This tutorial will help you test the engine compression on your 3.1L V6 Buick or Oldsmobile.
I'm also going to show you how to interpret your compression test results to find out if you do have a compression problem on your hands.
All of the test steps are explained in a step-by-step manner.
Contents of this tutorial:
APPLIES TO: This tutorial applies to the following vehicles:
- 3.1L V6 Buick Century: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005.
- 3.1L V6 Buick Regal: 1994, 1995, 1996.
- 3.1L V6 Buick Skylark: 1994, 1995, 1996.
- 3.1L V6 Oldsmobile Achieva: 1994, 1995, 1996, 1997, 1998.
- 3.1L V6 Oldsmobile Cutlass: 1997, 1998, 1999.
- 3.1L V6 Oldsmobile Cutlass Ciera: 1994, 1995, 1996.
- 3.1L V6 Oldsmobile Cutlass Supreme: 1993, 1994, 1995, 1996, 1997.
Symptoms Of Low Or No Engine Compression
For the most part, engine compression problems cause two types of issues. These are:
- An engine compression issue will cause a no-start problem.
- - or -
- The engine will start and run, but it will run with a misfire or will have a rough idle.
If the engine in your 3.1L Buick or Oldsmobile starts and runs, then an engine compression problem will cause one or more of the following symptoms:
- Bad gas mileage.
- A heavier exhaust smell coming out of its tailpipe.
- Engine is not as peppy as it was once.
- Rough idle that goes away as soon as you accelerate the engine.
- Misfire trouble codes (on OBD II equipped vehicles):
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
- P0305: Cylinder #5 Misfire.
- P0306: Cylinder #6 Misfire.
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 that I have always used is the Actron CP7827 Compression Tester Kit. My only complaint about this engine compression tester is that 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’ Engine Compression Test
To test the compression on your 3.1L V6 Buick (Oldsmobile) you're going to need to remove the spark plugs.
Before you remove them, it's very important that you label each spark plug wire with the cylinder number it belongs to. This will save you the headache of losing the spark plug wires' firing order.
And of course, as you are already aware, you're going to need a compression tester. If you don't have one, you can run down to your local auto parts store (AutoZone, O'Reilly Auto Parts) and borrow one from them.
If you like to buy one and save a few bucks in the process, take a look at my recommendations here:
IMPORTANT: 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 completely. Removing the spark plugs from a hot engine can damage the spark plug hole threads in the cylinder head. This is a nightmare you want to avoid!
CAUTION: Take all necessary safety precautions. The engine has to be cranked to perform the engine compression test. Be careful and think safety all the time!
Okay, to get this pot boiling, this is what you need to do:
- 1
Disable the fuel system. You can do this by removing the fuel injector fuse(s).
This will prevent fuel from being injected into the cylinders as you crank the engine. - 2
Disable the ignition system by disconnecting the ignition coil/ignition module assembly from its electrical connector(s).
IMPORTANT: Don't overlook this step, since disabling the ignition system will prevent the ignition coil pack from firing spark during the test. - 3
Remove all 6 spark plug wires and remove all 6 spark plugs.
I recommend labeling the spark plug wires before removing them so you'll know where they go when you put them back on.
As you're removing the spark plugs, be careful and don't drop any of them on the floor, or you could cause its ceramic insulator to break, and this will cause a misfire! - 4
Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder (this is the spark plug hole closest to the drive belt).
IMPORTANT: Hand tighten the compression gauge only! Do not use any type of tool to get it tight. - 5
When the tester is set up, ask your helper to crank the engine. Your job is to keep your eye on the compression tester's gauge.
- 6
Once the needle on the gauge stops climbing, have your helper stop cranking the engine.
- 7
Write down the compression value on a piece of paper.
Include the number of the cylinder this reading belongs to. - 8
Repeat steps 3 thru' 7 on the remaining cylinders.
Let's take a look at what your test results mean:
CASE 1: Low or no compression in 2 or all 6 cylinders. This test result indicates a serious internal problem.
The most common issues would be:
- Blown head gasket.
- Broken timing chain or timing gear.
- Engine threw a rod.
CASE 2: Low compression in one or more cylinders. Up to a certain point, it's normal for the compression to vary a little between cylinders (as the engine accumulates thousands of miles).
But if these values vary too much, then you're gonna' have a bonafide misfire on your hands.
The next step is to do some math to find out if this low compression value is within a normal parameter or not. Go to: Interpreting Your Compression Test Results.
