How To Test Engine Compression (1991-2007 3.3L V6 Chrysler, Dodge, Plymouth Mini-Van)

Testing the compression of all 6 cylinders on your 3.3L Chrysler/Dodge mini-van can seem quite a challenge. Mainly because of the 3 cylinders that face the firewall.

But, once you get to those spark plugs and remove them, testing and interpreting the engine's compression isn't hard. In this tutorial I'll show you how to do it in a step-by-step way and more importantly, I'll show you how to interpret your compression test results to see if there's a problem or not.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.3L V6 Chrysler Town & Country: 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.3L V6 Chrysler Voyager: 2000, 2001, 2002, 2003.
• 3.3L V6 Dodge Caravan: 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.3L V6 Dodge Grand Caravan: 1991, 1992, 1993, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.3L V6 Plymouth Voyager: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000.
• 3.3L V6 Plymouth Grand Voyager: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000.

Symptoms Of Low Or No Engine Compression

You can pretty much categorize the symptoms into 2 basic categories: Either your Chrysler is gonna' start but run rough (better known as running with a misfire). Or your Chrysler is gonna ‘crank but not start’.

Let me go into more details about both conditions:

Engine starts but runs with a misfire:

1. Also known as an engine miss, rough idle condition. Usually caused by very low compression in one cylinder or uneven engine compression that varies more than 15% across all of them.
2. Check Engine Light on with misfire codes (if your vehicle is OBD II equipped):
   • 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.
3. Bad gas mileage. This is caused by the simple fact that the engine is now running on less than all 6 cylinders, which requires those cylinders to work harder to move the vehicle.
4. Engine pollutes more.This is also caused by the simple fact that the engine is now running on less than its full complement of cylinders. The live cylinders have to compensate for the ‘dead’ ones.

If your 3.3L V-6 Chrysler equipped mini-van is NOT OBD II equipped, you won't have any codes lighting up the check engine light, but you'll definitely feel a rough idle condition.

Your Chrysler won't start:

This usually is caused by having all of the 6 cylinders with no compression. When this happens, you'll see:

1. The engine cranks very fast. This fast cranking speed is very noticeable.
2. The Ignition System is sparking all 6 spark plugs. This tells you that the no-start condition is not caused by a fault in the ignition system.
3. 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).
4. Fuel pump is working and providing pressure.
5. The most common causes of no compression on 2 or all 4 cylinders are: Blown head gasket. Or a broken timing chain. Or the engine threw a rod.

OK, having covered the most common scenarios of low compression and no compression, let's get testing to see if this is the case on your 3.3L V-6 Chrysler equipped mini-van.

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: The ‘Dry’ Engine Compression Test

In case you don't have an engine compression tester handy, you can run down to your local auto parts store and rent one.

To be a bit more specific, if you have an AutoZone or an O'Reilly auto parts store, they'll loan you one for a small deposit. Once you return the compression tester, they'll return you the deposit you put down for the tool.

If you need help deciding where to buy one or which one to buy, take a look at my recommendations: Which Compression Tester Should I Buy?

IMPORTANT: You'll be working around a cranking engine, so you have to be careful and stay alert at all times. Think safety all of the time!

This is what you'll need to do:

1. 1

   Disconnect the coil pack from its harness connector. This will prevent the ignition coil pack from firing off spark to the spark plug wires.
   
   NOTE: Disconnecting the ignition coil pack's electrical harness connector is important, since it'll prevent damage to the coil pack!

2. 2

   Disconnect the spark plug wires from their spark plugs.
   
   I recommend that you label them before disconnecting them so that you'll know what spark plug they belong to (when it's time to reconnect them).

3. 3

   Remove all 6 spark plugs.
   
   As you're taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plug's ceramic insulator to break, and this will cause a misfire!

4. 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).
   
   Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

5. 5

   When everything is set up, have your helper to crank the engine. Your job is to keep your eye on the compression tester's gauge.

6. 6

   Once the needle on the gauge stops climbing, have your helper stop cranking the engine.

7. 7

   Write down the compression value on a piece of paper. Include the number of the cylinder this reading belongs to.

8. 8

   Now repeat step 4 on the other 5 cylinders.

Let's take a look at what your test results mean:

CASE 1: No compression in 2 or more cylinders. This test result tells you that the engine has serious internal problems.

The most common issues would be: Broken timing chain. Or a blown head gasket. Or the engine threw a rod. To test for a blown head gasket, see this tutorial: How To Test For A Blown Head Gasket (3.3L V6 Chrysler, Dodge, Plymouth Mini-Van).

CASE 2: Low compression in one or more cylinders. 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.

So, your next step is to do the math and find out if these compression values are within normal parameter or not. Go to: Interpreting Your Compression Test Results.