How To Test Engine Compression (2002-2004 4.2L Oldsmobile Bravada, 2004-2007 4.2L Buick Rainier)

How To Test Engine Compression (2002, 2003, 2004, 2005, 2006, 2007 4.2L Oldsmobile Bravada And Buick Rainier)

Testing the head gasket on the 4.2L Oldsmobile Bravada (Buick Rainier) is not difficult.

In this tutorial, I'll explain how to perform the four most common blown head gasket tests step-by-step.

With your test results, you'll quickly determine if a blown head gasket issue is causing an engine no-start problem or an overheating problem.

APPLIES TO: This tutorial applies to the following vehicles:

  • 4.2L L6 Buick Rainier: 2004, 2005, 2006, 2007.
  • 4.2L L6 Oldsmobile Bravada: 2002, 2003, 2004.

Important Tips And Suggestions

TIP 1: Do not remove the spark plugs from a hot engine.

If the engine has been running for any length of time, let it cool down for at least an hour before attempting to remove the spark plugs.

Attempting to remove the spark plugs from a hot engine can damage the threads in the spark plug holes. This is a nightmare you want to avoid.

TIP 2: If you find the spark plugs are swimming in engine oil, as you are removing them from their spark plug tubes, you'll need to replace the valve cover gasket.

If the spark plugs are soaked in engine oil, it's important to replace them with new ones.

If the spark plug boots (that connect ignition coils to the spark plugs) are soaked in engine oil, it's important you replace them too.

TIP 3: Take all safety precautions since you'll be working around a cranking engine.

Which Compression Tester Should I Buy?

There are lot of engine compression testers to choose from and many places to buy them. I'm gonna' make two recommendations to you:

1) Which one to buy:  The engine compression tester I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is it does not come with a case to store it in.

2) Where to buy:  You can buy an engine compression tester just about anywhere, but you'll end up paying more for it (especially at your local auto parts store). The above links will help you comparison shop. I think you'll agree it's the better way to save money on the compression tester!

TEST 1: Dry Compression Test

Dry Compression Test. How To Test Engine Compression (2002, 2003, 2004, 2005, 2006, 2007 4.2L Oldsmobile Bravada And Buick Rainier)

I recommend you test the compression of all six cylinders. Once you obtain your compression test results, you'll interpret them in the next section.

If you don't have a compression tester, you can borrow one from your local auto parts store (AutoZone or O'Reilly's Auto Parts) or you can buy one.

You can check out my compression tester recommendations here: Which Compression Tester Should I Buy?.

Let's get testing:

  1. 1

    Remove the ignition coils.

  2. 2

    Remove the spark plugs.

    When removing the spark plugs, be careful not to drop any of them on the floor, or you run the risk of having the spark plug's porcelain insulator crack (causing a misfire problem).

  3. 3

    Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder.

    Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

  4. 4

    Have your helper crank the engine till the needle on the compression gauge stops climbing.

  5. 5

    Record the value at which the needle stopped and the number of the engine cylinder on a piece of paper.

  6. 6

    Repeat steps 3-5 on the remaining cylinders.

Let's take a look at what your compression test results mean:

CASE 1: You got 0 PSI in the majority of the cylinders. This tells you your Chevy Bravada or Buick Rainier's engine has serious internal problems. This is usually due to:

  • Busted timing chain.
  • Engine threw a rod.

Any compression value below 100 PSI (even if it's not 0 PSI) means internal mechanical engine trouble.

CASE 2: All cylinders have compression, but their values are not the same. It's normal for each cylinder's compression value to vary slightly from one another. But if they vary too much, you'll have a bonafide misfire or rough idle condition on your hands.

To find out, the next step is to go to: Interpreting The Compression Test Results.

Buick Vehicles:

  • Rainier 4.2L
    • 2004, 2005, 2006, 2007

Oldsmobile Vehicles:

  • Bravada 4.2L
    • 2002, 2003, 2004