Surges and/or Chuggles

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 CHECKS
- Refer to Preliminary Checks. - Important Preliminary Checks
- Be sure driver understands Torque Converter Clutch (TCC) and A/C compressor operation in owner's manual.
- Use a scan tool to make sure reading of Vehicle Speed Sensor (VSS) matches vehicle speedometer except vehicles with electronic transmissions where some variation between VSS and speedometer is normal.

SENSORS
Oxygen Sensor (HO2S)
Check for silicon contamination from fuel, or use of improper sealant (never use any sealant on waterproof connectors). The sensor may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication). The control module will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem.

FUEL SYSTEM
To determine if the condition is caused by a rich or lean system, the vehicle should be driven at the speed of the complaint. Monitoring fuel trim will help identify a problem.

Lean - Long term fuel trim greater than 150. Refer to Diagnostic Charts / DTC 44 Diagnostic Aids-Lean Exhaust. Testing and Inspection

Rich - Long term fuel trim less than 115. Refer to Diagnostic Charts / DTC 45 Diagnostic Aids-Rich Exhaust. Testing and Inspection

CHECK:

- Fuel pressure while condition exists, refer to Diagnostic Charts / Chart A-6 Fuel System Diagnosis. Testing and Inspection


IGNITION SYSTEM
CHECK:

- For proper ignition voltage output voltage using spark tester J 26792 or equivalent (ST 125).
- Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.
- Ignition timing.

ADDITIONAL CHECKS
CHECK:

- Control module grounds for being clean, tight, and in their proper locations.
- Generator output voltage. Repair if less than 9 or more than 16 volts.
- Vacuum lines for kinks or leaks.
- For intermittent Exhaust Gas Recirculation (EGR).
- Torque Converter Clutch (TCC) operation.