Hesitation, Sag, Stumble. GMC Truck Jimmy

For 1990-2009 cars only

Makes 🢒 GMC_Truck 🢒 1999 🢒 Jimmy - 4WD 🢒 Engine 🢒 Engine Controls - 4.3L 🢒 Hesitation, Sag, Stumble

Checks

Action

DEFINITION: The vehicle has a momentary lack of response when depressing 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 it's severe enough.

Preliminary Check

Refer to Symptoms .

Fuel System Checks

•	Check the fuel pressure. Refer to Fuel System Diagnosis .

•	Check the Throttle Position (TP) sensor for binding or sticking. Voltage should increase at a steady rate as the throttle moves toward Wide Open Throttle (WOT).

•	Check the Manifold Absolute Pressure (MAP) sensor response and accuracy.

•	Check for water contamination in the fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

•	Check the Canister Purge system for proper operation

•	Perform the fuel injector coil test. Refer to Fuel Injector Solenoid Coil Test .

•	Perform the fuel injector balance test. Refer to Fuel Injector Balance Test with Tech 2 .

•	Check for low fuel pressure after a cold start or during a moderate or full throttle acceleration.

Ignition System Checks

•	Check for damaged spark plug wires.

•	Check for fouled spark plugs.

•	Check for proper ignition system performance. Refer to Enhanced Ignition System Diagnosis .

Additional Checks

•	Check the Service Bulletins for calibration updates.

•	Check the generator output voltage. Refer to Charging System Check in Engine Electrical.

•	Check the EGR Valve operation. Refer to Exhaust Gas Recirculation (EGR) System Diagnosis .

•	Check for a restricted exhaust. Refer to Restricted Exhaust System Check .