Cuts Out, Misses. Buick GL7 (Export) 2000

For 1990-2009 cars

Inspection/Test | Action
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DEFINITION: Steady pulsation or jerking that follows engine speed, usually more pronounced as engine load increases.

Preliminary

• | Refer to Powertrain On Board Diagnostic (OBD) System Check .

• | Refer to Intermittent Conditions .

• | Search for bulletins.

Fuel System

• | Test the system fuel pressure. Refer to Fuel System Pressure Test .

• | Test the injectors. Refer to the following procedures:

- | Fuel Injector Balance Test

- | Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Between 10-35 Degrees C (50-95 Degrees F)

- | Fuel Injector Solenoid Coil Test - Engine Coolant Temperature Outside 10-35 Degrees C (50-95 Degrees F)

• | Inspect for contaminated fuel. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .

• | Inspect any items which may cause an engine to run rich, long term fuel trim 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 significantly in the positive range. Refer to Diagnostic Aids for DTC P0171.

• | Inspect for fuel in the fuel pressure regulator vacuum hose.

Sensor/System

1. Inspect for conditions which cause an incorrect idle speed:

• | Any throttle body tampering, excessive deposits, or damage. Refer to Fuel Metering System Component Description .

• | A restricted air intake system

• | A large vacuum leak

2. Inspect the TP sensor and the related circuit wiring. Refer to DTC P0123 Throttle Position (TP) Sensor Circuit High Voltage .
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.
6. Test the PCV valve for proper operation.
7. Inspect the Transaxle Internal Mode Switch input with the vehicle in drive and the gear selector in drive or overdrive.
8. Inspect the following for damage:

• | Bent harmonic 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
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 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.

Engine Mechanical

• | Check the following engine mechanical concerns:

- | The compression

- | Sticking or leaking valves

- | Worn camshaft lobes

- | Valve timing

- | Bent push rods

- | Worn rocker arms

- | Broken valve springs

- | Excessive oil in combustion chamber and leaking valve seals

- | A low cylinder compression

• | Inspect the following components for incorrect basic engine parts. Refer to Base Engine Misfire Diagnosis in Engine Mechanical:

- | The camshaft

- | The cylinder heads

- | The pistons, etc.

Additional Checks

• | Inspect the exhaust system for restrictions. Refer to Restricted Exhaust System Check :

- | Inspect the exhaust system for damaged or collapsed pipes.

- | Inspect the mufflers for heat distress or internal failure.

- | Inspect for a plugged 3-way catalytic converter.

• | 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 in RPM with little change in the actual engine RPM indicates EMI is present. If a problem exists, check the routing of the secondary ignition wires near high voltage components and ignition control circuits.

• | Inspect the 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.