1998 ISUZU TROOPER Remove engine

6E±82
ENGINE DRIVEABILITY AND EMISSIONS
Engine Cranks But Will Not Run

 
StepNo Ye s Value(s) Action
131. Remove any ignition coil and install a spark tester at
the spark plug end of the coil.
2. Observe the tester while the engine is cranking.
Was a crisp, blue spark observed? Only one or two
sparks followed by no result is considered the same as
ªNo Spark.º
ÐGo to Step 15Go to Step 14
14Replace the ignition coil, and return to Step 13 to test
the remaining coils.
Is the action complete?
ÐVerify repairÐ
15Repeat Step 13 for each coil. Remove only one coil at a
time, and reinstall each coil on its spark plug after
testing, but do not refasten coils with screws at this
time.
After all coils have passed the spark test, does the
engine start?
Ð
Refasten all
coils with
their screws
Go to Step 16
161. Remove the spark plugs from all cylinders.
2. Visually inspect the spark plug electrodes.
3. Replace any spark plugs with loose or missing
electrodes or cracked insulators.
Did your inspection reveal any spark plugs exhibiting
excessive fouling?
Ð
Correct the
fouling
condition
Go to Step 17
17Refer to Engine Mechanical Diagnosis to diagnose the
following conditions:

Faulty or incorrect camshaft drive belts

Leaking or sticky valves or rings

Excessive valve deposits

Loose or worn rocker arms

Weak valve springs

Incorrect valve timing

Leaking head gasket
Is the action complete?
ÐVerify repairGo to Step 19
18Observe the ªEngine Speedº data display on the scan
tool while cranking the engine.
Is the engine RPM indicated? (If the scan tool is
normally powered from the cigarette lighter socket, and
if the scan tool display goes blank while cranking the
engine, it will be necessary to power the scan tool
directly from the vehicle battery.)
ÐGo to Step 19Go to Step 28
191. Disconnect the 7-pin gray connector at the rear of
the air filter beneath the point where the air duct
attaches to the MAF sensor.
2. Ignition ªON.º
3. Using a test light connected to ground, probe the
ignition terminal at the PCM (female) side of the
7-pin connector.
Is the test light ªON?º
ÐGo to Step 20Go to Step 26

6E±86
ENGINE DRIVEABILITY AND EMISSIONS
CAUTION: To reduce the risk of fire and personal
injury:

It is necessary to relieve fuel system pressure
before connecting a fuel pressure gauge. Refer to
Fuel Pressure Relief Procedure, below.

A small amount of fuel may be released when
disconnecting the fuel lines. Cover fuel line
fittings with a shop towel before disconnecting, to
catch any fuel that may leak out. Place the towel in
an approved container when the disconnect is
completed.Fuel Pressure Relief Procedure
1. Remove the fuel cap.
2. Remove the fuel pump relay from the underhood
relay center.
3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.
Fuel Gauge Installation
1. Remove the shoulder fitting cap.
2. Install fuel gauge 5-8840-0378-0 to the fuel feed line
located in front of and above the right side valve train
cover .
3. Reinstall the fuel pump relay.
Fuel System Electrical Test

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Read the ªCautionº above.
2. Relieve the fuel system pressure and install the fuel
pump pressure gauge to the test fitting.
3. Use Tech 2 to command the fuel pump ªON.º
Is there an immediate pressure build-up which
indicates the pump is running?
ÐGo to Step 3Go to Step 4
31. Verify that the pump is not running by removing the
fuel filler cap and listening.
2. Command the pump ªONº with Tech 2.
Did the pump turn ªOFFº after 2 seconds?
Ð
Test
completed
Go to Step 12
41. Ignition ªOFF.º
2. Remove the fuel pump relay.
3. Using a test light connected to ground, probe the
battery feed to the relay.
Did the light illuminate?
ÐGo to Step 6Go to Step 5
5Repair short or open battery feed to fuel pump relay.
Is the action complete?
ÐVerify repairÐ
61. Connect a test light between the two wires that
connect to the fuel pump relay pull-in coil.
2. Ignition ªON.º
Did the test light illuminate for 2 seconds and then turn
off?
ÐGo to Step 12Go to Step 7
71. With a test light connected to battery (±), probe the
fuel pump relay connector at the wire which runs
from the relay pull-in coil to the PCM.
2. Ignition ªON.º
Did the test light illuminate for 2 seconds and then turn
off?
ÐGo to Step 8Go to Step 9
8Locate and repair open in the fuel pump relay ground
circuit.
Is the action complete?
ÐVerify repairÐ

6E±89 ENGINE DRIVEABILITY AND EMISSIONS

The valve or valve seat within the fuel pressure
regulator.

