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.
|
Preliminary
|
| • | Be sure driver understands transmission torque converter clutch
(TCC), and A/C compressor operation as explained in the owners manual. Inform
customer how TCC and the A/C clutch operates. |
|
Sensor/System
|
| • | 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 use of
improper RTV sealant. The sensors may have a white powdery
coating. Silicon contamination causes a high but false HO2S
signal voltage, rich exhaust indication. Refer to
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.
. The powertrain control module (PCM) will reduce the
amount of fuel delivered to the engine, causing a severe driveability
condition. |
| • | Inspect mass air flow (MAF) sensor and related wiring. |
| • | Inspect the air intake ducts for being collapsed, damaged areas,
looseness, improper installation, or leaking especially between the MAF
sensor and the throttle body. |
| • | Monitor the 24 X 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 24 X and CMP sensor circuits for intermittents.
Refer to
Testing for Intermittent Conditions and Poor Connections
in Wiring Systems. |
| • | Monitor the 3 X parameter on the scan tool. If the 3 X
is not responding, inspect the 7 X CKP sensor and circuits for intermittents.
Inspect the ignition control (IC) circuit, bypass circuit, 3 X reference
high circuit, and the 3 X reference low circuit for intermittents.
If these circuits become open or shorted, the conditions 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/cylinder. |
| • | Inspect any items which may cause an engine to run rich, long
term fuel trim is significantly in the negative range. Refer to
DTC P0172
Diagnostic Aids for DTC P0172. |
| • | Inspect any items that may cause an engine to run lean, long
term fuel trim is significantly in the positive range. Refer to
DTC P0171
Diagnostic Aids for DTC P0171. |
|
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
. Connect the other end
of the spark plug wire 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. |
| • | If spark is not present at the coils, inspect for the following
conditions: |
| - | Coils--Cracks, carbon tracking/arcing, or a resistance value
outside the specified range. |
Coil Resistance
5000-8000 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 foot (1 968 ohms per meter).
| | Important: : Spraying the secondary ignition wires with a light mist of water may
help locate an intermittent condition. Ignition voltage will arc to ground
when a secondary component is faulty.
|
| - | Defective ignition module. |
| - | Ignition system wiring--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 Inspection
. |
|
Additional
|
| • | Inspect the exhaust system for possible restriction: |
| - | Inspect exhaust system for damaged or collapsed pipes. |
| - | Inspect muffler for heat distress or possible internal failure. |
| - | Test for possible plugged catalytic converter by testing the
exhaust system back pressure. |
|
