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 the driver understands transmission torque converter
clutch (TCC), and A/C compressor operation as explained in the owners manual.
Inform the customer how the TCC and the A/C clutch operates. |
|
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 use of improper RTV sealant. The sensors
may have a white powdery coating. Silicon contamination causes
a high but false HO2S signal voltage, which is a rich exhaust
indication . The powertrain control module (PCM) will reduce
the amount of fuel delivered to the engine, causing a severe
driveability problem. |
| • | Inspect the mass air flow (MAF) sensor and related wiring. |
| • | Inspect the air intake ducts for the following conditions: |
| - | Leaking conditions especially between the MAF sensor and
the throttle body |
| • | 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. |
|
Fuel System
|
| • | Ensure each injector harness is connected to the correct injector
and/or cylinder. |
| • | Inspect any items which may cause an engine to run rich, and
the long-term fuel trim is significantly in the negative range. Refer to Diagnostic
Aids for
DTC P0172
. |
| • | Inspect any items that may cause an engine to run lean, and the
long-term fuel trim is significantly in the positive range. Refer to 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
. 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 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
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 spark plugs and inspect for the following conditions: |
| - | Burned or damaged electrodes |
| - | Improper heat range or reach |
| • | If spark plugs are fouled by gas or oil, the cause of the fouling
must be determined before replacing the spark plugs. Refer to
Spark Plug Inspection
. |
|
Additional
|
| • | Inspect the following components of the exhaust system for possible
restriction: |
| - | Inspect for damaged or collapsed pipes. |
| - | Inspect the muffler for heat distress or possible internal failure. |
| - | Test for possible plugged catalytic converter by testing the
exhaust system back pressure. |
|