The fuel injector(s).
4. Fuel pressure that drops off during acceleration,
cruise, or hard cornering may case a lean condition.
A lean condition can cause a loss of power, surging,
or misfire. A lean condition can be diagnosed using
a Tech II Tech 2. If an extremely lean condition
occurs, the oxygen sensor(s) will stop toggling. The
oxygen sensor output voltage(s) will drop below 500
mV. Also, the fuel injector pulse width will increase.
IMPORTANT:Make sure the fuel system is not
operating in the ªFuel Cut-Off Mode.º
When the engine is at idle, the manifold pressure is
low (high vacuum). This low pressure (high vacuum)
is applied to the fuel pressure regulator diaphragm.
The low pressure (high vacuum) will offset the
pressure being applied to the fuel pressure regulator
diaphragm by the spring inside the fuel pressure
regulator. When this happens, the result is lower fuel
pressure. The fuel pressure at idle will vary slightly as
the barometric pressure changes, but the fuel
pressure at idle should always be less than the fuel
pressure noted in step 2 with the engine ªOFF.º
16.Check the spark plug associated with a particular
fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking. If
checking the spark plug associated with a particular
fuel injector for fouling or saturation does not
determine that a particular fuel injector is leaking,
use the following procedure:

Remove the fuel rail, but leave the fuel lines and
injectors connected to the fuel rail. Refer to
Fuel Rail
Assembly
in On-Vehicle Service.

Lift the fuel rail just enough to leave the fuel injector
nozzles in the fuel injector ports.
CAUTION: In order to reduce the risk of fire and
personal injury that may result from fuel spraying on
the engine, verify that the fuel rail is positioned over
the fuel injector ports and verify that the fuel injector
retaining clips are intact.

Pressurize the fuel system by connecting a 10 amp
fused jumper between B+ and the fuel pump relay
connector.

Visually and physically inspect the fuel injector
nozzles for leaks.
17.A rich condition may result from the fuel pressure
being above 376 kPa (55 psi). A rich condition may
cause a DTC P0132 or a DTC P0172 to set.
Driveability conditions associated with rich
conditions can include hard starting (followed by
black smoke) and a strong sulfur smell in the
exhaust.20.This test determines if the high fuel pressure is due
to a restricted fuel return line or if the high fuel
pressure is due to a faulty fuel pressure regulator.
21.A lean condition may result from fuel pressure
below 333 kPa (48 psi). A lean condition may
cause a DTC P0131 or a DTC P0171 to set.
Driveability conditions associated with lean
conditions can include hard starting (when the
engine is cold ), hesitation, poor driveability, lack of
power, surging , and misfiring.
22.Restricting the fuel return line causes the fuel
pressure to rise above the regulated fuel pressure.
Command the fuel pump ªONº with Tech 2. The fuel
pressure should rise above 376 kPa (55 psi) as the
fuel return line becomes partially closed.
NOTE: Do not allow the fuel pressure to exceed 414 kPa
(60 psi). Fuel pressure in excess of 414 kPa (60 psi) may
damage the fuel pressure regulator.
CAUTION: To reduce the risk of fire and personal
injury:

It is necessary to relieve fuel system pressure
before connecting a fuel pressure gauge. Refer to
Fuel Pressure Relief Procedure, below.

A small amount of fuel may be released when
disconnecting the fuel lines. Cover fuel line
fittings with a shop towel before disconnecting, to
catch any fuel that may leak out. Place the towel in
an approved container when the disconnect is
completed.
Fuel Pressure Relief Procedure
1. Remove the fuel cap.
2. Remove the fuel pump relay from the underhood
relay center.
3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.
Fuel Gauge Installation
1. Remove the shoulder fitting cap.
2. Install fuel gauge 5-8840-0378-0 to the fuel feed line
located in front of and above the right side valve train
cover.
3. Reinstall the fuel pump relay.

6E±90
ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis

StepActionValue(s)Ye sNo
1Was the ªOn-Board Diagnostic (OBD) System Checkº
performed?
ÐGo to Step 2
Go to OBD
System
Check
21. Turn the ignition ªOFF.º
2. Turn the air conditioning system ªOFF.º
3. Relieve fuel system pressure and install the fuel
pressure gauge.
4. Turn the ignition ªON.º
NOTE: The fuel pump will run for approximately 2
seconds. Use Tech 2 to command the fuel pump ªONº.
5. Observe the fuel pressure indicated by the fuel
pressure gauge with the fuel pump running.
Is the fuel pressure within the specified limits?
290-376 kPa
(42-55 psi)
Go to Step 3Go to Step 17
3NOTE: The fuel pressure will drop when the fuel pump
stops running, then it should stabilize and remain
constant.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant?
ÐGo to Step 4Go to Step 12
41. When the vehicle is at normal operation
temperature, turn the ignition ªONº to build fuel
pressure and observe the measurement on the
gauge.
2. Start the engine and observe the fuel pressure
gauge.
Did the reading drop by the amount specified after the
engine was started?
21-105 kPa
(3-15 psi)
Go to Step 5Go to Step 9
5Is fuel pressure dropping off during acceleration,
cruise, or hard cornering?
ÐGo to Step 6
Check for
improper fuel
6Visually and physically inspect the following items for a
restriction:

The in-pipe fuel filter.

