2004 ISUZU TF SERIES fuel pressure

6E-108 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Injector Coil Test Procedure (Steps 1-6) and Injector Balance Test Procedure
(Steps 7-11)

Step Action Value(s) YES NO
1
Was the “On-Board Diagnostic (OBD) System Check"
performed?
— Go to Step 2 Go to OBD
System Check
2 1. Turn the engine “OFF."
In order to prevent flooding of a single cylinder and
possible engine damage, relieve the fuel pressure
before performing the fuel injector coil test procedure.
2. Relieve the fuel pressure. Refer to Test
Description Number 2.
3. Connect the 5–8840–2618–0 Fuel Injector Tester
to B+ and ground, and to the 5–8840–2635–0
Injector Switch Box.
4. Connect the injector switch box to the gray fuel
injector harness connector located at the rear of
the air cleaner assembly.
5. Set the amperage supply selector switch on the
fuel injector tester to the “Coil Test" 0.5 amp
position.
6. Connect the leads from the Digital Voltmeter
(DVM) to the injector tester. Refer to the
illustrations associated with the test description.
7. Set the DVM to the tenths scale (0.0).
8. Observe the engine coolant temperature.
Is the engine coolant temperature within the specified
values? 10
C (50
F) to
35
C (95
F) Go to Step 3 Go to Step 5
3
1. Set injector switch box injector #1.
2. Press the “Push to Start Test" button on the fuel
injector tester.
3. Observe the voltage reading on the DVM.
Important: The voltage reading may rise during the
test.
4. Record the lowest voltage observed after the first
second of the test.
5. Set the injector switch box to the next injector and
repeat steps 2, 3, and 4.
Did any fuel injector have an erratic voltage reading
(large fluctuations in voltage that did not stabilize) or a
voltage reading outside of the specified values? 5.7-6.6 V Go to Step 4 Go to Step 7
4 Replace the faulty fuel injector(s). Refer to Fuel
Injector.
Is the action complete? — Go to Step 7 —

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-109
Step Action Value(s) YES NO
5
1. Set injector switch box injector #1.
2. Press the “Push to Start Test" button on the fuel
injector tester.
3. Observe the voltage reading on the DVM.
Important: The voltage reading may rise during the
test.
4. Record the lowest voltage observed after the first
second of the test.
5. Set the injector switch box to the next injector and
repeat steps 2, 3, and 4.
Did any fuel injector have an erratic voltage reading
(large fluctuations in voltage that did not stabilize) or a
voltage reading above the specified value? 9.5 V Go to Step 4 Go to Step 6
6
1. Identify the highest voltage reading recorded (other
than those above 9.5 V).
2. Subtract the voltage reading of each injector from
the highest voltage selected in step 1. Repeat until
you have a subtracted value for each injector.
For any injector, is the subtracted Value in step 2
greater than the specified value? 0.6 V Go to Step 4 Go to Step 7
7
CAUTION: In order to reduce the risk of fire and
personal injury, wrap a shop towel around the fuel
pressure connection. The towel will absorb any
fuel leakage that occurs during the connection of
the fuel pressure gauge. Place the towel in an
approved container when the connection of the
fuel pressure gauge is complete.
1. Connect the 5–8840–0378–0 Fuel Pressure Gauge
to the fuel pressure test port.
2. Energize the fuel pump using the Tech 2.
3. Place the bleed hose of the fuel pressure gauge
into an approved gasoline container.
4. Bleed the air out of the fuel pressure gauge.
5. With the fuel pump running, observe the reading
on the fuel pressure gauge.
Is the fuel pressure within the specified values? 296 kPa-376
kPa
(43-55 psi) Go to Step 8 Go to Fuel
System
Diagnosis
8 Turn the fuel pump “OFF."
Does the fuel pressure remain constant?
— Go to Step 9 Go to Fuel
System
Diagnosis

6E-110 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Step Action Value(s) YES NO
9
1. Connect the 5–8840–2618–0 Fuel Injector Tester
and 5–8840–2635–0 Injector Switch Box the fuel
injector harness connector.
2. Set the amperage supply selector switch on the
fuel injector tester to the “Balance Test" 0.5-2.5
amp position.
3. Using the Tech 2 turn the fuel pump “ON" then
“OFF" in order to pressurize the fuel system.
4. Record the fuel pressure indicated by the fuel
pressure gauge after the fuel pressure stabilizes.
This is the first pressure reading.
5. Energize the fuel injector by depressing the “Push
to Start Test" button on the fuel injector tester.
6. Record the fuel pressure indicated by the fuel
pressure gauge after the fuel pressure gauge
needle has stopped moving. This is the second
pressure reading.
7. Repeat steps 1 through 6 for each fuel injector.
8. Subtract the second pressure reading from the first
pressure reading for one fuel injector. The result
is the pressure drop value.
9. Obtain a pressure drop value for each fuel injector.
10. Add all of the individual pressure drop values.
This is the total pressure drop.
11. Divide the total pressure drop by the number of
fuel injectors. This is the average pressure drop.
Does any fuel injector have a pressure drop value that
is either higher than the average pressure drop or
lower than the average pressure drop by the specified
value? 10 kPa
(1.5 psi) Go to Step 10 Go to OBD
System Check
10 Re-test any fuel injector that does not meet the
specification. Refer to the procedure in step 11.
Do not repeat any portion of this test before running
the engine in order to prevent the engine from
flooding.
Does any fuel injector still have a pressure drop value
that is either higher than the average pressure drop or
lower than the average pressure drop by the specified
value? 10 kPa
(1.5 psi) Go to Step 11 Go to
Symptoms
11 Replace the faulty fuel injector(s). Refer to Fuel
Injector.
Is the action complete? — Verify repair —

