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Isuzu N-Series. Manual - part 760

Engine Control System (4JH1) 6E-91

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine and let idle for 30 seconds.

Monitor the Diagnostic Trouble Code (DTC)
Information with the Tech 2.

Is DTC P0335 (Symptom Code B or D), P1335
(Symptom Code A) or P1345 (Symptom Code A)
set?

—

Go to Applicable

DTC

Go to Step 3

Turn OFF the engine.

Place the transmission in neutral and set the
park brake.

Start the engine and let engine idle for 30
seconds while observing the Actual Injection
Timing parameter with the Tech 2.

Accelerate the engine and keep the constant
engine speed around 2000 RPM while
observing the Actual Injection Timing
parameter with the Tech 2.

Accelerate the engine and keep the constant
engine speed around 3000 RPM while
observing the Actual Injection Timing
parameter with the Tech 2.

Does the Actual Injection Timing parameter follow
the Desired Injection Timing within 2

°CA on each

engine speed?

—

Go to Diagnostic

Aids

Go to Step 4

Turn OFF the ignition.

Check the fuel system line connections
between the fuel tank and the fuel injection
pump for tightness and all fuel hoses for cuts,
cracks and for the use of proper clamps.

Notice:
The fuel system from the fuel tank(s) to the fuel
injection pump is under a slight vacuum with the
engine running. As a result, air can enter the fuel
system if these connections are not tight. Air in the
fuel system will cause fuel injection pump internal
pressure fluctuations especially at high engine
speed and load, which may set this DTC.

Pump the priming pump on the fuel filter until it
becomes firm. If there is a leak on the suction
side of the fuel system between the priming
pump and the fuel injection pump, the priming
pump will not build up sufficient firmness and
fuel leakage may occur.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 5

Step

Action

Value(s)

Yes

6E-92 Engine Control System (4JH1)

Remove the fuel hose that connects to the fuel
injection pump suction side.

Remove the fuel pipe connector that connects
to the fuel injection pump suction side.

Inspect the eye bolt for any type of restriction
or collapsed gauze filter.

Notice:
If any type of restriction found, check for a condition
that causes contaminated fuel, such as the
customer is using an aftermarket fuel filter or
extended maintenance interval. Also inspect fuel
waxing or icing that is caused by an incorrect fuel
type used in winter season or water intrusion in the
fuel system.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 6

Disconnect the fuel hose that connects to the
fuel injection pump suction side. In order to
measure the discharged fuel amount, put the
hose into a bottle or a container.

Pump the priming pump on the fuel filter.

Notice:
If there is a leak on the suction side of the fuel
system, the fuel from the disconnected hose will
not flow out sufficiently and fuel leakage may occur.
Also if there is a restriction on the suction side of
the fuel system, the fuel from the disconnected
hose will not flow out sufficiently that is most likely
caused by clogged fuel filter or kinked fuel hose or
pipe.

Draw fuel from the fuel tank at the fuel line (as
close to the fuel tank as possible) going to the
fuel pickup tube to verify a clean stream of fuel
comes out (use the hand-held vacuum pump
5-8840-0279-0/J-23738-A with a clear hose or
equivalent). This will ensure the fuel pickup
tube is not cracked drawing air into the fuel
line.

Repair any fuel system leaks and restrictions
as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 7

Step

Action

Value(s)

Yes

Engine Control System (4JH1) 6E-93

Reconnect the fuel pipe connector that
connects to the fuel injection pump suction
side.

Remove the fuel hose that connects to the fuel
injection pump suction side.

Substitute a clear hose.

Notice:
A hose must be cleaned.

Connect the clear hose to the fuel injection
pump.

Bleed the fuel system. Refer to the Diagnostic
Aids.

Let the engine run at idle for at least 2
minutes.

Accelerate the engine between idle and
W.O.T. (accelerator pedal full travel) many
times while observing the clear hose.

Notice:
If many air bubbles appear in the fuel, check the
fuel system line connections between the fuel tank
and the fuel injection pump for tightness and all fuel
hoses for cuts, cracks and for the use of proper
clamps.

Repair as necessary.

Did you find and correct the condition?

—

Go to Step 9

Go to Step 8

Important:
The fuel injection pump must be timed to the
engine.

