Checks
| 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 (APP)
|
Preliminary
|
| • | Inspect the powertrain control module (PCM) grounds for being
clean, tight, and in the proper locations. Refer to
Engine Controls Schematics
. |
| • | Be sure the driver understands the operation of the transmission
torque converter clutch (TCC) and A/C compressor operation. Inform the customer
how the TCC and the A/C clutch operates. |
|
Sensor/System
|
| • | Inspect the heated oxygen sensors (HO2S). The HO2S should respond
quickly to different throttle positions (TP). If you do not, check the HO2S
for silicon or other contaminates from fuel or the use of improper RTV sealant.
The sensors may have a white, powdery coating and result in a high but false
signal voltage rich exhaust indication. The powertrain control module (PCM)
will then reduce the amount of fuel delivered to the engine causing a severe
driveability problem. For more information, refer to
Oil Consumption Diagnosis
in Engine Mechanical 8.1L. |
| • | Inspect the mass airflow (MAF) sensor connections. Repair or
replace terminals. Refer to
Connector Repairs
in Wiring Systems. |
|
Fuel
System
|
| • | Inspect that each injector harness is connected to the correct
injector or cylinder according to the firing order firing order: 1-8-7-2-6-5-4-3.
Relocate injector harnesses as necessary. |
| • | Inspect the items that cause an engine to run rich long term
fuel trim near -13 percent. For a rich condition, refer to
DTC P0172 or P0175
. |
| • | Inspect the items that can cause an engine to run lean long term
fuel trim near 24 percent. For a lean condition, refer to
DTC P0171 or P0174
. |
|
Ignition
System
|
| • | Wet down the secondary ignition system with water from a spray
bottle. Wetting down the secondary ignition system may help locate damaged
or deteriorated components. Look and listen for arcing or misfiring as
you apply the water. |
| • | Remove the spark plugs and check for the following: |
| • | An improper spark plug gap will cause a driveability problem.
Gap the spark plugs using a wire gage gap tool. Refer to
Spark Plug Replacement
. |
| • | Determine the cause of the fouling before replacing the spark
plugs if the spark plugs are gas, coolant, or oil fouled. Refer to one of
the following procedures: |
| • | Monitor the Misfire Current Counters while driving the vehicle
in the conditions that the misfire occurred. If a cylinder can be located
with a misfire, use the DTC P0300 table for diagnosis. |
|
Engine
Mechanical
| Ensure that the engine coolant temperature (ECT) is not above 130°C (266°F).
This condition causes the PCM to operate in Engine Coolant Over Temperature-Fuel
Disabled Mode. While in Engine Coolant Over Temperature-Fuel Disabled
Mode, the PCM turns fuel OFF to four cylinders at a time to keep engine
temperatures from reaching damaging levels. The system perceives Engine
Coolant Over Temperature-Fuel Disabled Mode as a lack of power, miss,
or rough idle. If the vehicle operates in Engine Coolant Over Temperature-Fuel
Disabled Mode, refer to
Engine Overheating
in
Engine Cooling for diagnosis.
|
Additional Checks
|
| • | Visually/physically inspect the vacuum hoses for splits, kinks,
and proper connections and routing as shown on Vehicle Emission Control Information
label. |
|
