Surges/Chuggles

SYMPTOM 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 Diagnostic Notes. Initial Inspection and Diagnostic Overview
^ 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 VSS matches vehicle speedometer except vehicles with electronic transmissions where some variation between VSS and speedometer is normal. Refer to "DTC 16 Diagnostic Aids." DTC 16

SENSORS
Check:
^ Oxygen Sensor (O2S) 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
Check:
^ 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 "DTC 44 Diagnostic Aids." Powertrain Controls - ECM/PCM
^ Rich - Long term fuel trim less than 115. Refer to "DTC 45 Diagnostic Aids." Powertrain Controls - ECM/PCM
^ Fuel pressure while condition exists, refer to "Chart A-6." Related Tests, Information and Procedures

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 EGR.
^ TCC operation.