Isuzu engine C22NE / 22LE / 20LE. Manual — part 63
DRIVEABILITY AND EMISSIONS 6E1-81
SYMPTOM DIAGNOSIS
PRELIMINARY CHECKS
Before using this section, perform the "On-Board
Diagnostic (OBD) System Check" and verify all of the
following items:
• The engine control module (ECM) and malfunction
indicator lamp (MIL) (Check Engine lamp) are
operating correctly.
• There are no Diagnostic Trouble Code(s) stored.
• Scan Tool data is within normal operating range.
Refer to Typical Scan Data Values.
• Verify the customer complaint and locate the
correct symptom in the table of contents. Perform
the procedure included in the symptom chart.
VISUAL/PHYSICAL CHECK
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time. This check should include the following items:
• ECM grounds for cleanliness, tightness and proper
location.
• Vacuum hoses for splits, kinks, and proper
connections, shown on the " Emission Control
System Schematics". Check thoroughly for any type
of leak or restriction.
• Air intake ducts for collapsed or damaged areas.
• Air leaks at throttle body mounting area, manifold
absolute pressure (MAP) sensor and intake
manifold sealing surfaces.
• Ignition wires for cracking, hardness, and carbon
tracking.
• Wiring for proper connections, pinches and cuts.
INTERMITTENT
Important: An intermittent problem may or may not
turn on the malfunction indicator lamp (MIL) or store a
Diagnostic Trouble Code. DO NOT use the Diagnostic
Trouble Code (Diagnostic Trouble Code) charts for
intermittent problems. The fault must be present to
locate the problem.
Most intermittent problems are caused by faulty
electrical connections or wiring. Perform a careful
visual/physical check for the following conditions.
• Poor mating of the connector halves or a terminal
not fully seated in the connector (backed out).
• Improperly formed or damaged terminal.
• All connector terminals in the problem circuit should
be carefully checked for proper contact tension.
• Poor terminal-to-wire connection. This requires
removing the terminal from the connector body to
check.
• Ignition coil shorted to ground and arcing at ignition
wires or plugs.
• MIL (Check Engine lamp) wire to ECM shorted to
ground.
• Poor ECM grounds. Refer to the ECM wiring
diagrams.
Road test the vehicle with a 5-8840-2392-0 Digital
Multimeter connected to a suspected circuit. An
abnormal voltage when the malfunction occurs is a
good indication that there is a fault in the circuit being
monitored.
Use a Scan Tool to help detect intermittent conditions.
The Scan Tools have several features that can be
used to locate an intermittent condition. Use the
following features to find intermittent faults:
To check for loss of diagnostic code memory,
disconnect the MAP sensor and idle the engine until
the MIL (Check Engine lamp) comes on. Diagnostic
Trouble Code 34 should be stored and kept in memory
when the ignition is turned "OFF." If not, the ECM is
faulty. When this test is completed, make sure that
you clear the Diagnostic Trouble Code 34 from
memory.
Check for improper installation of electrical options
such as lights, cellular phones, etc. Check all wires
from the ECM to the ignition control module for poor
connections.
Check for an open diode across the A/C compressor
clutch and check for other open diodes (refer to wiring
diagrams in Electrical Diagnosis).
If problem has not been found, refer to ECM
Connector Symptom tables.
6E1-82 DRIVEABILITY AND EMISSIONS
Hard Start Symptom
Step
Action
Value(s)
Yes
No
DEFINITION: Engine cranks, but does not start for a long time. Does eventually run, or may start but immediately
stalls.
1
Was the On-Board Diagnostic (OBD) System Check
performed?
-
Go to Step 2
Go to OBD
System
Check
2
1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found,
correct the condition as instructed in the bulletin.
Was a bulletin found that addresses the symptom?
-
Verify Repair
Go to Step 3
3
Was a visual/physical check performed?
-
Go to Step 4
Go to
Visual/Physic
al Check
4
Check engine coolant temperature (ECT) sensor for shift
in value.
1. After 8 hours with the hood up and the engine not
running, connect the Scan Tool.
2. Ignition ON, engine not running.
3. Using the Scan Tool, compare Engine Coolant
Temperature to Intake Air Temperature.
Are ECT and IAT within the specified value of each other?
±5°C
(
±9°F)
Go to Step 8
Go to Step 5
5
1. Using a Scan Tool, display the engine coolant
temperature and note the value.
2. Check the resistance of the engine coolant
temperature sensor.
3. Refer to Temperature vs. Resistance chart in
Diagnostic Trouble Code 14 for resistance
specifications.
Is the actual resistance near the resistance value in the
chart for the temperature that was noted?
-
Go to Step 7
Go to Step 6
6
Replace the ECT sensor.
Is the action complete?
-
Verify repair
-
7
Located and repair high resistance or connection in the
ECT signal circuit or the ECT signal circuit or the ECM
sensor ground.
