise from crank journals or from
crank bearings
(Faulty crank journals and crank
bearings usually make dull noise
that becomes more evident when
accelerating)
Oil clearance increased due to
worn crank journals or crank
bearings
Replace crank bearings and
crankshaft or regrind crankshaft
and install the over size bearing
Crankshaft out of round
Replace crank bearings and
crankshaft or regrind crankshaft
and install the over size bearing
Crank bearing seized
Replace crank bearings and
crankshaft or regrind crankshaft
and install the over size bearing
ENGINE DIAGNOSIS (C24SE) 6-9
Abnormal Noise Due to Hydraulic Lash Adjuster
Should abnormal noise due to the hydraulic lash
adjuster trouble be heard immediately after the engine
is started, inspect as follows:
Condition Possible
cause Correction
Abnormal noise is heard
Air contaminated
Bleed
HLA is spongy
Check ball valve broken
Repair
Safety valve in cylinder head
broken
Replace
Valve clearance is not zero
HLA inside stick
Replace HLA assembly
Troubleshooting Procedure
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
connecting rod bearings usually
make an abnormal noise slightly
higher than the crank bearing
noise, which becomes more
evident when engine is
accelerated)
Bearing or crankshaft pin worn
Replace connecting rod bearings
and crankshaft or regrind
crankshaft and install the under
size bearing
Crankpin out of round
Replace connecting rod bearings
and crankshaft or regrind
crankshaft and install the under
size bearing
Connecting rod bent
Correct or replace
Connecting rod bearing seized
Replace connecting rod bearings
and crankshaft or regrind
crankshaft and install the under
size bearing
Troubleshooting Procedure
Abnormal noise stops when the spark plug on the
cylinder with defective parts is shorted out.
Condition Possible
cause Correction
Piston and cylinder
(Faulty piston or cylinder usually
makes a combined mechanical
thumping noise which increases
when engine is suddenly
accelerated but diminishes
gradually as the engine warms up)
Piston clearance increased due to
cylinder wear
Replace piston and cylinder body
Piston seized
Replace piston and cylinder body
Piston ring broken
Replace piston and cylinder body
Piston defective
Replace pistons and others
6-10 ENGINE DIAGNOSIS (C24SE)
Troubleshooting Procedure
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
Troubleshooting Procedure
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 wheels defective
Replace
Timing belt comes in contact with
timing cover
Replace timing belt and timing
cover
Valve noise
Valve and valve guide seized
Replace valve and valve guide
Valve spring broken
Replace
Valve seat off-positioned
Correct
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
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 or incorrect gear
selection
Engine overheating
Refer to "Engine Lacks Power"
Others
Water pump defective
Replace
V-belt slipping
Adjust tension of V-belt or replace
V-belt
ENGINE DIAGNOSIS (C24SE) 6-11
Abnormal Combustion
Condition Possible
cause Correction
Trouble in fuel injection 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
loosely connected or defective
Reconnect, correct or 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
Reconnect
Throttle Position Sensor defective
Replace
Throttle Position Sensor
connector loosely connected
Reconnect
Vehicle Speed Sensor cable
loosely connected or defective
Correct or replace
Vehicle Speed Sensor loosely
fixed
Fix tightly
Vehicle Speed Sensor in wrong
contact or defective
Replace
Engine Control Module cable
loosely connected or defective
Correct or replace
Trouble in emission control
system
Heated Oxygen Sensor circuit
open (If applicable)
Correct or replace
Heated Oxygen Sensor defective
(If applicable)
Replace
Signal vacuum hose loosely fitted
or defective
Correct or replace
ECT Sensor circuit open or
shorted
Correct or replace
ECT Sensor defective
Replace
Evaporative Emission Control
system (If applicable)
Refer to Section 6E
Trouble in ignition system
-
Refer to "Engine Lacks Power"
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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