Isuzu N-Series. Manual - part 722

6E-310    Engine Control System (4HK1) 

Symptoms – Engine Controls

Symptoms – Engine Controls

Important Preliminary Inspections Before Starting
Perform Diagnostic System Check – Engine Controls
before using the symptom tables, and verify that all of
the following are true:

• The engine control module (ECM) and malfunction

indicator lamp (MIL) are operating correctly.

• There are no diagnostic trouble codes (DTCs)

stored, or a DTC exists but without the MIL.

• The Tech 2 data is within the normal operating

range. Refer to Tech 2 Data List in this section.

• Verify the customer concern and locate the correct

symptom in the table of contents. Inspect the items
indicated under that symptom.

Visual and Physical Inspection
Several of the symptom procedures ask for careful
visual and physical inspection. This step is extremely
important. The visual and physical inspection can lead
to correcting a problem without further inspections, and
can save valuable time. Ensure that:

• The ECM grounds are clean, tight, and in their

proper location.

• The vacuum hoses are not split or kinked, and

properly connected. Inspect throughly for any type
of leak or restriction.

• The air intake ducts are not collapsed or damaged.
• The engine harness wiring and terminals are

properly connected and are not pinched or cut.

Intermittent
Important:
Inspect for improper installation of electrical
components if an intermittent condition exists. Inspect
for aftermarket add-on electrical equipment devices,
lights, and cellular phones. Verify that no aftermarket
equipment is connected to the keyword 2000 serial
data circuit. If you cannot locate an intermittent
condition, a cellular phone communication signal may
cause the condition.

Important:
The problem may or may not turn ON the MIL or store a
DTC.

Faulty electrical connections or wiring cause most
intermittent problems. Perform a careful visual and
physical inspection of the suspect connectors for the
following conditions:

• Improperly mated connector halves
• Terminals that are not seated
• Terminals that are damaged or improperly formed

Reform or replace connector terminals in the problem
circuit in order to ensure proper contact tension.
Remove the terminal from the connector body in order
to inspect for poor terminal wire connection.
Road test the vehicle with the DMM connected to the
suspected circuit. An abnormal reading that occurs
when the malfunction occurs is a good indication that
there is a malfunction in the circuit being monitored.
Use the Tech 2 in order to help detect intermittent
conditions. Useful features of the Tech 2 include the
following:

• Trigger the Snapshot feature in order to capture

and store engine parameters when the malfunction
occurs. Review this stored information in order to
see the specific running conditions that caused the
malfunction.

• Use the Plot Function on the Tech 2 in order to plot

selected data parameters. Review this stored
information to aid in locating an intermittent
problem. Refer to the Tech 2 Users Guide for more
information.

Important:
If the intermittent condition exists as a start and then
stall, test for DTCs relating to the vehicle theft deterrent
system. Test for improper installation of electrical
options such as lights, cellular phones, etc.

Any of the following may cause an intermittent MIL with
no stored DTC:

• The ECM grounds are loose or dirty. Refer to

Engine Controls Schematics.

• The MIL circuit intermittently shorted to ground.
• Electrical system interference caused by a

malfunctioning relay, ECM driven solenoid, or
switch. The electrical component can cause a
sharp electrical surge. Normally, the problem will
occur when the malfunctioning component is
operating.

• There are any open diodes.

Important:
The following symptom tables contain groups of
possible causes for each symptom. The order of these
procedures is not important. If the Tech 2 readings do
not indicate the problems, then proceed in a logical
order, easiest to check or most likely to cause first. In
order to determine if a specific vehicle is using a
particular system or component, refer to Engine
Controls Schematics for an application.

Use the following tables when diagnosing a symptom
complaint:

• Intermittent Conditions
• Hard Start
• Rough, Unstable, or Incorrect Idle and Stalling

 Engine Control System (4HK1)    6E-311

• High Idle
• Cuts Out, Misses
• Surge / Chuggles
• Lack of Power, Sluggishness, or Sponginess
• Hesitation, Sag, Stumble

• Fuel Knock / Combustion Noise
• Poor Fuel Economy
• Excessive Smoke (Black Smoke)
• Excessive Smoke (White Smoke)

Intermittent Conditions

Checks

Action

DEFINITION: The problem is not currently present but is indicated in DTC History.
OR
There is a customer complaint, but the symptom cannot currently be duplicated, if the problem is not DTC related.

