Hesitation, Sag, Stumble

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 it's severe enough.

Preliminary Check

Refer to "Important Preliminary Checks." Testing and Inspection

Fuel System Checks

^ Check the fuel pressure. Refer to "Table A-7B." Related Tests, Information and Procedures

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

^ Check the Mass Air Flow (MAF) sensor response and accuracy.

^ Check for water contamination in the fuel.

^ Check the Evaporative Emissions (EVAP) Canister Purge system for proper operation.

Ignition System Checks

^ Check for faulty spark plug wires.

^ Check the spark plugs for the following:

- Terminal screw - bent, loose (rotate and pull)

- Ceramic Insulator - cracks, tracking, deposits (red or black dust)

- Tip Insulator - cracks, tracking, deposits (oil, carbon, glazing, fuel additive), loose (rattles)

- Center electrode - loose (wiggles side to side)

- Platinum pads - missing, wear, gap size (too large or too small)

Additional Checks

^ Check the Service Bulletins for service updates.

^ Check the generator output voltage.

^ Check the Exhaust Gas Recirculation (EGR) valve operation.