Checks
| Action
|
DEFINITION: The engine has a power variation under a steady throttle
or cruise. The vehicle feels as if it speeds up and slows down with no change
in the accelerator pedal.
|
Preliminary Checks
|
| • | Search for service bulletins. |
| • | Verify that the operator understands the torque converter clutch
operation. |
| • | Verify that the operator understands the A/C compressor operation. |
| • | Use the scan tool to verify the reading of the vehicle speed sensor
(VSS). It should match the vehicle's speedometer. |
| • | Inspect the control module grounds. The grounds should be clean,
tight and in their proper locations. |
|
Sensor Checks
|
| • | Inspect the oxygen sensor (O2S) for contamination and performance. |
| • | Verify proper operation of the TP sensor. |
| • | Verify proper operation of the MAP sensor. |
| • | Verify proper operation of the ECT sensor. |
| • | Inspect the EGR valve for a stuck open pintle. |
|
Fuel System Checks
|
| • | Inspect for a rich or lean symptom that causes the condition.
Drive the vehicle at the speed of the complaint. Monitoring the oxygen sensors
will help to identify the problem. |
| • | Verify that the CNG manual shut-off valve is fully open. |
| • | Inspect the high pressure regulator (HPR) filter for restrictions. |
|
Ignition System Checks
| CNG is a gaseous fuel. It requires higher secondary ignition system
voltages for the equivalent gasoline operating conditions. If a problem
is reported during CNG operation but not during gasoline operation, do
not discount the possibility of a CNG-only ignition system failure. Test
the system accordingly.
| • | Verify the proper ignition output voltage using the J 26792
or the equivalent. |
| • | Inspect the spark plugs. Remove the plugs and inspect them for
the following conditions: |
| - | Cracks on the spark plugs |
| - | Improper spark plug gap |
| • | Inspect the spark plug wires for proper resistance and condition. |
| • | Inspect the ignition coils for cracks or carbon tracking. |
| • | Inspect for loose ignition coil connections. |
| • | Inspect for loose engine control module grounds. |
| • | Inspect for loose ignition control module grounds. |
|
Additional Checks
|
| • | Verify the generator output voltage. |
| • | Inspect the vacuum hoses for kinks or leaks. Refer to the Vehicle
Emission Control Information Label. |
| • | Inspect the exhaust system for possible restrictions or any of
the following conditions: |
| - | Inspect the exhaust system for damaged or collapsed pipes. |
| - | Inspect the muffler for signs of heat distress or for a possible
internal failure. |
| - | Inspect for a possible plugged catalytic converter. Refer to Restricted
Exhaust System Check in Engine Controls - 2.2L in the J Platform Service
Manual. |
| • | Verify proper torque converter clutch (TCC) operation. Refer to
Torque Converter Clutch Diagnosis in Automatic Transaxle - 3T40 or Automatic
Transaxle 4T40-E in the J Platform Service Manual. |
If all the procedures have been completed and no malfunction has been
found, review and inspect the following items:
| • | Visually and physically inspect all the electrical connections
within the suspected circuits and systems. |
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