Isuzu N-Series. Service manual — part 548
SERVICE INFORMATION 00-7
Excessive Fuel Consumption
Excessive Oil Consumption
Overheating
Checkpoint
Possible cause
Correction
Fuel system
Fuel leakage
Repair or replace the fuel system related
parts
Air cleaner
Clogged air cleaner element
Clean or replace the air cleaner element
Idling speed
Poorly adjusted idling speed
Adjust the idling speed
Injection nozzle
Injection nozzle injection starting pressure
too low
Improper spray condition
Adjust or replace the injection nozzle
Fuel injection timing
Fuel injection timing improperly
Adjust the fuel injection timing
Injection pump
Defective Delivery valve resulting is fuel
drippage after fuel injection
Replace the delivery valve
Valve clearance
Valve clearance improperly adjusted
Adjust the valve clearance
Compression pressure
Blown out cylinder head gasket. Worn cyl-
inder liner.
Piston ring sticking
Replace the related parts
Valve spring
Valve spring weak or broken
Replace the valve spring
Checkpoint
Possible cause
Correction
Engine oil
Engine oil unsuitable
Too much engine oil
Replace the engine oil
Correct the engine oil level
Oil seal and gasket
Oil leakage from the oil seal and/or the
gasket
Replace the oil seal and/or the gasket
Air breather
Clogged air breather
Clean the air breather
Intake and exhaust
valve
Worn valve stems and valve guides
Replace the intake and exhaust valves
and the valve guides
Checkpoint
Possible cause
Correction
Cooling water
Insufficient cooling water
Replenish the cooling water
Fan clutch
Oil leakage from the fan clutch
Replace the fan clutch
Fan belt
Fan belt loose or cracked causing slippage Replace the fan belt
Radiator
Defective radiator cap or clogged radiator
core
Replace the radiator cap or clean the radi-
ator core
Water pump
Defective water pump
Repair or replace the water pump
Cylinder head and cyl-
inder body sealing cap
Defective sealing cap resulting in water
leakage
Replace the sealing cap
Thermostat
Defective thermostat
Replace the thermostat
Cooling system
Cooling system clogged by foreign mate-
rial
Clean the foreign material from the cooling
system
Fuel injection timing
Fuel injection timing improperly adjusted
Adjust the fuel injection timing
00-8 SERVICE INFORMATION
White Exhaust Smoke
Dark Exhaust Smoke
Oil Pressure Does Not Rise
Checkpoint
Possible cause
Correction
Cooling water
Insufficient cooling water
Replace the cooling water
Fuel
Water particles in the fuel
Replace the fuel
Fuel injection timing
Delayed fuel injection timing
Adjust the fuel injection timing
Compression pressure
Blown out cylinder head gasket. Worn cyl-
inder liner.
Piston ring sticking
Replace the related parts
Inlet and exhaust valve
Valves seals
Defective valve seals.
Worn valves stems and valve guides
Replace the valve seals, the valves, and
the valve guides
Checkpoint
Possible cause
Correction
Air cleaner
Clogged air cleaner element
Clean or replace the air cleaner element
Injection nozzle
Injection nozzle injection starting pressure
too low
Improper spray condition
Adjust or replace the injection nozzle
Fuel injection timing
Fuel injection timing improperly adjusted
Adjust the fuel injection timing
Injection pump
Defective delivery valve resulting in fuel
drippage after fuel injection
Replace the delivery valve
Excessive injection volume
Adjust the injection volume
Checkpoint
Possible cause
Correction
Engine oil
Improper viscosity engine oil.
