Isuzu KB P190. Manual - part 569

6E–106

ENGINE DRIVEABILITY AND EMISSIONS

10

Repair the open circuit between the fuel pump relay
and battery. 
Is the action complete?

—

Verify repair

—

11

Using the DVM and check the fuel pump power supply
circuit. 

1. Ignition “On”, engine “Off”. 

2. Disconnect the fuel pump connector. 

3. Check the circuit for open or short to ground

circuit. 

Was the DVM indicated specified value?

10 - 14.5V

Go to Step 13

Go to Step 12

12

Repair the open or short to ground circuit between the
fuel pump relay and fuel pump. 
Is the action complete?

—

Verify repair

—

13

Using the DVM and check the fuel pump ground
circuit. 

1. Ignition “Off”, engine “Off”. 

2. Disconnect the fuel pump connector. 

3. Check the circuit for open circuit. 

Was the DVM indicated specified value?

Continuity

Go to Step 15

Go to Step 14

14

Repair the open circuit between the fuel pump and
body ground. 
Is the action complete?

—

Verify repair

—

15

Replace the fuel pump. 
Was the problem solved?

—

Verify repair

Go to Step 16

16

Is the ECM programmed with the latest software
release? 
If not, download the latest software to the ECM using
the “SPS (Service Programming System)”. 
Was the problem solved?

—

Verify repair

Go to Step 17

Step

Action

Value(s)

Yes

No

V

1

F2

F-2

Ω

4

ENGINE DRIVEABILITY AND EMISSIONS

6E–107

17

Replace the ECM. 
Is the action complete? 
IMPORTANT:  The replacement ECM must be
programmed. Refer to section of the Service
Programming System (SPS) in this manual. 
Following ECM programming, the immobilizer system
(if equipped) must be linked to the ECM. Refer to
section 11 “Immobilizer System-ECM replacement” for
the ECM/Immobilizer linking procedure.

—

Verify repair

—

Step

Action

Value(s)

Yes

No

6E–108

ENGINE DRIVEABILITY AND EMISSIONS

FUEL SYSTEM DIAGNOSIS

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 duel 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 283-376 kPa (41-55 psi). This pressure is
controlled by the amount of 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.

ENGINE DRIVEABILITY AND EMISSIONS

6E–109

• 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.