Isuzu N-Series. Manual - part 299

00-8 SERVICE INFORMATION

Unstable Idling

Check point

Possible cause

Correction

Idling system

Idling improperly adjusted

Adjust the idling

Fast idling speed con-
trol device

Defective fast idling speed control device

Repair or replace the fast idling speed 
control device

Accelerator control 
system

Accelerator control system improperly 
adjusted

Adjust the accelerator control system

Fuel system

Fuel system leakage or blockage

Repair or replace the fuel system

Air in the fuel system

Bleed the air from the fuel system

Water particles in the fuel system

Change the fuel

Fuel filter

Clogged fuel filter element

Replace the fuel filter element or the fuel 
filter cartridge

Fuel feed pump

Defective fuel feed pump

Repair or replace the fuel feed pump

Injection nozzle

Injection nozzle sticking

Replace the injection nozzle

Injection nozzle injection starting pressure 
too low
Improper spray condition

Adjust or replace the injection nozzle

Injection pump

Defective delivery valve resulting in fuel 
drippage after fuel injection

Replace the delivery valve

Injection timing improperly adjusted

Adjust the injection timing

Insufficient injection volume

Adjust the injection volume

Defective idle spring

Replace the idle spring

Defective governor lever operation

Repair or replace the governor lever

Regulator valve improperly adjustment

Adjust or replace the regulator valve

Broken plunger spring

Replace the plunger spring

Worn plunger

Replace the plunger assembly

Worn cam disc

Replace the cam disc

Valve clearance

Valve clearance improperly adjusted

Adjust the valve clearance

Compression pressure

Blown out cylinder head gasket
Worn cylinder liner
Piston ring sticking between the valve and 
the valve seat

Replace the related parts

SERVICE INFORMATION 00-9

Insufficient Power

Check point

Possible cause

Correction

Air cleaner

Clogged air cleaner element

Clean or replace the air cleaner element

Fuel

Water particle in the fuel

Replace fuel

Fuel filter

Clogged fuel filter element

Replace the fuel filter element or the fuel 
filter cartridge

Fuel feed pump

Defective fuel feed pump

Repair or replace the fuel feed pump

Injection nozzle

Injection nozzle sticking

Replace the injection nozzle

Injection nozzle injection starting pressure 
too low
Improper spray condition

Adjust or replace the injection nozzle

Fuel injection pipes

Fuel injection pipes damaged or 
obstructed

Replace the fuel injection pipes

Injection pump

Defective regulating valve

Repair or replace the regulating valve

Defective delivery valve

Replace the delivery valve

Defective timer

Repair or replace the timer

Worn cam disk

Replace the cam disk

Improper control lever operation

Adjust or replace the control lever

Defective injection timing

Adjust the injection timing
Repair or replace the injection pump timer

Weak governor spring

Replace the governor spring

Worn plunger

Replace the plunger assembly

Compression pressure

Blown out cylinder head gasket
Worn cylinder liner
Piston ring sticking

Replace the related parts

Valve clearance

Valve clearance improperly adjusted

Adjust the valve clearance

Valve spring

Valve spring weak or broken

Replace the valve spring

Exhaust system

Exhaust pipe clogged

Clean the exhaust pipe

Full load adjusting 
screw seal

Open and improperly set adjusting screw 
seal

Adjust and reseal the adjusting screw

00-10 SERVICE INFORMATION

Excessive Fuel Consumption

Excessive Oil Consumption

Overheating

Check point

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 cylinder liner
Piston ring sticking

Replace the related parts

Valve spring

Valve spring weak or broken

Replace the valve spring

Check point

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

Check point

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

SERVICE INFORMATION 00-11

White Exhaust Smoke

Dark Exhaust Smoke

Oil Pressure Does Not Rise

Check point

Possible cause

Correction

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 cylinder liner
Piston ring sticking

Replace the related parts

Inlet and exhaust 
valves
Valves seals

Defective valve seales
Worn valves stems and valve guides

Replace the valve seales, the valves, and 
the valve guides

Check point

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

Check point

Possible cause

Correction

Engine oil

Improper viscosity engine oil

Replace the engine oil

Insufficient engine oil

Correct the engine oil volume

Oil pressure gauge or 
unit
Oil pressure indicator 
light

Defective oil pressure gauge or unit
Defective indicator light

Repair or replace the oil pressure gauge or 
unit
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