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.
|
Preliminary
|
| • | Search for service bulletins. |
| • | Be sure the driver understands the transmission torque converter
clutch (TCC), and the A/C compressor operation as explained in the owners
manual. Inform the customer how the TCC and the A/C clutch operates. |
| • | Inspect the powertrain control module (PCM) grounds for being
clean, tight, and in their proper location. |
|
Sensor/System
|
| • | Inspect the oxygen sensor (O2S 1) and the heated oxygen
sensor (HO2S 2). The O2S 1 and HO2S 2 should respond
quickly to different throttle positions. If not, check the O2S 1
and the HO2S 2 for silicon or other contaminants from fuel or
the use of improper RTV sealant. The sensors may have a white powdery
coating. Silicon contamination causes a high but false O2S 1 and
HO2S 2 signal voltage, rich exhaust indication. The PCM will
reduce the amount of fuel delivered to the engine, causing a severe
driveability problem. |
| • | Inspect crankshaft position (CKP) sensor active counter for steady
count. |
| • | Inspect for proper operation of the manifold absolute pressure
(MAP) sensor. |
| • | Inspect for proper operation of the throttle position (TP) sensor. |
| • | Inspect for proper operation of the engine coolant temperature
(ECT) sensor. |
|
Fuel System
|
| • | Inspect the fuel filter for being plugged or restricted. |
| • | Inspect items which can cause an engine to run rich--Short
term FT is significantly in the negative range. Refer to Diagnostic Aids for
DTC P0172
. |
| • | Inspect items that can cause an engine to run lean--Short
term FT is significantly in the positive range. Refer to Diagnostic Aids
for
DTC P0171
. |
|
Ignition
System
|
| • | Inspect for proper ignition voltage output with a J 26792
Spark Tester or equivalent. |
| • | Inspect the spark plugs for the following conditions: |
| - | Improper spark plug gap |
| - | Burned electrodes or heavy deposits |
| • | If the spark plugs are fuel or oil fouled, the cause of the fouling
must be determined before replacing the spark plugs. |
| • | Inspect the ignition control module (ICM) for proper ground connection. |
| • | Inspect the ignition coils for cracks or carbon tracking. |
| • | Inspect the spark plug wires for proper resistance and condition. |
|
Additional Checks
|
| • | Inspect the exhaust system for a possible restriction: |
| - | Inspect the exhaust system for damaged or for possible collapsed
pipes. |
| - | Inspect the muffler for heat distress or for possible internal
failure. |
| • | Inspect the vacuum lines for kinks or leaks. |
| • | Inspect the generator output voltage. Repair the generator if
the output voltage is less than 11 volts or more than 16 volts. |
| • | If all procedures have been completed and no malfunctions have
been found, review and inspect the following items: |
| - | All electrical connections within the suspected circuit and/or
systems |
|
