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HOMESERVICE MANUALSCHEVROLET2001CHEVY EXPRESS G2500, VAN PASSENGER EXTENDED, 5.0 MREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 869 (ENGINE MECHANICAL - 8.1L - SERVICE, REPAIR AND DIAGNOSTICS)DIAGNOSTIC INFORMATION AND PROCEDURESENGINE COMPRESSION TEST
2001 Chevrolet Chevy Express G2500, Van Passenger Extended, 5.0 M

Engine Compression Test

2001 Chevrolet Chevy Express G2500, Van Passenger Extended, 5.0 MSECTION Engine Compression Test
WARNING: This page does not describe the selected car, but rather 8 other vehicles, including the 2001 GMC Yukon XL, 2001 GMC Sierra, 2001 GMC Cab & Chassis Sierra, 2001 GMC C3500 HD, and 2001 Chevrolet Suburban. However, it is still accessible from the selected car via links, so may be relevant.
  1. Disconnect the ignition coil wire harness connector at the front of the engine on the left cylinder bank and at the rear of the engine at the right cylinder bank.
  2. Disconnect the fuel injector electrical harness connector at the rear of the intake manifold.
  3. Remove all spark plugs.
  4. Block the throttle plate wide open.
  5. Charge the battery, if the battery is not fully charged.
  6. Start with the compression gauge at 0, then crank the engine through 4 compression strokes, 4 puffs.
  7. Make the compression test the same for each cylinder. Record the reading.

    The minimum compression in any 1 cylinder should not be less than 70 percent of the highest cylinder. No cylinder should read less than 690 kPa (100 psi). For example, if the highest pressure in any 1 cylinder is 1 035 kPa (150 psi), the lowest allowable pressure for any other cylinder would be 725 kPa (105 psi), (1035 x 70% = 725) (150 x 70% = 105).

  8. If some cylinders have low compression, inject approximately 15 ml (1 tablespoon) of engine oil into the combustion chamber through the spark plug hole.
    • Normal - Compression builds up quickly and evenly to the specified compression for each cylinder.
    • Piston Rings Leaking - Compression is low on the first stroke, then compression builds up with the following strokes, but does not reach normal. Compression improves considerably when you add oil.
    • Valves Leaking - Compression is low on the first stroke. Compression usually does not build up on the following strokes. Compression does not improve much when you add oil.
    • If 2 adjacent cylinders have lower than normal compression, and injecting oil into the cylinders does not increase the compression, the cause may be a head gasket leaking between the 2 cylinders.
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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.