The fuel feed line.
Was a restriction found?
ÐVerify repairGo to Step 7
7Remove the fuel tank and visually and physically
inspect the following items:

The fuel pump strainer for a restriction.

The fuel line for a leak.

Verify that the correct fuel pump is in the vehicle.
Was a problem found in any of these areas?
ÐVerify repairGo to Step 8
8Replace the fuel pump.
Is the action complete?
ÐVerify repairÐ
91. Disconnect the vacuum hose from the fuel pressure
regulator.
2. With the engine idling, apply 12-14 inches of
vacuum to the fuel pressure regulator.
Does the fuel pressure indicated by the fuel pressure
gauge drop by the amount specified?
21-105 kPa
(3-15 psi)
Go to Step 10Go to Step 11

6E±91 ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis

 
StepNo Ye s Value(s) Action
10Locate and repair the loss of vacuum to the fuel
pressure regulator.
Is the action complete?
ÐVerify repairÐ
11Replace the fuel pressure regulator.
Is the action complete?
ÐVerify repairÐ
121. Run the fuel pump with Tech 2.
2. After pressure has built up, turn off the pump and
clamp the supply hose shut with suitable locking
pliers.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant?
ÐGo to Step 13Go to Step 15
13Visually inspect the fuel supply line and repair any
leaks.
Was a problem found?
ÐVerify repairGo to Step 14
14Remove the fuel tank and inspect for leaky hose or
in-tank fuel line.
Was a problem found?
ÐVerify repairGo to Step 8
151. If the pliers are still clamped to the fuel supply hose,
remove the locking pliers.
2. With suitable locking pliers, clamp the fuel return
line to prevent fuel from returning to the fuel tank.
3. Run the fuel pump with Tech 2.
4. After pressure has built up, remove power to the
pump.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant?
ÐGo to Step 11Go to Step 16
16Locate and replace any leaking fuel injector(s).
Is the action complete?
ÐVerify repairÐ
17Is the fuel pressure indicated by the fuel pressure
gauge above the specified limit?376 kPa
(55 psi)
Go to Step 18Go to Step 21
181. Relieve the fuel pressure. Refer to the Fuel
Pressure Relief.
2. Disconnect the fuel return line from the fuel rail.
3. Attach a length of flexible hose to the fuel rail return
outlet passage.
4. Place the open end of the flexible hose into an
approved gasoline container.
5. Run the fuel pump with Tech 2.
6. Observe the fuel pressure indicated by the fuel
pressure gauge with the fuel pump running.
Is the fuel pressure within the specified limits?
290-376 kPa
(42-55 psi)
Go to Step 19Go to Step 20
19Locate and correct the restriction in the fuel return line.
Is the action complete?
ÐVerify repairÐ
20Visually and physically inspect the fuel rail outlet
passages for a restriction.
Was a restriction found?
ÐVerify repairGo to Step 11
21Is the fuel pressure indicated by the fuel pressure
gauge above the specified value?
0 kPa (0 psi)Go to Step 22Go to Step 23

6E±92
ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis

 
StepNo Ye s Value(s) Action
221. Command the fuel pump ªONº with Tech 2.
2. Using suitable pliers which will not damage the fuel
hose, gradually apply pressure with the pliers to
pinch the flexible fuel return hose closed.
CAUTION: Do not let the fuel pressure exceed
the second specified value.
Does the fuel pressure indicated by the fuel pressure
gauge rise above the first specified value?
376 kPa
(55 psi)
414 kPa
(60 psi)
Go to Step 11Go to Step 7
231. Command the fuel pump ªONº with Tech 2.
2. Remove the fuel filler cap and listen for the sound of
the fuel pump running.
3. Turn the pump off.
Was the fuel pump running?
ÐGo to Step 7
Go to Fuel
System
Electrical Test
Chart

6E±93 ENGINE DRIVEABILITY AND EMISSIONS
Idle Air Control (IAC) System Check
Circuit Description
The powertrain control module (PCM) controls engine
idle speed with the idle air control (IAC) valve. To increase
idle speed, the PCM retracts the IAC valve pintle away
from its seat, allowing more air to bypass the throttle bore.
To decrease idle speed, it extends the IAC valve pintle
towards its seat, reducing by pass air flow. Tech 2 will
read the PCM commands to the IAC valve in counts.
Higher counts indicate more air bypass (higher idle).
Lower counts indicate less air is allowed to bypass (lower
idle).
Diagnostic Aids
A slow, unstable, or fast idle may be caused by a non-IAC
system problem that cannot be overcome by the IAC
valve. Out of control range IAC Tech 2 counts will be
above 60 if idle is too low, and zero counts if idle is too
high. The following checks should be made to repair a
non-IAC system problem:

Vacuum leak (high idle) ± If idle is too high, stop the
engine. Fully extend (low) IAC with the Tech 2. Start
the engine. If idle speed is above 800 RPM, locate and
correct the vacuum leak, including the PCV system.
Check for binding of the throttle blade or linkage.

