One of the most over-looked tests, when troubleshooting a hard to solve misfire or a no-start problem, is the engine compression test.
Over the years, I've seen lots of folks throw their hands up in the air in frustration, because not matter what got replaced (on the car or pick up), nothing solved the misfire condition or misfire code (P0300, P0301, P0302, P303, P0304).
In this tutorial, we'll explore the compression test as one of the key tests to troubleshoot a misfire code or codes (and of course a no-start problem).
This tutorial supplements the information in the tutorial: How To Diagnose Misfire Codes (GM 2.2L). Also, the info presented here applies to the GM 2.2L 4 cylinder equipped Chevrolet Cavalier, or Pontiac Sunfire, or Chevrolet Sonoma, or GMC Sonoma.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (GM 2.0L, 2.2L, 2.5L) (at: autotecnico-online.com).
Tools You'll Need:
- Compression Gauge Tester
- A Helper
- Pen and Paper
Symptoms Of An Engine Compression Problem
Engine compression issues usually fall into one of two categories:
- A low compression is in some but not all cylinders.
- 0 (zero) PSI compression in some or all cylinders.
Regardless of whether the engine has a low compression or zero PSI compression issue, you'll see a range of symptoms that will affect performance, reliability, and drivability. Some of the most common symptoms you'll see include:
Of course! Let's delve a bit deeper into engine compression issues and their symptoms.Low Compression in Some Cylinders: When one or more cylinders have lower than normal compression, it means that the air-fuel mixture isn't being compressed as effectively as it should be. This can happen due to various reasons such as worn piston rings, damaged valves, or a leaking head gasket. The symptoms of low compression may include:
- Hard Starting or No Start: The engine may struggle to start, especially when cold, or it may not start at all.
- Poor Engine Performance: The engine may feel sluggish, lacking power and responsiveness, particularly during acceleration.
- Misfiring: Misfires, where the fuel mixture fails to ignite at the right time, can occur, leading to rough idling or hesitation during acceleration.
- Excessive Oil Consumption: Oil may leak into the combustion chamber due to worn piston rings or valve seals, causing increased oil consumption and possibly blue smoke from the exhaust.
Zero PSI Compression in Some or All Cylinders: This is a severe issue where one or more cylinders fail to build any compression at all. This can be caused by catastrophic failures such as a blown head gasket, a cracked cylinder head, or a broken piston. The symptoms of zero compression are similar to those of low compression but often more severe:
- Hard Starting or No Start: The engine may completely fail to start due to the lack of compression in one or more cylinders.
- Poor Engine Performance: The engine's performance will be severely compromised, with noticeable loss of power and drivability.
- Audible Engine Noise: You may hear abnormal noises such as knocking or rattling, indicating serious internal damage.
- Reduced Power and Performance: Due to the lack of compression, the engine may struggle to produce power, leading to poor acceleration and overall performance.
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: Engine Compression Test
Each cylinder, besides needing air, fuel, and spark, to contribute to engine power, also needs to be in good mechanical condition.
If either the cylinder head valves or the engine piston rings are worn and letting the compression created on the power stroke escape, then that cylinder will misfire.
The cool thing is that the engine compression test will let us know the internal health of the engine and find out if a compression problem is causing the engine to misfire or not start.
If you don't have an engine compression tester, check out my recommendations here: Which Compression Tester Should I Buy?
NOTE: The engine should NOT be at normal operating temperature and yet, it should be not be completely cold. So, if you have just turned off the engine, after an extended run time, let it cool down completely. If the engine is cold, start’er up and let’er run about 10 minutes.
OK, here's the test:
- 1
Disconnect all 4 fuel injectors from their electrical connectors. This will prevent fuel injectors from injecting fuel into the engine cylinders.
- 2
Disable the ignition system by disconnecting all of the connectors that plug to the ignition control module/ignition coil assembly.
This important, since the ignition system must NOT SPARK. If the ignition system sparks during the compression test, the ignition coils or ignition control module can be damaged. - 3
Disconnect the spark plug wires from the four spark plugs.
NOTE: Before you disconnect them, be sure and label them so you won't lose their firing order. - 4
Remove all of the four spark plugs from your 2.2L Cavalier (or Sunfire, or S10 Pick Up, Sonoma, or 2.0L, 2.5L equipped vehicle).
Be careful and don't drop any of the spark plugs. Dropping them could cause their ceramic insulator to break and this will cause a misfire. - 5
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).
Hand tighten the compression gauge only! Do not use any type of tool to get it tight. - 6
When everything is ready, have your helper crank the engine. It usually takes about 10 seconds of engine cranking to get the maximum compression reading.
- 7
Once the compression gauge's needle stops climbing, have your helper stop cranking the engine.
- 8
Record the reading on a piece of paper along with the cylinder it belongs to.
- 9
Repeat steps 5 thru' 8 on the remaining engine cylinders.
Let's examine your test results:
CASE 1: All cylinders had 0 PSI. This test result tells you that the engine has an internal mechanical problem.
The most common causes of this condition is a broken timing chain or a blown head gasket.
Your next step should be to check the condition of the timing chain. I would also recommend that you check for a blown head gasket.
CASE 2: One or more cylinders had a low compression value compared to the others. This could be normal or it could be causing a problem.
To find out if the compression values are normal or not, go to: How To Interpret The Engine Compression Test Results.
CASE 3: All compression values were similar and above 120 PSI. This lets you know that a compression problem is not behind the no-start or misfire problem you're trying to troubleshoot.
