1998 ISUZU TROOPER fuel pressure

6E±349 ENGINE DRIVEABILITY AND EMISSIONS

Damage during re-gapping can happen if the gapping
tool is pushed against the center electrode or the
insulator around it, causing the insulator to crack.
When re-gapping a spark plug, make the adjustment
by bending only the ground side terminal, keeping the
tool clear of other parts.

ºHeat shockº breakage in the lower insulator tip
generally occurs during several engine operating
conditions (high speeds or heavy loading) and may be
caused by over-advanced timing or low grade fuels.
Heat shock refers to a rapid increase in the tip
temperature that causes the insulator material to
crack.
Spark plugs with less than the recommended amount of
service can sometimes be cleaned and re-gapped , then
returned to service. However, if there is any doubt about
the serviceability of a spark plug, replace it. Spark plugs
with cracked or broken insulators should always be
replaced.
A/C Clutch Diagnosis
A/C Clutch Circuit Operation
A 12-volt signal is supplied to the A/C request input of the
PCM when the A/C is selected through the A/C control
switch.
The A/C compressor clutch relay is controlled through the
PCM. This allows the PCM to modify the idle air control
position prior to the A/C clutch engagement for better idle
quality. If the engine operating conditions are within their
specified calibrated acceptable ranges, the PCM will
enable the A/C compressor relay. This is done by
providing a ground path for the A/C relay coil within the
PCM. When the A/C compressor relay is enabled,
battery voltage is supplied to the compressor clutch coil.
The PCM will enable the A/C compressor clutch
whenever the engine is running and the A/C has been
requested. The PCM will not enable the A/C compressor
clutch if any of the following conditions are met:

The throttle is greater than 90%.

The engine speed is greater than 6315 RPM.

The ECT is greater than 119
C (246
F).

The IAT is less than 5
C (41
F).

The throttle is more than 80% open.
A/C Clutch Circuit Purpose
The A/C compressor operation is controlled by the
powertrain control module (PCM) for the following
reasons:

It improvises idle quality during compressor clutch
engagement.

It improvises wide open throttle (WOT) performance.

It provides A/C compressor protection from operation
with incorrect refrigerant pressures.
The A/C electrical system consists of the following
components:

The A/C control head.

The A/C refrigerant pressure switches.

The A/C compressor clutch.

The A/C compressor clutch relay.
The PCM.
A/C Request Signal
This signal tells the PCM when the A/C mode is selected
at the A/C control head. The PCM uses this to adjust the
idle speed before turning on the A/C clutch. The A/C
compressor will be inoperative if this signal is not
available to the PCM.
Refer to
A/C Clutch Circuit Diagnosis for A/C wiring
diagrams and diagnosis for A/C electrical system.
General Description (Exhaust Gas
Recirculation (EGR) System)
EGR Purpose
The exhaust gas recirculation (EGR) system is use to
reduce emission levels of oxides of nitrogen (NOx). NOx
emission levels are caused by a high combustion
temperature. The EGR system lowers the NOx emission
levels by decreasing the combustion temperature.
057RW002
Linear EGR Valve
The main element of the system is the linear EGR valve.
The EGR valve feeds small amounts of exhaust gas back
into the combustion chamber. The fuel/air mixture will be
diluted and combustion temperatures reduced.
Linear EGR Control
The PCM monitors the EGR actual positron and adjusts
the pintle position accordingly. The uses information from
the following sensors to control the pintle position:

Engine coolant temperature (ECT) sensor.

Throttle position (TP) sensor.

Mass air flow (MAF) sensor.
Linear EGR Valve Operation and Results
of Incorrect Operation
The linear EGR valve is designed to accurately supply
EGR to the engine independent of intake manifold
vacuum. The valve controls EGR flow from the exhaust

6E±350
ENGINE DRIVEABILITY AND EMISSIONS
to the intake manifold through an orifice with a PCM
controlled pintle. During operation, the PCM controls
pintle position by monitoring the pintle position feedback
signal. The feedback signal can be monitored with Tech 2
as ªActual EGR Pos.º ªActual EGR Pos.º should always
be near the commanded EGR position (ºDesired EGR
Pos.º). If a problem with the EGR system will not allow the
PCM to control the pintle position properly, DTC P1406
will set. The PCM also tests for EGR flow. If incorrect flow
is detected, DTC P0401 will set. If DTCs P0401 and/or
P1406 are set, refer to the DTC charts.
The linear EGR valve is usually activated under the
following conditions:

Warm engine operation.

