Poor Fuel Economy. Buick GL7 (Export) 2000

For 1990-2009 cars

Inspection/Test | Action
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DEFINITION: Fuel economy, as measured by an actual road test is noticeably lower than expected. Also, economy is noticeably lower than at one time, as previously shown by an actual road test.

Preliminary

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

• | Refer to Intermittent Conditions .

• | Search for bulletins.

• | Observe the owners driving habits:

- | Is the A/C ON full time (defroster mode ON)?

- | Are the tires at the correct pressure?

- | Are excessively heavy loads being carried?

- | Is the acceleration too much, too often?

Fuel System

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

• | Test the fuel 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)

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

• | Ensure each injector harness is connected to the correct injector and cylinder.

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

Sensor/System

• | Inspect for 24X crankshaft position (CKP) and camshaft position (CMP) sensors on the scan tool. If both are not responding, inspect the sensor feed circuit.

• | Inspect the air intake system and the crankcase for air leaks.

• | Test for proper calibration of the speedometer. Connect the J 33431-B signal generator to the VSS electrical connector. Turn the ignition and the tester on and monitor the speedometer.

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 Cooling System

• | Inspect for the proper engine coolant level.

• | Inspect for an incorrect or faulty engine thermostat. Refer to Thermostat Diagnosis in Engine Cooling.

Engine Mechanical

• | Check for the following engine mechanical concerns:

- | Check the compression

- | Sticking or leaking valves

- | Worn camshaft lobes

- | Valve timing

- | Bent push rods

- | Worn rocker arms

- | Broken valve springs

- | Excessive oil in the combustion chambers and leaking valve seals

• | 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

• | Inspect the TCC operation. Refer to Torque Converter Diagnosis in Automatic Transaxle-4T65-E.

• | Inspect the exhaust system for restrictions.

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

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

- | Inspect for catalytic converter.