Inspection/Test
| Action
|
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 position.
|
Preliminary
|
| • | Ensure the driver understands the transmission torque converter
clutch (TCC) and A/C compressor operation as explained in the owner's manual.
Inform the customer how the TCC and the A/C clutch operate. |
|
Sensor/System
|
Notice: Contamination of the oxygen sensor can result from the use of an inappropriate
RTV sealant (not oxygen sensor safe) or excessive engine coolant or oil consumption.
Remove the HO2S and visually inspect the portion of the sensor exposed to
the exhaust stream in order to check for contamination. If contaminated, the
portion of the sensor exposed to the exhaust stream will have a white powdery
coating. Silicon contamination causes a high but false HO2S signal voltage
(rich exhaust indication). The control module will then reduce the amount
of fuel delivered to the engine, causing a severe driveability problem. Eliminate
the source of contamination before replacing the oxygen sensor.
| • | Monitor the heated oxygen sensors (HO2S). The heated oxygen sensors
should respond quickly to different throttle positions. If not, inspect the
HO2S for silicon or other contaminants from fuel or from
the use of an improper RTV sealant. The sensors may have a
white powdery coating. Silicon contamination causes a high,
but false, HO2S signal voltage and a rich exhaust indication. The
powertrain control module (PCM) will reduce the amount of fuel
delivered to the engine, causing a severe driveability problem.
Refer to
Information Sensors/Switches Description
. |
| • | Inspect the MAF sensor and the related wiring. |
| • | Inspect the air intake ducts for collapsing, damaged areas, looseness,
improper installation, or leaking, especially between the MAF sensor and
the throttle body. |
| • | Monitor the 24X crankshaft position (CKP) sensor and the camshaft
position (CMP) sensor on scan tool. If neither sensor is responding, test
the sensor feed circuit. Both sensors use a separate feed circuit but are
internally connected to power. Test all of the 24X and the 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 the circuits for intermittents. Inspect the
ignition control (IC) circuit, the bypass circuit, the 3X reference high
circuit, and the 3X reference low circuit for intermittents. If these circuits
become open or shorted the circuits 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. |
|
Fuel System
|
| • | Ensure each injector harness is connected to the correct injector
and cylinder. |
| • | Inspect any items which may cause an engine to run rich. Refer
to the Diagnostic Aids for DTC P0172. |
| • | Inspect any items that may cause an engine to run lean. Refer
to the Diagnostic Aids for DTC P0171. |
|
Ignition System
|
| • | Inspect for the 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
spark tester. 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
spark tester. A crisp blue spark should be observed. |
| 5. | Repeat the above steps for each coil. |
| • | If spark is not present at the coils, inspect for the following
conditions: |
| - | Inspect the coils for cracks, carbon tracking or arcing, or a
resistance value outside the specified range. |
Coil Resistance
5000-8000 ohms | - | Inspect the spark plug wires for signs of arcing, cross firing,
cracks, carbon tracking, plug boot damage, pinching, improper routing, or
a resistance value outside the specified range. |
Spark Plug Wire Resistance
1 968 ohms per meter (600 ohms per foot).
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent problem. The ignition voltage will arc to ground
when a secondary component is faulty.
|
| - | Check for a faulty ignition module. |
| - | Check the ignition system wiring for a loose ignition module feed
or ground connection, or damaged system wiring. |
| • | Remove spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If the spark plugs are gas or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. Refer to
Spark Plug Visual Diagnosis
in Engine Electrical. |
|
Additional
|
| • | Inspect the exhaust system for restrictions: |
| - | Inspect the exhaust system for damaged or collapsed pipes. |
| - | Inspect the muffler for heat distress or internal failure. |
|