Preliminary Checks

• Refer to Symptoms – Engine Controls before starting.

Harness / Connector

Many intermittent open or shorted circuits are affected by harness / connector
movement that is caused by vibration, engine torque, bumps / rough pavement, etc.
Test for this type of condition by performing the applicable procedure from the following
list:

• Move related connectors and wiring while monitoring the appropriate Tech 2 data.
• Move related connectors and wiring with the component commanded ON, and

OFF, with the Tech 2. Observe the component operation.

• With the engine running, move related connectors and wiring while monitoring

engine operation.

If harness or connector movement affects the data displayed, component / system
operation, or engine operation, inspect and repair the harness / connections as
necessary.
Refer to Electrical Connections or Wiring.

Electrical Connections or Wiring

Poor electrical connections, terminal tension or wiring problems cause most
intermittent. To perform the following inspections:

• Inspect for poor mating of the connector halves, or terminals improperly seated in

the connector body.

• Inspect for improperly formed or damaged terminals. Test for poor terminal tension.
• Inspect for poor terminal to wire connections including terminals crimped over

insulation. This requires removing the terminal from the connector body.

• Inspect for corrosion / water intrusion. Pierced or damaged insulation can allow

moisture to enter the wiring. The conductor can corrode inside the insulation, with
little visible evidence. Look for swollen and stiff sections of wire in the suspect
circuits.

• Inspect for wires that are broken inside the insulation.
• Inspect the harness for pinched, cut or rubbed through wiring.
• Ensure that the wiring does not come in contact with hot exhaust components.

Control Module Power and Grounds
Component Power and Grounds

Poor power or ground connections can cause widely varying symptoms.

• Test all control module power supply circuits. Many vehicles have multiple circuits

supplying power to the control module. Other components in the system may have
separate power supply circuits that may also need to be tested. Inspect
connections at the module / component connectors, fuses, and any intermediate
connections between the power source and the module / component. A test lamp
or a DMM may indicate that voltage is present, but neither tests the ability of the
circuit to carry sufficient current. Ensure that the circuit can carry the current
necessary to operate the component.

• Test all control module ground and system ground circuits. The control module may

have multiple ground circuits. Other components in the system may have separate
grounds that may also need to be tested. Inspect grounds for clean and tight
connections at the grounding point. Inspect the connections at the component and
in splice packs, where applicable. Ensure that the circuit can carry the current
necessary to operate the component.

6E-312    Engine Control System (4HK1) 

Hard Start

Temperature Sensitivity

• An intermittent condition may occur when a component / connection reaches

normal operating temperature. The condition may occur only when the component /
connection is cold, or only when the component / connection is hot.

• If the intermittent is related to heat, review the data for a relationship with the

following:

- High ambient temperatures
- Underhood / engine generated heat
- Circuit generated heat due to a poor connection, or high electrical load
- Higher than normal load conditions, towing, etc.

• If the intermittent is related to cold, review the data for the following:

- Low ambient temperatures-In extremely low temperatures, ice may form in a

connection or component. Test for water intrusion.

- The condition only occurs on a cold start.
- The condition goes away when the vehicle warms up.

• Information from the customer may help to determine if the trouble follows a pattern

that is temperature related.

Electromagnetic Interference (EMI)
and Electrical Noise

Some electrical components / circuits are sensitive to EMI or other types of electrical
noise. Inspect for the following conditions:

• A misrouted harness that is too close to high voltage / high current devices such as

injection components, motors, generator etc. These components may induce
electrical noise on a circuit that could interfere with normal circuit operation.

• Electrical system interference caused by a malfunctioning relay, or the engine

control module (ECM) driven solenoid or switch. These conditions can cause a
sharp electrical surge. Normally, the problem will occur when the malfunctioning
component is operating.

• Improper installation of non-factory or aftermarket add on accessories such as

lights, 2-way radios, amplifiers, electric motors, remote starters, alarm systems, cell
phones, etc. These accessories may lead to an emission related failure while in
use, but do not fail when the accessories are not in use.

• Test for any open diodes. Some relays may contain a clamping diode.
• Test the generator for a bad rectifier bridge that may be allowing AC noise into the

electrical system.

