Isuzu N-Series. Manual - part 747

 Engine Control System (4JH1)    6E-39

15

Replace the ECM main relay.

Did you complete the replacement?

—

Go to Step 17

—

16

Important:
Replacement ECM must be programmed.

Replace the ECM.  Refer to Engine Control Module
(ECM) Replacement in this section.

Did you complete the replacement?

—

Go to Step 17

—

17

1.

Turn OFF the ignition.

2.

Reconnect all disconnected connectors.

3.

Turn ON the ignition, with the engine OFF.

4.

Attempt to establish Tech 2 communications
with the ECM.

Does the Tech 2 communicate with the ECM?

—

System OK

Go to Step 3

Step

Action

Value(s)

Yes

No

6E-40    Engine Control System (4JH1) 

Engine Cranks but Does Not Run

Description
The Engine Cranks but Does Not Run diagnostic table
is an organized approach to identifying a condition that
causes an engine to not start.  The diagnostic table
directs the service technician to the appropriate system
diagnosis.  The diagnostic table assumes the following
conditions are met:

• The battery is completely charged and terminals

are cleaned and tight.

• The engine cranking speed is normal.

• There is adequate fuel in the fuel tank.
• There is no fuel leak in the fuel line.
• There is no air in the fuel line.
• Filters (Air, Fuel) are clean.
• Fuse and slow blow fuse are normal.

Diagnostic Aids
If an intermittent condition is suspected, refer to
Intermittent Conditions in this section.

Engine Cranks but Does Not Run

Step

Action

Value(s)

Yes

No

1

Did you perform the Diagnostic System Check –
Engine Controls?

—

Go to Step 2

Go to Diagnostic 

System Check – 

Engine Controls

2

1.

Install the Tech 2.

2.

Turn OFF the ignition for 30 seconds.

3.

Crank the engine for specified amount of time.

4.

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

Does the Tech 2 display any DTCs that failed this
ignition?

15 seconds

Go to Diagnostic 

Trouble Code (DTC) 

List

Go to Step 3

3

1.

Check for normal readings at key up for the
following inputs and output: Refer to the Tech
2 Data List or a known good vehicle to
determine normal values.

• System  Voltage
• Engine Coolant Temperature (ECT)
• Intake Air Temperature (IAT)
• Mass Air Flow (MAF) Sensor
• Barometric Pressure 

2.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 4

 Engine Control System (4JH1)    6E-41

4

1.

Inspect the high pressure side between the
fuel injection pump and the fuel injection
nozzles for fuel leakage.  The following
components may contain an external leak.

• Fuel injection pump
• Fuel injection pump control unit (PCU)
• Fuel injection solenoid valve
• Timing control valve (TCV)
• Constant pressure valve (CPV)
• Fuel pipe between the fuel injection

pump and fuel injection nozzles

• Each fuel pipe sleeve nuts
• Each fuel pipe connectors
• Each gaskets

Notice:
Fuel may leak into the engine from the fuel injection
pump.  In such case, the engine oil level will rise.
Inspect for fuel leakage into the engine oil.

2.

Repair any fuel system leaks as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 5

5

1.

Turn OFF the ignition.

2.

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.

3.

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.

4.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 6

6

1.

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

2.

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

3.

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.

4.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 7

Step

Action

Value(s)

Yes

No

6E-42    Engine Control System (4JH1) 

7

1.

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.  

2.

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.

3.

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.

4.

Repair any fuel system leaks and restrictions
as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 8

8

1.

Other possible causes for the no-start
condition:

• Fuel injection pump mechanical timing

incorrect

• Flywheel installed incorrectly causing the

crankshaft position (CKP) sensor to be
incorrectly timed to the engine.
Disconnect sensor and attempt to start
engine to verify.

• Heavily restricted intake, exhaust or

catalytic converter plugged solid

• Poor engine compression
• Water or gasoline contamination in fuel

2.

Repair or replace as necessary.

Did you find and correct the condition?

—

Go to Step 10

Go to Step 9

9

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 10

—

10

1.

Reconnect all previously disconnected
harness connector(s).

2.

Turn OFF the ignition for 30 seconds.

3.

Attempt to start the engine.

Does the engine start and continue to run?

—

Go to Step 11

Go to Step 2

11

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

No