Hesitation, Sag, Stumble. Buick Roadmaster 1996

For 1990-2009 cars

Checks | Action
--- | ---
DEFINITION: Momentary lack of response as the accelerator is pushed down. Can occur at any vehicle speed. Usually more pronounced when first trying to make the vehicle move, as from a stop sign. May cause the engine to stall if severe enough.

Preliminary

• | Refer to Symptoms , Important Preliminary Checks Before Starting.

• | Search for bulletins.

• | Check PCM grounds for being clean, tight and in their proper locations. Refer to PCM wiring diagrams in Electrical Diagnosis.

Sensor/System

• | Check MAP sensor operation.

• | Check EGR for being loose or for a faulty gasket. Check EGR operation for being open all the time.

• | Using a Scan Tool, monitor TP sensor voltage. The TP sensor voltage should be less then 0.9 volt. If the TP sensor voltage is greater than 0.9 volt, inspect the ASR/TCS adjuster assembly (If so equipped). Also inspect throttle body and accelerator cables for binding. Refer to Adjuster Assembly Throttle And Cruise Control Cables.

• | Check the EGR system for proper operation.

Fuel System

• | Check for low fuel pressure. Refer to Fuel System Diagnosis .

• | Check for restricted fuel filter. Refer to Fuel System Diagnosis .

• | Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Test .

• | Check injector fuse(s) (Except F car) for being open. An open injector fuse will cause the injectors not to operate. Replace fuse and inspect injector circuits for an intermittent short to ground.

• | Perform injector balance test. Refer to Fuel Injector Balance Test for procedure.

• | Check items which can cause an engine to run rich (long term fuel trim near -14%). For a Rich condition, refer to DTC P0132 HO2S Circuit High Voltage Bank 1 Sensor 1 and DTC P0152 HO2S Circuit High Voltage Bank 2 Sensor 1 .

• | Check items that can cause an engine to run lean (long term fuel trim near 22%). For a Lean condition, refer to DTC P0131 HO2S Circuit Low Voltage Bank 1 Sensor 1 and DTC P0151 HO2S Circuit Low Voltage Bank 2 Sensor 1 .

Ignition System

• | Wetting down the secondary ignition system with water from a spray bottle may help locate damaged or deteriorated components. Look/listen for arcing or misfiring as water is applied.

• | Check for proper ignition voltage output with spark tester J 26792. Refer to Distributor Ignition (DI) System Check for procedure.

• | Remove spark plugs and check for the following:

- | Wet plugs

- | Cracks

- | Wear

- | Improper gap

- | Burned electrodes

- | Heavy deposits

• | An improper spark plug gap will cause a driveability problem. Refer to spark plug gap specification in Section OB. The spark plug gapping should be done using a wire gauge gap tool (J 41319). Refer to Spark Plug Replacement. If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to DTC P0172 Fuel Trim System Rich Bank 1 and DTC P0175 Fuel Trim System Rich Bank 2 to determine the Rich condition or Engine Mechanical for the oil fouling condition.

• | Check for loose ignition coil ground. Refer to Distributor Ignition (DI) System Check .

• | Spark plugs for proper heat range. Refer to Owners Manual or Section OB.

• | Check distributor vent system for being restricted or open. Refer to Distributor Vent System Check .

Engine Cooling System

• | Check the engine thermostat for functioning correctly and for proper heat range. Refer to Engine Cooling.

Additional Checks

• | Check generator output voltage. Refer to Engine Electrical for procedure. Repair if less than 9 or more than 16 volts.

• | An EGR valve that is excessively coked, could cause an engine misfire. Remove the EGR valve and clean as necessary. Refer to Exhaust Gas Recirculation Valve Replacement .