Duplicating Failure Conditions

• If none of the previous tests are successful, attempt to duplicate and/or capture the

failure conditions.

• An alternate method is to drive the vehicle with the DMM connected to a suspected

circuit. An abnormal reading on the DMM when the problem occurs, may help you
locate the problem.

Tech 2 Snapshot

The Tech 2 can be set up to take a Snapshot of the parameters available via serial
data. The Snapshot function records live data over a period of time. The recorded data
can be played back and analyzed. The Tech 2 can also graph parameters singly or in
combinations of parameters for comparison. The Snapshot can be triggered manually
at the time the symptom is noticed, or set up in advance to trigger when a DTC sets.
An abnormal value captured in the recorded data may point to a system or component
that needs to be investigated further.
Refer to the Tech 2 user instructions for more information on the Snapshot function.

Checks

Action

DEFINITION: The engine cranks OK, but does not start for a long time. The engine does eventually run, or may start but
immediately dies.

Checks

Action

 Engine Control System (4HK1)    6E-313

Preliminary Checks

• Diagnostic System Check – Engine Controls.
• Ensure the driver is using the correct starting procedure.
• Inspect the engine control module (ECM) grounds for being clean, tight, and in their

proper locations.

• Inspect that the harness connectors are correctly connected.
• Inspect the fuel type and quality.
• Inspect the programmed fuel injector ID code for each cylinder.
• Inspect the Tech 2 Data List in this section.

Sensor Checks

Inspect the engine control sensors for the following conditions. Refer to the Tech 2
Data List in this section.

• Use the Tech 2 to compare the Coolant Temperature with the Intake Air

Temperature (IAT) and Fuel Temperature (FT) on a cold engine condition. If the
difference among temperature reading is more than 5

°C (9°F) on a cold engine,

check for high resistance on the low reference circuit and signal circuit or for a
skewed sensor.

• Use the Tech 2 to observe the Fuel Rail Pressure (FRP) Sensor parameter with the

engine OFF. The FRP Sensor on the Tech 2 should read 0.9 – 1.0 volt with the key
ON and engine OFF after the engine has stopped running for a minimum of 2
minutes. If not, check for high resistance in the 5 volts reference circuit, low
reference circuit, signal circuits or for a skewed sensor.

• Inspect the crankshaft position (CKP) sensor is tight and the flywheel teeth are not

damaged.

• Inspect the camshaft position (CMP) sensor is tight and the camshaft gear flange

surface is not damaged.

Fuel System Checks

Inspect the fuel system for the following conditions. Refer to Fuel System Check Chart
and appropriate procedure in the Fuel System section.

• Inspect for air in the fuel system.
• Inspect for water contamination in the fuel.
• Inspect for external fuel leaks or high engine oil level.
• Measure the fuel return rate from the fuel injectors.
• Inspect the fuel lines between the fuel tank and fuel supply pump for being crushed

or kinked.

• Inspect for a plugged fuel tank vent hose.
• Inspect inside the fuel tank for any foreign material that may be getting drawn into

the fuel line pickup causing a blocked condition.

• Inspect the fuel lines between the fuel tank and fuel supply pump for tightness and

all fuel hoses for cuts, cracks and for the use of proper clamps.

• Inspect the fuel supply pump operation.

Notice:
The fuel supply pump must be timed to the engine and adjustment value must be
learned to the ECM.

• Perform the Injector Balancing test with the Tech 2. Repair the wire or replace the

appropriate fuel injector that does not change engine speed when commanded
OFF.

• Perform the Injector Forced Drive test with the Tech 2. Repair the wire or replace

the appropriate fuel injector that does not create a clicking noise (solenoid
operating noise), contents an interrupted noise or has abnormal nose when
commanded ON.

• Inspect the fuel rail pressure (FRP) regulator feedback current on the Tech 2.

Air Intake System Checks

Inspect the air intake system for the following conditions.

• Inspect the air cleaner and air intake ducts for a restriction, holes, or leaks.
• Inspect for a restriction in the turbocharger inlet duct.
• Inspect the intake throttle valve for a stuck closed position.
• Inspect for a restriction or leak in the intake manifold.

Checks

Action