Inspection/Test
| Action
|
DEFINITION: Engine
runs unevenly at idle. If severe, the engine or vehicle may shake. Engine
idle speed may vary in RPM. Either condition may be severe
enough to stall the engine.
|
Preliminary
|
| • | Observe the owners driving habits. |
|
Fuel
System
|
| • | Test for faulty fuel injectors. Refer to the following test procedures: |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector
and/or cylinder. |
| • | Inspect for any items which may cause an engine to run rich,
long term fuel trim is significantly in the negative range. Refer to Diagnostic
Aids for
DTC P0172
. |
| • | Inspect for any items which may cause an engine to run lean,
long term fuel trim is significantly in the positive range. Refer to Diagnostic
Aids for
DTC P0171
. |
|
Sensor/System
|
| • | Test for conditions which cause an incorrect idle speed. |
| - | Restricted air intake system |
| • | Inspect the air intake ducts for the following conditions: |
| - | Leaking conditions especially between the mass air flow (MAF)
sensor and the throttle body |
| • | Inspect crankcase ventilation valve for proper operation. |
| • | Inspect the throttle position (TP) sensor and related wiring.
Refer to
DTC P0123
. |
| • | Monitor the 24X crankshaft position (CKP) and camshaft position
(CMP) sensors on scan tool. If both are not responding, test the sensor feed
circuit. Both sensors use a separate feed circuit but are internally
connected to power. Test all 24X and CMP sensor circuits for intermittents.
Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Monitor the 3X parameter on the scan tool. If the 3X is not responding,
inspect the 7X CKP sensor and circuits for intermittents. Inspect the ignition
control (IC) circuit, bypass circuit, 3X reference high circuit, and
the 3X reference low circuit for intermittents. If these circuits become
open, or shorted may not set a DTC immediately, but are capable of causing
driveability complaints. Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Inspect the transaxle range switch (TRS) input with the vehicle
in drive and the gear selector in drive or overdrive. |
|
Ignition
System
|
| • | Inspect for proper ignition voltage output using the following
steps: |
| 1. | Attach the J 26792
spark tester to engine ground. |
| 2. | Connect the spark plug end of the spark plug wire to the J 26792
. Leave the other end
of the spark plug wire connected to the coil being tested. |
| 3. | Connect the spark plug end of the companion spark plug wire to
ground. The companion spark plug wire is the wire attached to the corresponding
coil tower. |
| 4. | Crank the engine while observing the J 26792
. A spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition voltage will arc to ground when
a secondary component is faulty.
|
| • | If spark is not present at the coils, inspect the following components
for the specified conditions: |
| - | Coils--Cracks, carbon tracking and/or arcing, or a resistance
value outside the specified range |
Coil Resistance
5000-8000 ohms (5K-8K ohms)
Spark Plug Wire Resistance
9868 ohms per meter (3000 ohms per foot)
| • | A resistance value outside the specified range |
| - | Defective ignition module. |
| - | Ignition system wiring--Loose ignition module feed or ground
connection, or damaged system wiring |
| • | Remove the spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. Refer to
Spark Plug Inspection
. |
|
Engine
Mechanical
|
| • | Inspect engine mechanical for the following conditions: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber due to leaking valve seals |
| • | Inspect the following components for incorrect basic engine parts: |
|
Additional
| Inspect the
following components of the exhaust system for possible restrictions:
| • | Inspect for damaged or collapsed pipes. |
| • | Inspect the mufflers for heat distress or possible internal failure. |
| • | Test for possible plugged catalytic converter by testing the
exhaust system back pressure. |
| • | An engine miss condition can be caused by electromagnetic interference
(EMI) on the reference circuit. EMI can usually be detected by monitoring
engine RPM with a scan tool. A sudden increase in RPM
with little change in actual engine RPM change, indicates
EMI is present. If a problem exists, inspect the routing of
secondary ignition wires, high voltage components, e.g. near
ignition control circuits. |
| • | Inspect for intake and exhaust manifold passages for casting
flash. |
|