Insufficient engine oil
Replace the engine oil
Correct the engine oil volume
Oil pressure gauge or
unit
Defective oil pressure gauge or unit
Repair or replace the oil pressure gauge or
unit
Oil pressure indicator
light
Defective indicator light
Replace the indicator light
Oil filter
Clogged oil filter element
Replace the oil filter element or the oil filter
cartridge
Relief valve and by-
pass valve
Relief valve sticking and/or weak by-pass
valve spring
Replace the relief valve and/or the by-pass
valve spring
Oil pump
Clogged oil pump strainer
Clean the oil pump strainer
Worn oil pump related parts
Replace the oil pump related parts
Rocker arm shaft
Worn rocker arm bushing
Replace the rocker arm bushing
Camshaft
Worn camshaft and camshaft bearing
Replace the camshaft and the camshaft
bearing
Crankshaft and bear-
ings
Worn crankshaft and bearings
Replace the crankshaft and/or the bear-
ings
SERVICE INFORMATION 00-9
Abnormal Engine Noise
1. Engine Knocking
Check to see that the engine has been thoroughly warmed up before beginning the troubleshooting procedure.
2. Gas Leakage Noise
3. Continuous Noise
4. Slapping Noise
Checkpoint
Possible cause
Correction
Fuel
Fuel unsuitable
Replace the fuel
Fuel injection timing
Fuel injection timing improperly adjusted
Adjust the fuel injection timing
Injection nozzle
Improper injection nozzle starting pressure
and spray condition
Adjust or replace the injection nozzle
Compression pressure
Blown out head gasket
Broken piston ring
Replace the head gasket or the piston ring
Checkpoint
Possible cause
Correction
Exhaust pipes
Loosely connected exhaust pipes. Broken
exhaust pipes
Tighten the exhaust pipe connections
Replace the exhaust pipes
Injection nozzles and/
or glow plugs
Loose injection nozzles and/or glow plugs
Replace the washers
Tighten the injection nozzles and/or the
glow plugs
Exhaust manifold
Loosely connected exhaust manifold and/
or glow plugs
Tighten the exhaust manifold connections
Cylinder head gasket
Damaged cylinder head gasket
Replace the cylinder head gasket
Checkpoint
Possible cause
Correction
Fan belt
Loose fan belt
Readjust the fan belt tension
Cooling fan
Loose cooling fan
Retighten the cooling fan
Water pump bearing
Worn or damaged water pump bearing
Replace the water pump bearing
Generator or vacuum
pump
Defective generator or vacuum pump
Defective generator or vacuum pump
Repair or replace the generator or the vac-
uum pump
Valve clearance
Clearance improperly adjust
Adjust the valve clearances
Checkpoint
Possible cause
Correction
Valve clearance
Valve clearance improperly adjusted
Adjust the valve clearance
Rocker arm
Damaged rocker arm
Replace the rocker arm
Flywheel
Loose flywheel bolts
Retighten the flywheel bolts
Crankshaft and thrust
bearings
Worn or damaged crankshaft and/or thrust
bearings
Replace the crankshaft and/or the thrust
bearings
Crankshaft and con-
necting rod bearings
Worn or damaged crankshaft and/or con-
necting rod bearings
Replace the crankshaft and/or the con-
necting rod bearings
Connecting rod bush-
ing and piston pin
Worn or damaged connecting rod bushing
and piston pin
Replace the connecting rod bushing and/
or the piston pin
Piston and cylinder
liner
Worn or damaged piston and cylinder
liner.
Replace the piston and the cylinder liner.
00-10 SERVICE INFORMATION
Engine Cooling Trouble
Checkpoint
Possible cause
Correction
Engine overheating
Low coolant level
Replenish
Thermo unit faulty
Replace
Faulty thermostat
Replace
Faulty coolant unit
Repair or replace
Clogged radiator
Clean or replace
Faulty radiator cap
Replace
Low engine oil level or use of improper
engine oil
Replenish or change oil
Replenish
Damaged cylinder head gasket
Replace
Clogged exhaust system
Clean exhaust system or replace faulty
parts
Loose fan belt
Adjust
Excessive fuel injected
Adjust
Improper injection timing
Adjust
Engine overcooling
Faulty thermostat
Replace
Too long engine warm-
up time
Faulty thermostat
Replace
Thermo unit faulty
Replace
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