Lean heated oxygen sensor signal (high air/fuel ratio) ±
The idle speed may be too high or too low. Engine
speed may vary up and down, and disconnecting the
IAC valve does not help. Diagnostic trouble codes
P0131, P0151, P0171, or P0174 may be set. Tech 2
oxygen (O2) voltage will be less than 100 mV (0.1 V).
Check for low regulated fuel pressure, water in fuel, or
a restricted injector.

Rich heated oxygen sensor signal (low air/fuel ratio) ±
The idle speed will be too low. Tech 2 IAC counts will
usually be above 80. The system is obviously rich and
may exhibit black smoke in the exhaust.
Tech 2 O2 voltage will be fixed at about 750 mV (0.75
V). Check for high fuel pressure, or a leaking or
sticking injector. A silicon-contaminated heated
oxygen sensor will show an O2 voltage slow to
respond on Tech 2.
Throttle body ± Remove the IAC valve and inspect the
bore for foreign material.

IAC valve electrical connections ± IAC valve
connections should be carefully checked for proper
contact.

PCV valve ± An incorrect or faulty PCV valve may
result in an incorrect idle speed. Refer to
Diagnosis,
Rough Idle, Stalling.
If intermittent poor driveability or
idle symptoms are resolved by disconnecting the IAC,
carefully recheck the connections and valve terminal
resistance, or replace the IAC.
Test Description
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
1. The Tech 2 is used to extend and retract the IAC
valve. Valve movement is verified by an engine
speed change. If no change in engine speed
occurs, the valve can be resettled when removed
from the throttle body.
2. This step checks the quality of the IAC movement in
step 1. Between 700 revolutions per minute (RPM)
and about 1500 RPM, the engine speed should
change smoothly with each flash of the tester light
in both extend and retract. If the IAC valve is
retracted beyond the control range (about 1500
RPM), it may take many flashes to extend the IAC
valve before engine speed will begin to drop. This
is normal on certain engines. Fully extending the
IAC may cause engine stall. This may be normal.

6E±98
ENGINE DRIVEABILITY AND EMISSIONS
Exhaust Gas Recirculation (EGR) System Check

StepActionValue(s)Ye sNo
1Check the EGR valve for looseness.
Is the EGR valve Loose?
ÐGo to Step 2Go to Step 3
2Tighten the EGR valve.
Is the action complete?
ÐVerify repairÐ
31. Place the transmission selector in Park or Neutral.
2. Start the engine and idle until warm.
3. Using Tech 2, command EGR ª50% ON.º
Does the engine idle rough and lose RPMs?
Ð
EGR system
working
properly. No
problem
found.
Go to Step 4
41. Engine ªOFF.º
2. Ignition ªON.º
3. Using a test light to ground, check the EGR harness
between the EGR valve and the ignition feed.
Does the test light illuminate?
ÐGo to Step 6Go to Step 5
5Repair the EGR harness ignition feed.
Was the problem corrected?
ÐVerify repairGo to Step 6
61. Remove the EGR valve.
2. Visually and physically inspect the EGR valve
pintle, valve passages and adapter for excessive
deposits, obstructions or any restrictions.
Does the EGR valve have excessive deposits,
obstructions or any restrictions?
ÐGo to Step 7Go to Step 8
7Clean or replace EGR system components as
necessary.
Was the problem corrected?
ÐVerify repairGo to Step 8
81. Ground the EGR valve metal case to battery (±).
2. Using Tech 2, command EGR ªONº and observe the
EGR valve pintle for movement.
Does the EGR valve pintle move according to
command?
ÐGo to Step 9
Go to DTC
P1406 chart
91. Remove the EGR inlet and outlet pipes from the
intake and exhaust manifolds.
2. Visually and physically inspect manifold EGR ports
and EGR inlet and outlet pipes for blockage or
restriction caused by excessive deposits or other
damage.
Do the manifold EGR ports or inlet and outlet pipes
have excessive deposits, obstructions, or any
restrictions?
ÐGo to Step 10
EGR system
working
properly. No
problem
found.
10Clean or replace EGR system components as
necessary.
Is the action complete?
ÐVerify repairÐ