GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 6.5L (L57) 🢒 Hesitation, Sag, Stumble

Hesitation, Sag, Stumble EFI

Checks

Action

Definition: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall, if severe enough.

Preliminary Check

Refer to Symptoms .

Fuel System Checks
    • Check the fuel pressure. Refer to Fuel Supply System Check .
    • Check for water contamination in the fuel. Refer to Contamination Testing .
    • Check for a low fuel pressure after a cold start or during a moderate or a full throttle acceleration. If the fuel pressure drops below specification, there is possibly a malfunctioning fuel pump or a restriction in the fuel system. Refer to Fuel Supply System Check .

Additional Checks

Check the Service Bulletins for any control module software updates.

Hesitation, Sag, Stumble MFI

Checks

Action

Definition: The vehicle has a momentary lack of response when pushing down on the accelerator. The condition can occur at any vehicle speed. The condition is usually most severe when trying to make the vehicle move, as from a stop sign. The condition may cause the engine to stall, if severe enough.

Preliminary Check

Refer to Symptoms .

Fuel System Checks
    • Check the fuel pressure. Refer to Fuel Supply System Check .
    • Check for water contamination in the fuel. Refer to Contamination Testing .
    • Check for a low fuel pressure after a cold start or during a moderate or a full throttle acceleration. If the fuel pressure drops below specification, there is possibly a malfunctioning fuel pump or a restriction in the fuel system. Refer to Fuel Supply System Check .

Additional Checks

Check the Service Bulletins for any control module software updates.