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-111
FUEL SYSTEM ELECTRICAL TEST




RTW36ELF000101
CIRCUIT DESCRIPTION
When the ignition switch is first turned “ON," the Engine
Control Module (ECM) energizes the fuel pump relay
which applies power to the in-tank fuel pump. The fuel
pump relay will remain “ON" as long as the engine is
running or cranking and the ECM is receiving 58X
crankshaft position pulses. If no 58X crankshaft position
pulses are present, the ECM de-energizes the fuel
pump relay within 2 seconds after the ignition is turned
“ON" or the engine is stopped.
The fuel pump delivers fuel to the fuel rail and injectors,
then to the fuel pressure regulator. The fuel pressure
regulator controls fuel pressure by allowing excess fuel
to be returned to the fuel tank. With the engine stopped
and ignition “ON," the fuel pump can be turned “ON" by
using a command by the Tech 2.
DIAGNOSTIC AIDS
An intermittent may be caused by a poor connection,
rubbed-through wire insulation, or a wire broken inside
the insulation. Check for the following items:
 Poor connection or damaged harness –Inspect the
ECM harness and connectors for improper mating,
broken locks, improperly formed or damaged
terminals, poor terminal-to-wire connection, and
damaged harness.

6E-112 3.5L 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 fuel pressure 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
cover.
3. Reinstall the fuel pump relay.

Fuel System Electrical Test
Step Action Value (s) Yes No
1
Was the "On-Board Diagnostic (OBD) System Check"
performed?
- Go to Step 2 Go to On Board
Diagnostic (OBD)
System Check
2
1. Using the Tech 2, ignition "On" and engine "On".
2. Select the "Miscellaneous Test" and perform the
"Fuel Pump Relay" in the "Relays".
3. Operate the Tech 2 in accordance with procedure.
Was the fuel pump operated, when the Tech 2 is
operated?
- Test completed Go to Step 3
3
Check the "Fuel Pump" fuse (20A). If the fuse is burnt
out, repair as necessary.
Was the problem found?
- Verify repair Go to Step 4
4
Check for poor/faulty connection at the fuel pump, fuel
pump relay or ECM connector. If a poor/faulty
connection is found, repair as necessary.
E-61(B)
X-2


F-2
C-109










Was the problem found?
- Verify repair Go to Step 5

6E-116 3.5L ENGINE DRIVEABILITY AND EMISSIONS
FUEL SYSTEM DIAGNOSIS



RTW36ELF000501
Legend
(1) Fuel Filler Cap
(2) Fuel Tank
(3) Rollover Valve
(4) Fuel Pump Assembly
(5) Fuel Filter
(6) Fuel Rail Right
(7) Intake Air Port Right Bank
(8) Fuel Rail Left
(9) Intake Air Port Left Bank
(10) Fuel Pressure Control Valve
(11) Common Chamber
(12) Duty Solenoid Valve
(13) Throttle Valve
(14) Canister
(15) Check Valve
(16) Air Separator

3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-117
CIRCUIT DESCRIPTION
When the ignition switch is turned “ON," the Engine
Control Module (ECM) will turn “ON" the in-tank fuel
pump. The in-tank fuel pump will remain “ON" as long
as the engine is cranking or running and the ECM is
receiving 58X crankshaft position pulses. If there are no
58X crankshaft position pulses, the ECM will turn the
in-tank fuel pump “OFF" 2 seconds after the ignition
switch is turned “ON" or 2 seconds after the engine
stops running.
The in-tank fuel pump is an electric pump within an
integral reservoir. The in-tank fuel pump supplies fuel
through an in-line fuel filter to the fuel rail assembly. The
fuel pump is designed to provide fuel at a pressure
above the pressure needed by the fuel injectors. A fuel
pressure regulator, attached to the fuel rail, keeps the
fuel available to the fuel injectors at a regulated
pressure. Unused fuel is returned to the fuel tank by a
separate fuel return line.
TEST DESCRIPTION
Number(s) below refer to the step number(s) on the
Diagnostic Chart.
2. Connect the fuel pressure gauge to the fuel feed line
as shown in the fuel system illustration. Wrap a shop
towel around the fuel pressure connection in order to
absorb any fuel leakage that may occur when
installing the fuel pressure gauge. With the ignition
switch “ON" and the fuel pump running, the fuel
pressure indicated by the fuel pressure gauge
should be 333-376 kPa (3.4-3.8 kg/cm
2 / 48-55 psi).
This pressure is controlled by the amount o
f
pressure the spring inside the fuel pressure regulator
can provide.
3. A fuel system that cannot maintain a constant fuel
pressure has a leak in one or more of the following
areas:
 The fuel pump check valve.
 The fuel pump flex line.
 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 1 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 “Fuel Cut-Off Mode."
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 regulato
r
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 “OFF."
16.Check the spark plug associated with a particula
r
fuel injector for fouling or saturation in order to
determine if that particular fuel injector is leaking. I
f
checking the spark plug associated with a particular
fuel injector for fouling or saturation does no
t
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 Fue
l
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 belo
w
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, poo
r
driveability, lack of power, surging , and misfiring.

6E-118 3.5L ENGINE DRIVEABILITY AND EMISSIONS
22.Restricting the fuel return line causes the fuel
pressure to rise above the regulated fuel pressure.
Command the fuel pump “ON" with the 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 fuel pressure fitting cap.
2. Install fuel gauge 5-8840-0378-0 to the fuel supply
line located in front of and above the right side valve
cover.
3. Reinstall the fuel pump relay.