GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 1999 🢒 Century (China) (CNG) 🢒 Engine 🢒 Engine Controls - 3.0L (L46) 🢒 Cuts Out, Misses

Checks

Action

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

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

Fuel System
    • Check system fuel pressure. Refer to Fuel System Pressure Test .
    •  Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis Testing.
    •  Check items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids for DTC P0172.
    •  Check items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids for DTC P0171.
    •  Check for fuel in the Fuel Pressure Regulator vacuum hose.

Sensor/System
    • Check for conditions which cause an incorrect idle speed.
       - Throttle body tampering, excessive deposits, or damage.
       - Restricted air intake system. Refer to Air Intake System Description .
       -  Large vacuum leak.
    •  Check the TP Sensor and related circuit wiring. Refer to DTC P0123 Diagnosis.
    •  Check the EGR system for proper operation.
    •  Check the PCV Valve for proper operation.
    •  Check the Transaxle Range Switch input with the vehicle in drive and the gear selector in drive or overdrive. Refer to Transaxle Range Switch Valid Combinations.
    •  Check the following for damage:
      •  Bent harmonic balancer interrupter rings.
      •  Damaged Crankshaft Position Sensor.

Ignition System
    • Check for proper ignition voltage output using the following steps:
       -  Clip the spark tester J 26792 to engine ground.
       -  Connect one end of a spark plug wire to the spark tester, leave the other end of the spark plug wire to the coil being tested.
       -  Connect one end of another spark plug wire to the other coil tower; connect the other end of the spark plug wire to ground.
       -  Crank the engine while observing the spark tester; a crisp blue spark should be observed.
       -  Repeat the above steps for each coil.
    •  If adequate spark is not present at the coil(s), check for the following conditions:
       -  Coil(s)--Cracks, carbon tracking/arcing, or a resistance value outside the specified range.

Coil Resistance
5000-7000ohms (5K-7Kohms)

       -  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
600ohms per foot (1 968ohms per meter).

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

       -  Defective module.
       -  Ignition System Wiring--Loose ignition module feed or ground connection, or damaged system wiring.
    •  Remove spark plugs and check for the following:
       -  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.
    •  Check for the following intermittent ignition system conditions:
       -  Intermittent CKP 24X Signal.
       -  Intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position sensor.
       -  Intermittent 3X reference signal.
       -  Intermittent camshaft position signal

Engine Mechanical
    • Check engine mechanical for the following:
       -  Check compression.
       -  Sticking or leaking valves.
       -  Worn camshaft lobe(s).
       -  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:
       -  Camshaft
       -  Cylinder heads
       -  Pistons, etc.
    •  Refer to Engine Mechanical for diagnosis procedures.

Additional Checks
    • Check exhaust system for possible restrictions. Check for the following:
       -  Inspect exhaust system for damaged or collapsed pipes.
       -  Inspect mufflers for heat distress or possible internal failure.
       -  For possible plugged Three-Way catalytic converter. Refer to Restricted Exhaust System Check .
    •  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, check routing of secondary ignition wires, high voltage components (Near Ignition Control circuits).
    • Check for intake and exhaust manifold passages for casting flash. Refer to Engine Mechanical.
    •  Check for faulty motor mounts. Refer to Engine Mechanical.