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 accelerator pedal.

PRELIMINARY CHECKS
Perform the "Visual and Physical Checks" as described in Preliminary Checks. Be sure driver understands A/C compressor operation in owner's manual. Testing and Inspection

SENSORS
CHECK: Heated Oxygen Sensor (HO2S) for silicon contamination from fuel, or use of improper RTV sealant. The HO2S may have a white, powdery coating and result in a high but false signal voltage (rich exhaust indication). The Engine Control Module (ECM) will then reduce the amount of fuel delivered to the engine, causing a severe driveability malfunction.

FUEL SYSTEM

NOTICE: To determine if the condition is caused by a rich or lean system, the vehicle should be driven at the speed of the complaint. Using a Tech 1 scan tool to monitor HO2S voltage will help identify a malfunction.

Lean - HO2S voltage below 450 mV.
Rich - HO2S voltage above 450 mV.

CHECK: Fuel pressure while condition exists.
CHECK: In-line fuel filter. Replace if dirty or plugged.

IGNITION SYSTEM
CHECK: For proper ignition output voltage using J 26792 or equivalent
CHECK: Spark plugs. Remove spark plugs, check for wet plugs, cracks, wear, improper gap, burned electrodes, or heavy deposits. Repair or replace as necessary.

ADDITIONAL CHECKS
CHECK: ECM grounds for being clean, tight, and in their proper locations.
CHECK: Generator output voltage.
CHECK: Vacuum hoses for kinks or leaks.
CHECK: For intermittent Exhaust Gas Recirculation (EGR) at idle.
CHECK: Speedometer for correct operation (fluctuating needle, speedometer cable for restricted movement, damaged cable).