Above-idle speed.
Too much EGR flow at idle, cruise or cold operation may
cause any of the following conditions to occur:

Engine stalls after a cold start.

Engine stalls at idle after deceleration.

Vehicle surges during cruise.

Rough idle.
Too little or no EGR flow may allow combustion
temperatures to get too high. This could cause:

Spark knock (detonation).

Engine overheating.

Emission test failure.

DTC P0401 (EGR flow test).

Poor fuel economy.
0017
EGR Pintle Position Sensor
The PCM monitors the EGR valve pintle position input to
endure that the valve responds properly to commands
from the PCM and to detect a fault if the pintle position
sensor and control circuits are open or shorted. If the
PCM detects a pintle position signal voltage outside the
normal range of the pintle position sensor, or a signal
voltage that is not within a tolerance considered
acceptable for proper EGR system operation, the PCM
will set DTC P1406.
General Description (Positive
Crankcase Ventilation (PCV) System)
Crankcase Ventilation System Purpose
The crankcase ventilation system is use to consume
crankcase vapors in the combustion process instead of
venting them to the atmosphere. Fresh air from the
throttle body is supplied to the crankcase and mixed with
blow-by gases. This mixture is then passed through the
positive crankcase ventilation (PCV) valve into the
common chamber.
Crankcase Ventilation System Operation
The primary control is through the positive crankcase
ventilation (PCV) valve. The PCV valve meters the flow at
a rate that depends on the intake vacuum. The PCV valve
restricts the flow when the inlet vacuum is highest. In
addition, the PCV valve can seal the common chamber
off in case of sudden high pressure in the crankcase.
028RV002
While the engine is running, exhaust fuses and small
amounts of the fuel/air mixture escape past the piston

00 Ð 2 SERVICE INFORMATION
TROUBLESHOOTING
CONTENTS
PAGE
Hard Starting ................................................................................................................... 00- 3
Starter Motor Inoperative ........................................................................................... 00- 3
Starter Motor Operates but Engine does not turn over ........................................... 00- 3
Engine turns over but does not start ......................................................................... 00- 4
Quick-on Start System (QOS III) ................................................................................. 00- 5
Unstable Idling ................................................................................................................. 00- 5
Insufficient Power ............................................................................................................ 00- 7
Excessive Fuel Consumption .......................................................................................... 00- 9
Excessive Oil Consumption ............................................................................................. 00- 9
Overheating ...................................................................................................................... 00-10
White Exhaust Smoke ..................................................................................................... 00-10
Dark Exhaust Smoke ........................................................................................................ 00-11
Oil Pressure Does Not Rise .............................................................................................. 00-11
Abnormal Engine Noise ................................................................................................... 00-12
Engine Knocking .......................................................................................................... 00-12
Gas Leakage noise ....................................................................................................... 00-12
Continuous noise ......................................................................................................... 00-12
Slapping noise .............................................................................................................. 00-13
Engine Cooling Trouble ................................................................................................... 00-14
Engine Electrical ............................................................................................................... 00-15
Starter does not run .................................................................................................... 00-15
Faulty Meshing or Pinion and Ring Gear ................................................................... 00-16
Magnetic Switch does not operate though starter switch is turned to ÒStart (ST)Ó ...00-17
Pinion Meshes with ring gear but engine does not run ........................................... 00-18
Starter does not stop though starter switch is returned to ÒONÓ .......................... 00-19

00 Ð 4 SERVICE INFORMATION
Checkpoint Possible cause Correction
Engine stop
mechanismDefective fuel cut solenoid valve Replace the fuel cut solenoid valve
3. ENGINE TURNS OVER BUT DOES NOT START
FUEL IS NOT BEING DELIVERED TO THE INJECTION PUMP
Fuel Fuel tank is empty Fill the fuel tank
Fuel piping Clogged or damaged fuel lines. Loose fuel
line connectionRepair or replace the fuel lines
Retighten the fuel line connection
Fuel filter Fuel filter overflow valve does not close Repair or replace the fuel filter
overflow valve
Clogged fuel filter element Replace the fuel filter element or
the filter cartridge
Fuel system Air in the fuel system Bleed the air from the fuel system
Fuel feed pump Defective feed pump Repair or replace the feed pump
FUEL IS BEING DELIVERED TO THE INJECTION PUMP
Fuel Use of the wrong fuel Use the correct fuel
Water particles in the fuel Carge the fuel
Fuel system Air in the injection pump Bleed the air from the fuel system
Injection nozzle Injection nozzle sticking Replace the injection nozzle
Injection nozzle injection starting pressure
too low
Improper spray conditionAdjust or replace the injection
nozzle
Injection pump Defective fuel injection nozzle resulting in
the fuel drippage after fuel injectionReplace the delivery valve
Defective injection pump control rack
operationRepair or replace the injection pump
control rack
Injection pump plunger worn or stuck Replace the injection pump plunger
assembley
Injection pump drive shaft seizure or other
damageReplace the injection drive shaft
Injection pump governor spring seizure Replace the injection pump
governor spring

