Checks
| Action
|
DEFINITION: Engine
power variation under steady throttle or cruise. Feels like the vehicle speeds
up and slows down without a change in the accelerator pedal
position.
|
Preliminary
|
| • | Be sure the driver understands the operation of 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 operates. |
|
Sensor/System
|
| • | Test the heated oxygen sensors (HO2S). The HO2S should respond
quickly to the different throttle positions. If they do not, inspect
the HO2S for silicon or other contaminates from fuel or the
use of improper RTV sealant. The sensors may have a white powdery coating.
This type of contamination may result in a rich exhaust indication. The
engine control module (ECM) will then reduce the amount of fuel delivered
to the engine, causing a severe driveability condition. |
| • | Inspect the intake air ducts for proper installation and for leaks. |
| • | Inspect the mass air flow (MAF) sensor connections. Repair or
replace the terminals. Refer to
Connector Repairs
in Wiring Systems. |
|
Fuel System
|
| • | Test for incorrect fuel pressure. |
| • | Test for a restricted fuel filter. |
| • | Verify that each injector harness is connected to the correct
injector/cylinder. Relocate injector harnesses as necessary. |
| • | Test the items which can cause an engine to run rich (long term
fuel trim near -13 percent). For a rich condition, refer to
DTC P0172 or P0175
. |
| • | Test the items that can cause an engine to run lean (long term
fuel trim near 23 percent). For a lean condition, refer to
DTC P0171 or P0174
. |
|
Ignition System
|
| • | Inspect for proper installation of the ignition coil seal. Improper
installation may allow water to enter spark plug area. Inspect for evidence
of water that may have evaporated. |
| • | Test for proper ignition voltage output with a J 26792
Spark Tester. Refer to
Electronic Ignition (EI) System Diagnosis
. If you suspect secondary
ignition system leakage, perform the procedure in the Diagnostic Aids portion
of the Ignition System Check. |
| • | Remove the spark plugs and inspect for the following conditions: |
| • | An improper spark plug gap may cause a driveability condition.
Gap the spark plugs using a wire gauge 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
Spark Plug Inspection
. Once you determine the
cause of the fouling, refer to one of the following procedures: |
| - | For diagnosis of coolant contaminated spark plugs, refer to
Loss of Coolant
in Engine Cooling. |
|
Additional Checks
|
| • | Visually/physically inspect vacuum hoses for splits, kinks, and
proper connections and routing as shown on the vehicle emission control information
label. Refer to
Emission Hose Routing Diagram
. |
| • | Inspect the exhaust system for the following conditions: |
| - | Damaged or collapsed pipes |
| - | Heat distress or for an internal failure of the muffler |
| • | Test the transmission torque converter clutch (TCC) operation.
A TCC applying too soon can cause the engine to spark knock. Refer to
Torque Converter Diagnosis
in Automatic
Transmission-4L30-E. |
|
