Testing engine compression is not hard and in this tutorial I'll explain the test and how to interpret its results.
With your test results you'll be able to find out if an engine compression problem is causing a rough idle/misfire problem or a 'cranks but does not start' problem.
This tutorial covers the engine compression test on the Chrysler, Dodge, and Plymouth mini-vans equipped with the 2.4L 4 cylinder engine.
Contents of this tutorial:
You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (1996-2007 2.4L Chrysler, Dodge, Plymouth Mini-Van) (at: autotecnico-online.com).
APPLIES TO: This tutorial applies to the following mini-vans equipped with the 2.4L engine:
- 2.4L Chrysler Voyager: 2000, 2001, 2002, 2003.
- 2.4L Dodge Grand Caravan: 1996, 1997.
- 2.4L Dodge Caravan: 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
- 2.4L Plymouth Grand Voyager: 1996, 1997.
- 2.4L Plymouth Voyager: 1996, 1997, 1998, 1999, 2000.
Tools You'll Need:
- Compression gauge tester
- Engine oil
- A helper
- Pen and paper
Important Tips And Suggestions
TIP 1: Don't remove the spark plugs with a hot engine.
If your mini-van's engine has been running for any length of time, let it cool down completely before attempting to remove the spark plugs.
Why? Because you run the risk of damaging the spark plug hole threads (in the cylinder head) if the spark plugs are removed with a hot engine.
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
I've noticed, over the years I've spent working as an automotive technician, that engine compression problems usually cause one of two issues.
Either the engine will suffer a rough idle/misfire condition or the engine is going to 'crank but not start' due to an engine compression problem.
To be a bit more specific, when one engine cylinder is affected with low or no engine compression, you'll feel a miss (misfire). This rough idle problem will usually cause the fuel injection computer to 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.
Besides a misfire trouble code, you'll also see one or more of the following symptoms:
- Bad gas mileage.
- Rough idle that is only felt when the vehicle comes to a stop, but that disappears when the vehicle is accelerated.
- Blue smoke coming out of the exhaust pipe when the engine is running or is accelerated.
- Engine knocks when under load or when it's accelerated.
When a compression problem causes NO compression on 2 or more cylinders the engine is not going to start.
Now, hopefully you don't have any of the above conditions affecting the engine in your mini-van but there's only one way to find, so let's get testing.
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.
Engine Compression Gauge Testers
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
The get the most accurate test result, from your compression test, it's important to test all 4 cylinders.
If you don't have a compression tester, you can run down to your local auto parts store (AutoZone, O'Reilly Auto Parts, etc.) and borrow one from them.
If you'd like to buy one and save a few bucks on its purchase, check out my recommendations here: Which Compression Tester Should I Buy?
These are the test steps:
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 to 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.