Isuzu N-Series. 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