Surges/Chuggles

DEFINITION
Engine power variation under steady throttle or cruise. Feels like the vehicle speeds up and slows down with no change in the acceleration pedal.

PRELIMINARY CHECKS
- Perform the careful visual checks.
- Be sure driver understands transmission [1][2]torque converter clutch, and A/C compressor operation as explained in the owners manual.

SENSORS
- Check: Heated Oxygen Sensor (HO2S). The heated oxygen sensor should respond quickly to different throttle positions; if it does not, check the heated oxygen sensor for silicon or other contaminants from fuel or use of improper RTV sealant.

The sensor may have a white, powdery coating and a high but false signal voltage (rich exhaust indication). The Powertrain Control Module (PCM) will then reduce the amount of fuel delivered to the engine, causing a severe driveability problem. Also, watch for green glycol contamination or cracking.

FUEL SYSTEM

NOTE: 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 long term fuel trim and short term fuel trim will help identify a problem. Refer to System Diagnosis/Procedures/Scan-Tool Diagnostics/Tech-1 Data Definitions, for an explanation of long and short term fuel trim.
A poor PCM ground at the ignition control module mounting bracket may cause the short term fuel trim to read about 160.

- Check: Fuel pressure while condition exists. Refer to System Diagnosis/Diagnostic Charts/A Charts/Chart A-7, Fuel System Pressure Test. Related Tests, Information and Procedures

- Check: In-line fuel filter. Replace if restricted, dirty or plugged.

IGNITION SYSTEM
- Check: For adequate ignition voltage output using spark tester J 26792 (ST-125) or equivalent Test one spark plug wire at a time.
- Check: Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary Also, check condition of spark plug wires.

ADDITIONAL CHECKS
- Check: PCM grounds for being clean, tight and in their proper location
- Check: Vacuum lines for kinks or teaks.
- Check: Generator output voltage. Repair if less than 9 or more than 17 volts.
- Check: Speedometer reading and the speed displayed on a Tech 1 scanner should be equal.