GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 Buick 🢒 2002 🢒 LeSabre 🢒 Engine 🢒 Engine Controls - 3.8L 🢒 Cuts Out, Misses

Checks

Action

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

Preliminary
    • Refer to Important Preliminary Checks Before Starting in Symptoms - Engine Controls .
    • Refer to Visual/Physical Check in Symptoms - Engine Controls .
    • Search for bulletins.

Fuel System
    • Check the fuel pressure.
        Refer to Fuel System Diagnosis .
    • Check the fuel injectors. Refer to Fuel Injector Solenoid Coil Test .
    • Check for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
    • Check the items which can cause an engine to run rich. Refer to DTC P0172 .
    • Check the items that can cause an engine to run lean. Refer to DTC P0171 .
    • Check for fuel in the fuel pressure regulator vacuum hose. If fuel is present, replace the fuel pressure regulator. Refer to Fuel Pressure Regulator Replacement .

Sensor/System
    • Check for any conditions which cause an incorrect idle speed:
       - Throttle body tampering, excessive deposits, or damage.
       - A restricted air intake duct or a dirty air cleaner element. Refer to Air Cleaner Element Replacement .
       - Check for a large vacuum leak.
    • Check the throttle position (TP) sensor and the related circuit wiring. Refer to DTC P0123 .
    • Check the EGR system:
       - Inspect the EGR pipes and the adapter for vacuum leaks.
       - Remove the EGR valve and check for a sticking pintle. Refer to Exhaust Gas Recirculation Valve Replacement .
    • Check the PCV valve for proper installation.
    • 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 table in Range Reference .
    • Check for the following conditions:
       - Check for a bent harmonic balancer interrupter rings.
       - Check for a damaged crankshaft position sensor.

Ignition System
    • Check 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 . Connect the other end of the spark plug wire to the coil being tested.
       - Connect another spark plug wire between the remaining tower of the coil being tested and ground.
       - Crank the engine while observing the J 26792 . A spark should be observed.
       - Repeat the above steps for each coil.
    • If spark is not present at the plugs, check for the following conditions:

   Important: If carbon tracking is detected on a component, replace that component and the component's mate.

       - Inspect the coils for cracks, carbon tracking/arcing, or a secondary resistance value outside the specified range.

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

       - Inspect the spark plug wires for signs of arcing/cross firing, cracks, carbon tracking, plug boot damage, pinched, incorrect routing, or a resistance value more than the specified value.

Spark Plug Wires Resistance
1000-1500 ohms/ft

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

       - Check for a malfunctioning ignition control module.
       - Check the ignition system wiring for a loose ignition module feed, ground connection, or damaged system wiring.
    • Remove the spark plugs.
    • Inspect the spark plugs for the following conditions:

   Important: If carbon tracking is detected on any component, replace that component and it's mate.

       - Check the spark plugs for carbon tracking on the porcelain and pitting on the plug wire contact.
       - Check the spark plugs for fouling.
       - Check the spark plugs for cracks.
       - Check the spark plugs for incorrect gap.
       - Check the spark plugs for burned or damaged electrodes.
       - Check the spark plugs for incorrect heat range. Refer to Maintenance Items .
    • 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:
       - Check for an intermittent crankshaft position (CKP) sensor Sync or 18X signal.
       - Check for an intermittent ignition feed circuit or sensor ground circuit to the crankshaft position sensor or the camshaft position (CMP) sensor.
       - Check for a intermittent 3X reference signal.
       - Check for a intermittent CMP signal

Engine Mechanical
    • Check engine mechanical for the following:
       - Check the compression.
       - Check for sticking or leaking valves.
       - Check for worn camshaft lobes.
       - Check the valve timing.
       - Check for bent push rods.
       - Check for worn rocker arms.
       - Check for broken valve springs.
       - Check for excess oil in combustion chamber--Inspect for leaking valve seals.
       - Check for low cylinder compression.
    • Refer to the appropriate misfire procedures in Engine Mechanical. Inspect for incorrect engine parts, such as the following basic components:
       - The camshaft
       - The cylinder heads
       - The pistons, etc.

Additional Checks
    • Check the exhaust system for a restriction. Refer to Restricted Exhaust .
       - Inspect the exhaust system for damaged or collapsed pipes. Refer to Exhaust Leakage .
       - Inspect mufflers for heat distress or an internal failure.
       - Check for a plugged three-way catalytic converter. Refer to Restricted Exhaust .
    •  An engine miss condition can be caused by electromagnetic interference (EMI) on the reference circuit. EMI can usually be detected by monitoring the engine RPM with a scan tool. A sudden increase or decrease in the RPM with little change in the actual engine RPM indicates that EMI is present. Check the routing of secondary ignition wires. Also, check the ignition coils for cracks, carbon tracking, or signs of arcing.
    • Check the intake and exhaust manifold passages for casting flash.
    • Check for loose, worn, or broken motor mounts. Refer to Engine Mount Inspection .