Hesitation, Sag, Stumble

DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at all vehicle speeds. Usually most severe when first trying to make the vehicle move, as from a stop sign. May cause engine to stall if severe enough.



PRELIMINARY CHECKS

^ Perform the careful visual/physical checks as described at start of "Preliminary Checks."

^ CHECK: For correct EPROM. (See Service Bulletins.)
^ CHECK: Service Bulletin for updates.
^ CHECK: EGR operation, use CHART C-7. Chart C-7 EGR System Check

SENSORS

^ CHECK: TP sensor - Check TP sensor for binding or sticking. Voltage should increase at a steady rate as throttle is moved toward Wide Open Throttle (WOT).
^ CHECK: MAP sensor - use CHART C-1D. Chart C-1D Manifold Absolute Pressure (MAP) Output Check

IGNITION SYSTEM

^ CHECK: Spark plugs for being fouled.
^ CHECK: Ignition system ground.

FUEL SYSTEM

^ CHECK: Fuel pressure, use CHART A-7. Related Tests, Information and Procedures
^ CHECK: For contaminated fuel.
^ CHECK: Evaporative Emission (EVAP) control system for proper operation. Use CHART C-3. Chart C-3 Evaporative Emission Control System
^ CHECK: Fuel injectors. Perform "Injector Balance Test," use CHART C-2A. Part 3 of 3 (Fuel Injector Balance Test)

ADDITIONAL CHECKS

^ CHECK: Engine thermostat functioning correctly and proper heat range.
^ CHECK: Generator output voltage. Repair if less than 9 or more than 16 volts.
^ CHECK: For intake valve deposits.