00 Ð 6 SERVICE INFORMATION
Checkpoint Possible cause Correction
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 improperly adjusted Adjust the valve clearance Valve clearance
Blown out cylinder head gasket. Worn
cylinder liner.
Piston ring sticking between
the valve and the valve seatReplace the related parts Compression
pressure
Fuel system leakage or blockage Repair or replace the fuel system Fuel system
Air in the fuel system Bleed the air from the fuel system
Water particles in the fuel system Change the fuel
Clogged fuel filter element Replace the fuel filter element or
the fuel filter cartridge Fuel filter
Defective fuel feed pump Repair or replace the fuel feed pump Fuel feed pump
Injection nozzle sticking Replace the injection nozzle Injection nozzle
Injection nozzle injection starting pressure
too low
Improper spray conditionAdjust or replace the injection
nozzle
Defective delivery valve resulting in fuel
drippage after fuel injectionReplace the delivery valve Injection pump

SERVICE INFORMATION 00 Ð 7
3. INSUFFICIENT POWER
Clogged air cleaner element Clean or replace the air cleaner
element Air cleaner
Checkpoint Possible cause Correction
Water particle in the fuel Replace fuel Fuel
Clogged fuel filter element Replace the fuel filter element or
the fuel filter cartridge Fuel filter
Defective fuel feed pump Repair or replace the fuel feed pump Fuel feed pump
Injection nozzle sticking Replace the injection nozzle Injection nozzle
Injection nozzle injection starting pressure
too low
Improper spray conditionAdjust or replace the injectionn
nozzle
Fuel injection pipes damaged or obstructed Replace the fuel injection pipes Fuel injection pipes
Defective regulating valve Repair or replace the regulating
valve Injection pump
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 saaembly
Worn cam disk Replace the cam disk

SERVICE INFORMATION 00 Ð 9
4. EXCESSIVE FUEL CONSUMPTION
5. EXCESSIVE OIL CONSUMPTION
Checkpoint Possible cause Correction
Engine oil Engine oil unsuitable
Too mauch engine oilReplace the engine oil
Correct the engine oil level
Oil seal and gasket Oil leakage from the oilseal and/or the
gasketReplace the oil seal and/or the
gasket
Air breather Clogged air breather Clean the air breather
Intake and exhaust
valveWorn valve stems and valve guides Replace the intake and exhaust
valves and the valve springs
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 injectionReplace the delivery valve
Turbocharger Air leakage from the turbocharger intake
sideRepair the turbocharger intake side
Defective turbocharger assembly Replace the turbocharger assembly
Valve clearance Valve clearance improperly adjusted Adjust the valve clearance
Compression
pressureBlown out cylinder head gasket. Worn
cylinder liner.
Piston ring sticking between the valve and
valve seatReplace the related parts
Valve spring Valve spring weak or broken Replace the valve spring

00 Ð 10 SERVICE INFORMATION
6. OVERHEATING
7. WHITE EXHAUST SMOKE
Checkpoint 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
pressureBlown out cylinder head gasket. Worn
cylinder liner.
Piston ring sticking between the valve and
valve seatReplace the related parts
Turbocharger Defective turbocharger Replace the turbocharger
Inlet and exhaust
valves
Valves sealsDefective valve seales.
Worn valves stems and valve guidesReplace the valve seales, the valves,
and the valve guides
Checkpoint Possible cause Correction
Cooling water Insufficient cooling water Replace 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
coreReplace the radiator cap or clean the
radiator core
Water pump Defective water pump Repair or replace the water pump
Cylinder head and
cylinder body sealing
capDefective searing cap resulting in water
leakageReplace the sealing cap
Thermostat Defective thermostat Replace the thermostat
Cooling system Cooling system clogged by foreign
materialClean the foreign material from the
cooling system
Fuel injection timing Fuel injection timing improperly adjusted Adjust the fuel injection timing