Replace the fuel injection pump. Refer to Fuel
Injection Pump Replacement in engine mechanical
section.

Did you complete the replacement?

—

Go to Step 9

—

Clear the DTCs with the Tech 2.

Turn OFF the ignition for 30 seconds.

Place the transmission in neutral and set the
park brake.

Start the engine and let engine idle for 30
seconds while observing the Actual Injection
Timing parameter with the Tech 2.

Accelerate the engine and keep the constant
engine speed around 2000 RPM while
observing the Actual Injection Timing
parameter with the Tech 2.

Accelerate the engine and keep the constant
engine speed around 3000 RPM while
observing the Actual Injection Timing
parameter with the Tech 2.

Does the Actual Injection Timing parameter follow
the Desired Injection Timing within 2

°CA on each

engine speed?

—

Go to Step 10

Go to Step 2

Observe the DTC Information with the Tech 2.

Are there any DTCs that you have not diagnosed?

—

Go to Diagnostic

Trouble Code (DTC)

List

System OK

Step

Action

Value(s)

Yes

6E-94 Engine Control System (4JH1)

P0251 (Symptom Code 6) (Flash Code 53)

Circuit Description
The engine control module (ECM) calculates the
desired fuel injection quantity and timing using data
sent from various sensors. These desired data are
sent to the fuel injection pump control unit (PCU) via a
controller area network (CAN) communication bus.
The PCU also receives signals from the internal inputs:
pump camshaft position (CMP) sensor that is located
inside the fuel injection pump to determine the cam ring
rotation angle and the fuel injection pump speed. The
fuel temperature (FT) sensor is internal the PCU.
These values are used to compare the desired values
sent from the ECM then PCU determines the injection
timer piston position and fuel injection quantity, and
actuates timing control valve (TCV) & fuel injection
solenoid valve based on control maps in the PCU.
The fuel injection solenoid valve is installed to the fuel
injection pump rear side. The fuel injection event is
determined by this solenoid ON/OFF command. The
fuel injection solenoid valve cuts the fuel when the
engine shutoff (ESO) solenoid valve is commanded
shutoff from the PCU. (The fuel injection solenoid
valve and engine shutoff (ESO) solenoid valve is same
part. It calls ESO solenoid valve when fuel is shutoff.)
When the ignition switch is turned OFF or commanded
from fail-safe action, the ESO solenoid valve is
commanded shutoff to stop the engine running. If the
PCU detects that the fuel injection solenoid valve is
operated when the desired injection quantity from the
ECM is 0 mg/strk, this DTC will set.

Condition for Running the DTC

• The fuel injection pump CMP sensor signal is

generated.

• The CAN communication between the ECM and

PCU is normal.

Condition for Setting the DTC

• The PCU detects that the fuel injection solenoid

valve is operated when the desired fuel injection
quantity is commanded 0 mg/strk.

Action Taken When the DTC Sets

• The ECM illuminates the malfunction indicator

lamp (MIL) when the diagnostic runs and fails.

• The ECM cuts fuel injection.

Condition for Clearing the MIL/DTC

• The ECM turns OFF the MIL when the diagnostic

runs and does not fail.

• A history DTC clears after 40 consecutive driving

cycles without a fault. Or clear with the Tech 2.

Diagnostic Aids

• If an intermittent condition is suspected, refer to

Intermittent Conditions in this section.

Notice:

• Fuel injection solenoid valve is internal to the fuel

injection pump assembly.

• PCU is part of the fuel injection pump assembly.

DTC P0251 (Symptom Code 6) (Flash Code 53)

Step

Action

Value(s)

Yes

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic

System Check –

Engine Controls

Install the Tech 2.

Turn OFF the ignition for 30 seconds.

Start the engine and let idle for 30 seconds.

Accelerate the engine between idle and
W.O.T. (accelerator pedal full travel) many
times while observing the Diagnostic Trouble
Code (DTC) Information with the Tech 2.

Does the DTC fail this ignition?

—

Go to Step 3

Go to Step 4

Important:
The fuel injection pump must be timed to the
engine.

Replace the fuel injection pump. Refer to Fuel
Injection Pump Replacement in engine mechanical
section.

Did you complete the replacement?

—

Go to Step 4

—

Content .. 758 759 760 761 ..