This tutorial will help you test the engine compression on your 2.8L V6 S10 Pickup (GMC S15 pickup, GMC Sonoma) or 2.8L S10 Blazer.
It'll also help you to further narrow down the problem, if you do find low compression in one or more cylinders, to either the cylinder head valves or the engine piston compression rings with a 'wet' compression test.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (2.8L V6 GM) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following vehicles:
- 2.8L Chevrolet S10 Pickup: 1988, 1989, 1990, 1991, 1992, 1993.
- 2.8L GMC S15 Pickup: 1988, 1989, 1990.
- 2.8L GMC Sonoma: 1991, 1992, 1993.
This tutorial also applies to the 2.8L Chevy S10 Blazer, 2.8L GMC S15 Jimmy. See the 'Applies To' box on the left column (desktop) or at the bottom of the page (mobile device) for more info.
Important Tips And Suggestions
TIP 1: If your 2.8L equipped GM S10 pickup (Blazer) starts and runs, it's standard procedure to do the compression test with a slightly warmed up engine. The key words here are 'slightly warmed up engine' since the engine should not be hot.
To slightly warm up the engine, start her up (from a completely cold condition) and let her run for no more than 10 to 12 minutes.
TIP 2: You'll be working near a cranking engine when performing the engine compression test, so take all necessary safety precautions. Be careful and always keep safety in mind.
TIP 3: Never remove the spark plugs with a hot engine. This is important because you could strip the spark plug hole threads as you're removing the spark plugs from the hot cylinder heads. Believe me, you don't want this happening to you!
Symptoms Of Low Or No Cylinder Compression
Quite a few things can cause a rough idle condition. This includes low engine compression in one or more cylinders.
If you've got a hard-to-diagnose rough idle condition on your hands, there's a good chance it could be due to uneven cylinder compression.
Here are some other specific symptoms you may see with low cylinder compression:
- Engine cranks but does not start (0 compression in all cylinders).
- Blue smoke coming out of the tailpipe.
- Rough idle (engine misfires).
- Bad gas mileage.
- Engine 'misses' at idle but 'miss' disappears as you accelerate.
- Check engine light is illuminated with a MAP sensor trouble code (even tho' the MAP sensor is good).
As you can see, low engine compression doesn't mean the engine is not gonna' start.
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 in any auto parts store in any neighborhood, in any city, but you'll be paying at least twice as much. Go to the above compression tester links, browse and compare, you'll see a big price difference!
TEST 1: Dry Compression Test
To test engine compression, you must remove the spark plugs. This means you need to disconnect the spark plug wires from the spark plugs.
Before you disconnect the spark plug wires from the spark plugs, it's a good idea to label them with the cylinder number they belong to.
One last recommendation: Use a spark plug wire puller to disconnect the spark plug wire from the spark plug. Why? Because pulling the spark plug wire boot by hand may cause the wire's metal terminal to come loose and stay stuck on the spark plug. The following tutorial provides you with more information: How To Use A Spark Plug Wire Puller And Where To Buy One.
IMPORTANT: Do not remove the spark plugs when the engine is hot. If the engine has been running for any length of time, allow it to cool completely before removing the spark plugs.
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!
OK, to get started this is what you'll need to do:
- 1
Disable the ignition system by disconnecting the ignition coil from its electrical connectors.
Disconnecting the ignition coil will prevent it from sparking during the test. - 2
Disable the fuel system by disconnecting the two throttle body fuel injectors.
Disabling the fuel system will prevent fuel from being injected into each cylinder when the test is performed. - 3
Disconnect all six spark plug wires from their spark plugs.
IMPORTANT: Label the spark plug wires with the cylinder number they belong to before removing them. This will help you to reconnect them in the correct firing order when you're done with the compression test. - 4
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 plugs porcelain insulator crack and then you'll have a misfire on your hands. - 5
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.
- 6
Have your helper crank the engine till the needle on the compression gauge stops climbing.
- 7
Record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper.
- 8
Release the pressure on the gauge and repeat step 7 more time.
- 9
Repeat test steps 5 through 8 on the remaining 5 cylinders.
Let's take a look at what your test results mean:
CASE 1: The engine does not start and the results of the engine compression test are 0 PSI on all 6 cylinders. This test result usually indicates you have one of the following problems:
- A timing chain problem.
- A blown head gasket.
- A blown engine.
Any compression value below 100 PSI (even if it does not 0 PSI) means internal mechanical engine trouble.
CASE 2: The engine does start but the compression values you wrote down for each cylinder are slightly different from one another. Up to a certain point this could be normal, but we need to investigate a little further.
Your next step is to go to: Interpreting Your Compression Test Results.
