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HOMESERVICE MANUALSOLDSMOBILE2004BRAVADA AWDREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 1764 (ENGINE MECHANICAL - 4.2L)DIAGNOSTIC INFORMATION AND PROCEDURESENGINE COMPRESSION TESTTOOLS REQUIRED
2004 Oldsmobile Bravada AWD

Tools Required

2004 Oldsmobile Bravada AWDSECTION Tools Required
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J 38722  Compression Tester. See Special Tools .

A compression pressure test of the engine cylinders determines the condition of the rings, the valves, and the head gasket.

    IMPORTANT: The battery must be at or near full charge. Do not block the throttle open.
  1. Remove the air duct from the throttle control module.
  2. Remove the ignition control modules.
  3. Disable the fuel system.
  4. Remove the spark plugs.
    5. Fig 1: Measuring Engine Compression
    GM637669Courtesy of GENERAL MOTORS CORP.
  5. Measure the engine compression, using the following procedure:
    1. Firmly install J 38722  to the spark plug hole. See Special Tools .
    2. Have an assistant crank the engine through at least four compression strokes in the testing cylinder.
    3. Check and record the readings on J 38722  at each stroke. See Special Tools .
    4. Disconnect J 38722  . See Special Tools .
    5. Repeat the compression test for each cylinder.
  6. Record the compression readings from all of the cylinders. A normal reading should be approximately 1482 kPa (215 psi).

    The lowest reading should not be less than 70 percent of the highest reading.

  7. The following are examples of the possible measurements:
    • When the compression measurement is normal, the compression builds up quickly and evenly to the specified compression on each cylinder.
    • When the compression is low on the first stroke and tends to build up on the following strokes, but does not reach the normal compression, or if the compression improves considerably with the addition of three squirts of oil, the piston rings may be the cause.
    • When the compression is low on the first stroke and does not build up in the following strokes, or the addition of oil does not affect the compression, the valves may be the cause.
    • When the compression is low on two adjacent cylinders, or coolant is present in the crankcase, the head gasket may be the cause.
  8. Install the air duct to the throttle body.
  9. Install the spark plugs.
  10. Enable the fuel system.
  11. Install the ignition control modules.
RENDER: 1.0x

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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.