Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual — part 215
ENGINE DRIVEABILITY AND EMISSIONS
6E–101
• 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 2 Scan Tool.
Following are applicable to the vehicle with
closed Loop System:
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 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 OFF.
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 20
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 45 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 44 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 ON with the scan tool. 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. Located on the intake manifold which is at the top
right part of the engine.
3. Start the engine and allow it to stall.
4. Crank the engine for an additional 3 seconds.
Fuel Pressure Gauge Installation
1. Remove the fuel pressure fitting cap.
2. Install fuel pressure gauge 5-8840-0378-0 to the
fuel feed line located on the upper right side of the
engine.
3. Reinstall the fuel pump relay.
6E–102
ENGINE DRIVEABILITY AND EMISSIONS
Fuel System Diagnosis
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 ignition OFF.
2. Turn the air conditioning system OFF.
3. Relieve fuel system pressure and install the fuel
pressure gauge.
4. Turn the ignition ON.
NOTE: The fuel pump will run for approximately 2
seconds. Use the Scan Tool to command the fuel
pump ON.
5. Observe the fuel pressure indicated by the fuel
pressure gauge with the fuel pump running.
Is the fuel pressure within the specified limits?
283-376 kPa
(41-55 psi)
Go to Step 3
Go to Step 17
3
Does the fuel pressure indicated by the fuel pressure
gauge remain constant?
NOTE: The fuel pressure will drop when the fuel
pump stops running, then it should stabilize and
remain constant.
—
Go to Step 4
Go to Step 12
4
1. When the vehicle is at normal operating
temperature, turn the ignition ON 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 5
Go to Step 9
5
Is fuel pressure dropping off during acceleration,
cruise, or hard cornering?
—
Go to Step 6
Check for
improper fuel
6
Visually and physically inspect the following items for
a restriction:
• The in-line fuel filter.
• The fuel feed line.
Was a restriction found?
—
Verify repair
Go to Step 7
7
Remove 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?
—
Verify repair
Go to Step 8
8
Replace the fuel pump.
Is the action complete?
—
Verify repair
—
9
1. 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 10
Go to Step 11
ENGINE DRIVEABILITY AND EMISSIONS
6E–103
10
Locate and repair the loss of vacuum to the fuel
pressure regulator.
Is the action complete?
—
Verify repair
—
11
Replace the fuel pressure regulator.
Is the action complete?
—
Verify repair
—
12
1. Run the fuel pump with the Scan Tool.
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?
—
Go to Step 13
Go to Step 15
13
Visually inspect the fuel supply line and repair any
leaks.
Was a problem found?
—
Verify repair
Go to Step 14
14
Remove the fuel tank and inspect for leaky hose or in-
tank fuel line.
Was a problem found?
—
Verify repair
Go to Step 8
15
1. 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 the Scan Tool.
4. After pressure has built up, remove power to the
pump.
Does the fuel pressure indicated by the fuel pressure
gauge remain constant?
—
Go to Step 11
Go to Step 16
16
Locate and replace any leaking fuel injector(s).
Is the action complete?
—
Verify repair
—
17
Is the fuel pressure indicated by the fuel pressure
gauge above the specified limit?
376 kPa
(55 psi)
Go to Step 18
Go to Step 21
18
1. 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 the Scan Tool.
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 19
Go to Step 20
19
Locate and correct the restriction in the fuel return
line.
Is the action complete?
—
Verify repair
—
20
Visually and physically inspect the fuel rail outlet
passages for a restriction.
Was a restriction found?
—
Verify repair
Go to Step 11
21
Is the fuel pressure indicated by the fuel pressure
gauge above the specified value?
0 kPa (0 psi)
Go to Step 22
Go to Step 23
Step
Action
Value(s)
Yes
No
6E–104
ENGINE DRIVEABILITY AND EMISSIONS
22
1. Command the fuel pump ON with the Scan Tool.
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.
376 kPa
(55 psi)
Does the fuel pressure indicated by the fuel pressure
gauge rise above the first specified value?
Caution: Do not let the fuel pressure exceed the
second specified value.
414 kPa
(60 psi)
Go to Step 11
Go to Step 7
23
1. Command the fuel pump ON with the Scan Tool.
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?
—
Go to Step 7
Go to Fuel
System
Electrical Test
Chart
Step
Action
Value(s)
Yes
No
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