How to Perform a Compression Test on the Engine in a Chevy Impala

Written by ehow cars editor
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The Chevy Impala returned to the market in 2000 featuring a V6 engine, but 2006 and newer models offer a choice of V6 or the more powerful V8 engine. When these engines run poorly, a compression test is a helpful tool to diagnose the problem. Tearing apart the engine is difficult and time-consuming, but performing a compression test is simple and quick.

Skill level:
Moderately Easy

Things you need

  • Compression tester
  • Motor oil

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  1. 1

    Start by warming up the engine in the Chevy Impala, since a compression test on a cold engine will be inaccurate. After shutting down the engine, disable the ignition system to avoid electrical shock.

  2. 2

    Remove all of the spark plugs. If the car has a V8 engine, there will be eight spark plugs, but if it contains a V6, there will be only six.

  3. 3

    Insert the compression tester into any of the spark plug holes. Crank the starter to rotate the engine, building compression in that cylinder. Record the compression number and move on to the next spark plug hole. Repeat the procedure until you test all six or eight cylinders and record the compression numbers.

  4. 4

    Diagnose where the problem is by comparing these compression numbers to manufacturer specifications. If the Chevy Impala is a 2006 model or newer, the compression ratio for a V6 engine is 9.8:1. If it contains a V8 engine, the ratio is 10.0:1. Older models, however, vary by horsepower. If the V6 engine has 180 hp, the ideal ratio is 9.5:1, but if it has 200 hp, the ratio is 9.4:1. Compression numbers should fall within 15 psi of the recommended ratio.

  5. 5

    Compare the compression numbers to each other. They should be no more than 10 psi apart. If any of the cylinders has a low reading, then you need to retest it.

  6. 6

    Add a capful of motor oil to the cylinder and perform the test again to see if the compression number changes. If it doesn't, the cylinder has worn valves or valve seats, but if the number increases, the cylinder has worn walls or piston rings instead.

Tips and warnings

  • The 2005 model of the Chevy Impala also offered a 240 hp V6 engine. The compression ratio for this model car is 8.5:1.

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