-
Verify repair
-
8
Check for a faulty, plugged, or incorrectly installed PCV
hoses.
Was a problem found?
-
Verify repair
Go to Step 9
9
Visually/Physically inspect the secondary ignition wires.
Check for the following conditions:
• Verify that all ignition wire resistance are less than the
specified value.
• Verify that ignition wires are correctly routed to eliminate
cross-firing.
• Verify that ignition wires are not arcing to ground.
Spraying the secondary ignition wires with a light mist of
water may help locate an intermittent problem.
Was a problem found?
#1 cyl. 4.7k
Ω
#2 cyl. 3.9k
Ω
#3 cyl. 3.4k
Ω
#4 cyl. 3.1k
Ω
Verify repair
Go to Step 10
DRIVEABILITY AND EMISSIONS 6E1-83
Hard Start Symptom (Cont'd)
Step
Action
Value(s)
Yes
No
10
Check for proper ignition voltage output with a spark tester
(Use commercially available tool).
Was a problem found?
-
Verify repair
Go to Step 11
11
1. Remove the spark plugs and check for gas or oil
fouling cracks, wear, improper gap, burned electrodes,
heavy deposits, or improper heat range.
If spark plugs are fouled, the cause of fouling must be
determined before replacing the spark plugs.
Was a problem found?
-
Verify repair
Go to Step 12
12
Check for a loose ignition control module ground.
Was a problem found?
-
Verify repair
Go to Step 13
13
1. Check the ignition coil secondary resistance.
2. Replace the coil if it is greater than the specified
resistance.
Did the coil require replacement?
2.5 k
Ω
Verify repair
Go to Step 14
14
Check IAC operation. Perform the procedure in the
diagnostic chart Diagnostic Trouble Code 35, Step 6.
Was a problem found?
-
Verify repair
Go to Step 15
15
Check for water or alcohol contaminated fuel.
Was a problem found?
-
Verify repair
Go to Step 16
16
Perform the procedure in Fuel System Pressure Test to
determine if there is a problem with fuel delivery.
Was a problem found?
-
Verify repair
Go to Step 17
17
Check for the following engine mechanical problems (refer
to Engine Mechanical):
• Low compression
• Leaking cylinder head gaskets
• Worn camshaft
• Camshaft drive belt slipped or stripped
Was a problem found?
-
Verify repair
Go to Step 18
18
1. Review all diagnostic procedures within this table.
2. If all procedures have been completed and no
malfunctions have been found, review/inspect the
following:
• Visual/physical inspection
• Scan Tool data
• All electrical connections within a suspected circuit
and/or system
Was a problem found?
-
Verify repair
Contact
Technical
Assistance
6E1-84 DRIVEABILITY AND EMISSIONS
Surges and/or Chuggles Symptom
Step
Action
Value(s)
Yes
No
DEFINITION: Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows
down with no change in the accelerator pedal.
1
Was the On-Board Diagnostic (OBD) System Check
performed?
-
Go to Step 2
Go to OBD
System
Check
2
1. Perform a bulletin search.
2. If a bulletin that addresses the symptom is found,
correct the condition as instructed in the bulletin.
Was a bulletin found that addresses the symptom?
-
Verify Repair
Go to Step 3
3
Was a visual/physical check performed?
-
Go to Step 4
Go to Visual/
Physical
Check
4
Be sure that the driver understands A/C compressor
operation as explained in the owner's manual.
Inform the customer how the A/C clutch operate.
Is the customer experiencing a normal condition?
-
System OK
Go to Step 5
5
Check the fuel control Heated Oxygen Sensor (HO2S) (If
applicable). When monitored on the Scan Tool, the HO2S
should respond quickly to different throttle positions. If it
doesn't check for silicon or other contaminants from fuel or
use of improper RTV sealant. The sensors may have a
white powdery coating. Silicon contamination sends a rich
exhaust signal which causes the ECM to command an
excessively lean air/fuel mixture.
Was a problem found?
-
Verify repair
Go to Step 6
6
Check the fuel pressure. Refer to Fuel System Pressure
Test.
Was a problem found?
-
Verify repair
Go to Step 7
7
Monitor "02 Status" on the Scan Tool (If applicable).
Is "02 Status" in the (rich condition)?
-
Go to Step 8
Go to Step 9
8
Check items that can cause the engine to run rich.
Refer to Diagnostic Aids in Diagnostic Trouble Code 45 (If
applicable).
Was a problem found?
-
Verify repair
Go to Step 10
9
Check items that can cause the engine to run lean.
Refer to Diagnostic Aids in Diagnostic Trouble Code 44 (If
applicable).
Was a problem found?
-
Verify repair
Go to Step 10
10
Check for proper ignition voltage output with the spark
tester (Use commercially available tool).
Was a problem found?
-
Verify repair
Go to Step 11
11
Check for a loose ignition control module ground.
Was a problem found?
-
Verify repair
Go to Step 12
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