GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2001 🢒 Century 🢒 Engine 🢒 Engine Controls - 3.1L (LG8) 🢒 Cuts Out, Misses

Inspection/Test

Action

DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases.

Preliminary
    •  Refer to Intermittent Conditions before starting.
    •  Search for bulletins.

Fuel System
    •  Test the fuel system circuits for proper operation. Refer to Fuel Pump Electrical Circuit Diagnosis .
    •  Test for low fuel pressure. Refer to Fuel System Diagnosis .
    •  Test for faulty fuel injectors. Refer to Fuel Injector Balance Test with Special Tool , Fuel Injector Balance Test with Tech 2 , Fuel Injector Solenoid Coil Test test procedures.
    •  Inspect for fuel contamination. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    •  Inspect any items which may cause an engine to run rich, long term fuel trim is significantly in the negative range. Refer to Diagnostic Aids for DTC P0172.
    •  Inspect any items which may cause an engine to run lean, long term fuel trim is significantly in the positive range. Refer to Diagnostic Aids for DTC P0171.

Sensor/System
  1. Inspect for conditions which cause an incorrect idle speed:
    2. •  Throttle body tampering, excessive deposits, or damage. Refer to Fuel System Description .
    •  Restricted air intake system
    •  Large vacuum leak
    •  Inspect the air intake ducts for being collapsed, damaged areas, looseness, improper installation, or leaking especially between the MAF sensor and the throttle body.
  2. Inspect the throttle position (TP) sensor and related circuit wiring. Refer to DTC P0123 .
  3. Monitor the 24X crankshaft position (CKP) and camshaft position (CMP) sensors on scan tool. If both are not responding, test the sensor feed circuit. Both sensors use a separate feed circuit but are internally connected to power. Test all 24X and CMP sensor circuits for intermittents. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  4. Monitor the 3X parameter on the scan tool. If the 3X is not responding, inspect the 7X CKP sensor and circuits for intermittents. Inspect the IC circuit, bypass circuit, 3X reference high circuit, and the 3X reference low circuit for intermittents. If these circuits become open, or shorted may not set a DTC immediately, but are capable of causing driveability complaints. Refer to Testing for Intermittent Conditions and Poor Connections in Wiring Systems.
  5. Test the exhaust gas recirculation (EGR) system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
  6. Test the PCV valve for proper operation.
  7. Inspect the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive.
  8. Inspect the following for damage:
    9. •  Bent balancer interrupter rings
    •  Damaged crankshaft position sensor

Ignition System
    • Inspect for proper ignition voltage output using the following steps:
        1.  Attach the J 26792 spark tester to engine ground.
        2.  Connect the spark plug end of the spark plug wire to the J 26792 spark tester; leave the other end of the spark plug wire connected to the coil being tested.
        3.  Connect the spark plug end of the companion spark plug wire to ground.

The companion spark plug wire is the wire attached to the corresponding coil tower.

        4.  Crank the engine while observing the J 26792 spark tester; a spark should be observed.
        5.  Repeat the above steps for each coil.
    •  If spark is not present at the coils, inspect for the following conditions:
       -  Coils--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000-8000ohms (5K-8Kohms)

       -  Spark Plug wires--signs of arcing, cross firing, cracks, carbon tracking, plug boot damage, pinched, improper routing, or a resistance value outside the specified range.

Spark Plug Wire Resistance
3000ohms per foot (1 9686ohms per meter).

    Important: :  Spraying the secondary ignition wires with a light mist of water may help locate an intermittent problem. Ignition voltage will arc to ground when a secondary component is faulty.

       -  Defective ignition module.
       -  Ignition system wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    •  Remove spark plugs and inspect for the following conditions:
       -  Fouled plugs
       -  Cracks
       -  Wear
       -  Improper gap
       -  Burned or damaged electrodes
       -  Improper heat range or reach
    •  If spark plugs are gas or oil fouled, the cause of the fouling must be determined before replacing the spark plugs. Refer to Spark Plug Inspection .

Engine Mechanical
    •  Inspect engine mechanical for the following conditions:
       -  Test the compression--Refer to Engine Compression Test in Engine Mechanical.
       -  Sticking or leaking valves
       -  Worn camshaft lobes
       -  Valve timing
       -  Bent push rods
       -  Worn rocker arms
       -  Broken valve springs
       -  Excessive oil in combustion chamber--Leaking valve seals
       -  Low cylinder compression
    •  For incorrect basic engine parts--Inspect the following components:
       -  Camshaft
       -  Cylinder heads
       -  Pistons, etc.
    •  Refer to Symptoms - Engine Mechanical in Engine Mechanical.

Additional
    • Inspect the exhaust system for possible restrictions:
       -  Inspect exhaust system for damaged or collapsed pipes.
       -  Inspect mufflers for heat distress or possible internal failure.
       -  For possible plugged catalytic converter.
    •  An engine miss condition can be caused by electromagnetic interference (EMI) on the reference circuit. EMI can usually be detected by monitoring engine RPM with a scan tool. A sudden increase in RPM with little change in actual engine RPM change, indicates EMI is present. If a problem exists, inspect routing of secondary ignition wires, high voltage components, near the ignition control circuits.