Doing a compression test on your 2.0L (SOHC/DOHC) or 2.4L (SOHC/DOHC) has now become an easy thing! This tutorial will show you how to do the engine compression test and more importantly, how to interpret the results of the compression readings you're gonna' get from the compression tester.
This article is geared towards solving a misfire condition (with or without codes: P0300, P0301, P0302, P0303, P0304) or a rough idle condition, although if your vehicle does not start, this info still applies.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (Chrysler 2.0L, 2.4L) (at: autotecnico-online.com).
Tools You'll Need:
- Compression gauge tester
- Engine oil
- A helper
- Pen and paper
Important Tips And Suggestions
TIP 1: If your 2.0L or 2.4L Chrysler vehicle cranks and starts then it's best to do the compression test with a slightly warmed up engine.
This is because as the engine warms up, all of it's metal moving parts (like piston rings, valves) expand with the heat the engine is creating. This will have an effect (however small) on your compression tester reading.
If the engine doesn't start then don't worry about this, since you'll still be able to get a compression test result you can use.
TIP 2: You'll need a helper to crank the engine for you, while you eye-ball the compression tester.
My suggestion to your helper wait outside the vehicle till you're done setting up the test. Once the test is done, ask you helper to wait outside again. This will help you to avoid having him or her accidentally crank the engine while you're setting up the test.
Symptoms Of Low Or No Engine Compression
When only one engine cylinder is affected with low or no engine compression, you'll feel a miss (misfire) and you can usually bet that the PCM will set a misfire trouble code:
- P0300: Random Cylinder Misfire.
- P0301: Cylinder #1 Misfire.
- P0302: Cylinder #2 Misfire.
- P0303: Cylinder #3 Misfire.
- P0304: Cylinder #4 Misfire.
Unfortunately the PCM won't always set a misfire code to tell you which cylinder is the one that's missing.
The next common scenario is having Low or No engine compression on two engine cylinders. When this happens, the engine in your car will crank but not start. This usually indicates a blown head gasket.
If a blown head gasket is a concern then take a look at this tutorial I've written: How To Test For A Blown Head Gasket (Chrysler 2.0L, 2.4L).
When you have a situation where you have NO compression on ALL 4 cylinders, you'll see:
- When you crank the engine over, it cranks very fast and this fast cranking speed is very noticeable.
- You'll have spark (in every cylinder), so you know it's not an ignition system issue.
- The fuel injectors spray fuel.
- You can confirm this with a Noid light test.
- Also, you can confirm this, although indirectly, by removing the spark plugs and checking to see if they are fuel soaked (fuel fouled).
- The most common causes of this scenario, are:
- Blown head gasket.
- Broken timing belt (which is the most common scenario).
- Engine thru' a rod.
Now, hopefully you don't have any of the above conditions affecting the engine in your car but there's only one way to find, so let's get testing.
TEST 1: Dry Engine Compression Test
Before you jump into the tests, read this entire tutorial first. Be sure you're familiar with the test steps and above all, take all necessary safety precautions, since you'll be working around a cranking engine. Take your time, be alert and use common sense.
This test article assumes that the engine starts and runs and that you're testing a misfire condition. But if engine cranks but does not start, don't worry -you can still use the info in this tutorial.
OK, let's get this show on the road:
Disconnect all 4 fuel injectors from their electrical connectors.
This may not be possible on all models (since some of the fuel injectors may be inaccessible due the the intake manifold plenum covering them). The next best thing is to remove the Auto Shut Down (ASD) Relay. This will also prevent fuel injectors from injecting fuel into the engine cylinders. This step is important!
Disable the ignition system.
It's important that, while you're doing the test, no spark is fired from the spark plug wires. You can easily accomplish this by disconnecting the ignition coil pack.
Remove all of the spark plugs.
Take care not to drop any of them, since dropping them can damage them and cause a misfire condition later.
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.
Have your helper crank up the engine.
Now the engine will not start (of course), but the idea is to crank the engine long enough to have the compression tester gauge's needle stop climbing. This usually takes about 10 seconds of cranking.
When the needle stops moving (as the engine is being cranked), have your helper stop cranking the engine.
Write down this compression reading, along with the cylinder's number, on a piece of paper.
Repeat steps 5 thru' 7 on the rest of the cylinders.
Now, let's take a look at what your test results mean:
CASE 1: Your compression tester recorded NO compression on all cylinders. This isn't good and tells you that you have one of the following problems:
- Broken timing belt.
- Blown head gasket.
- Engine thru' a rod and is now junk.
CASE 2: Your compression tester recorded low or no compression on one or two cylinders. The next step is to interpret those numbers (compression numbers) you obtained from the tests. Go to: Interpreting The Results Of The Engine Compression Test.