GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2000 🢒 Century (China) 🢒 Engine 🢒 Engine Controls - 2.5L (LB8) and 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
    • Inspect the system fuel pressure. Refer to Fuel System Pressure Test .
    • Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Inspect items which can cause an engine to run rich (long term fuel trim significantly in the negative range). Refer to Diagnostic Aids in DTC P0172 Fuel Trim System Rich .
    •  Inspect items that can cause an engine to run lean (long term fuel trim significantly in the positive range). Refer to Diagnostic Aids in DTC P0171 Fuel Trim System Lean .
    •  Inspect for fuel in the fuel pressure regulator vacuum hose.

Sensor/System
  1. Inspect for conditions which cause an incorrect idle speed:
    2. • Throttle body tampering, excessive deposits or damage--Refer to Fuel Metering System Component Description .
    •  Restricted air intake system
    •  Large vacuum leak
  2. Inspect the TP sensor and related circuit wiring. Refer to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage .
  3. Inspect the EGR system for proper operation. Refer to Exhaust Gas Recirculation (EGR) System Description .
  4. Inspect the PCV valve for proper operation. Refer to Crankcase Ventilation System Description .
  5. Inspect the transaxle range switch input with the vehicle in drive and the gear selector in drive or overdrive.
  6. Inspect the following for damage:
    7. •  Bent harmonic balancer interrupter rings
    •  Damaged crankshaft position sensor

Ignition System
    • Inspect for proper ignition voltage output using the following steps:
       -  Clip the J 26792 spark tester to engine ground.
       -  Connect one end of a spark plug wire to the J 26792 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 J 26792 spark tester. A spark should be observed.
       -  Repeat the above steps for each coil.
    •  If spark is not present at the plugs, inspect for the following conditions:
       -  Inspect the coils for cracks, carbon tracking/arcing or a resistance value outside the specified range.

Coil Resistance
5K-7K ohms (5,000-7,000 ohms)

       -  Inspect the spark plug wires for 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
1 968 ohms per meter (600 ohms per foot).

    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 the spark plugs and inspect 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.
    • Inspect 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 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:
       -  Camshaft
       -  Cylinder heads
       -  Pistons, etc.
    •  Refer to Base Engine Misfire Diagnosis in Engine Mechanical.

Additional Checks
    • Inspect the exhaust system for possible restrictions:
       -  Inspect the exhaust system for damaged or collapsed pipes.
       -  Inspect the mufflers for heat distress or possible internal failure.
       -  Inspect for possible plugged three-way catalytic converter. Refer to Exhaust Leakage - Not OBD II in Engine Exhaust and 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).
    •  Inspect for intake and exhaust manifold passages for casting flash. Refer to Base Engine Misfire Diagnosis in Engine Mechanical.
    •  Inspect for faulty motor mounts. Refer to Base Engine Misfire Diagnosis in Engine Mechanical.