Checks
| 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 Checks
|
| • | Refer to Important Preliminary Checks in
Symptoms
. |
| • | Refer to Visual/Physical Checks in
Symptoms
. |
|
Fuel System
|
| • | Test the fuel injectors using the following tests: |
| • | Inspect for fuel in the pressure regulator vacuum hose. |
| • | Ensure each injector harness is connected to the correct injector/cylinder. |
| • | Test items which can cause an engine to run rich. Long Term Fuel
Trim is significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172 Fuel Trim System Rich
. |
| • | Inspect items that can cause an engine to run lean. Long Term
Fuel Trim is significantly in the positive range. Refer to Diagnostic Aids
for
DTC P0171 Fuel Trim System Lean
. |
|
Sensor/System
|
| • | Inspect for conditions which cause an incorrect idle speed. |
| • | Test the transaxle range switch input with the vehicle in drive
and the gear selector in drive or overdrive. |
|
Ignition System
|
| • | Test for proper ignition voltage output using the following steps: |
| - | Clip the J 26792
spark tester to engine ground. |
| - | Connect one end of a spark plug wire to the spark tester. Leave
the other end of the spark plug wire to the coil being tested. |
| - | Connect one end of another spark plug wire to the other coil tower.
Connect the other end of the spark plug wire to ground. |
| - | Crank the engine while observing the spark tester. A crisp blue
spark should be observed. |
| - | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, check for the following
conditions: |
| - | Coils -- Cracks, carbon tracking/arcing, or a secondary resistance
value outside the specified range. |
Coil Resistance
5,000-8,000 ohms (5K-8K ohms) | - | Spark plug wires -- Signs of arcing/cross firing, cracks,
carbon tracking, plug boot damage, pinched, improper routing, or a resistance
value outside the specified range. |
Spark Plug Wire Resistance
600 ohms per ft
| | Important: Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. Ignition components will arc to ground
when a secondary component is faulty.
|
| - | Ignition system wiring -- Loose ignition module feed or ground
connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following: |
| - | 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. |
|
Engine Mechanical
|
| • | Test and inspect engine mechanical for the following: |
| - | Sticking or leaking valves |
| - | Excessive oil in combustion chamber -- Leaking valve seals. |
| • | For incorrect basic engine parts -- Inspect the following: |
|
Additional Checks
|
| • | Test exhaust system for possible restrictions. Inspect for the
following: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect mufflers for heat distress or possible internal failure. |
| • | Inspect for faulty motor mounts. |
| • | 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,
near the ignition control circuits. |
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