How To Test Engine Compression (1991-2010 3.3L V6 Chrysler, Dodge, And Plymouth Minivan)

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, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 3.3L V6 Chrysler Voyager: 2000, 2001, 2002, 2003.
• 3.3L V6 Dodge Caravan: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007.
• 3.3L V6 Dodge Grand Caravan: 1991, 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010.
• 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.

CYLINDER MISFIRE DIAGNOSTICS:

• How To Troubleshoot A Cylinder Misfire (1996-2010 3.3L V6 Chrysler, Dodge, And Plymouth Minivan).

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 these recommendations to you:

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 (1991-2010 3.3L V6 Chrysler, Dodge, Plymouth Minivan).

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.

Interpreting Your Compression Test Results

If you got a low compression reading (in TEST 1), the next step is to find out if this compression value is causing a problem.

What you have to do is find out if this low compression value varies by more than 15% of the highest compression value you obtained from your tests.

Why? Because if the low compression value varies by more than 15%, then this cylinder is going to misfire and can be considered 'dead'.

You can do this one of two ways: You can calculate this 15% difference with pen and paper or you can use my low compression calculator. You can find the low compression calculator here: Online Low Engine Compression Calculator (at: easyautodiagnostics.com).

If you want to manually calculate the 15% difference, here's what you'll need to do:

• STEP 1: Multiply the highest compression value by 0.15 (this is the decimal value of 15%).
• STEP 2: Round the result to the nearest one (for example: 25.6 would become 26).
• STEP 3: Subtract the result (the number that was rounded) from the highest compression value.
• ANSWER: The result of this subtraction is the lowest possible compression value any cylinder can have.

Now, let me give you a more specific example: Let's say that my 3.3L V6 Dodge Grand Caravan produced the following compression readings:

Cylinder	Pressure
#1	165 PSI
#2	95 PSI
#3	155 PSI
#4	175 PSI
#5	160 PSI
#6	165 PSI

My next step is to do the following calculation:

• STEP 1:  175 x 0.15 = 26.25.
• STEP 2:  26.25 = 26 (rounded to nearest one).
• STEP 3:  175 - 26 = 149.
• ANSWER:  149 PSI. Any cylinder with this compression (or lower) value will misfire.

Since cylinder #2 is only producing 95 PSI, I can now conclude that it's 'dead' and causing a misfire.

To find out if the lowest compression value you got from your engine compression test is within a good range, you'll need to do the same calculation. Of course, you'll need to use the highest compression value you got and not the one in the example.

Once you've found the 'dead' cylinder, the next step is to find out what's causing the low compression value. For this step, go to: TEST 2: 'Wet' Engine Compression Test.

TEST 2: 'Wet' Engine Compression Test

If you got a cylinder with low or no compression (either would be considered 'dead'), the next step is to do a wet compression test.

This test will help pinpoint the problem to either bad cylinder head valves or bad piston compression rings.

Now, to explain what's involved in a wet compression test, you're gonna' add about two tablespoons of oil to the confirmed 'dead' engine cylinder or cylinders.

Depending on the compression test result of the cylinder you added oil to, you'll be able to determine if the low compression reading you recorded in the dry compression test is caused by worn piston rings or worn cylinder head valves.

OK, this is what you need to do:

1. 1

   Add a small amount of engine oil to the cylinder that reported low compression or no compression in the 'Dry' compression test.
   
   The amount should be about 1 to 2 tablespoons of oil.

2. 2

   Install the compression tester onto the cylinder.
   
   Do not use any type of tool to tightened the compression tester. Hand tight is fine.

3. 3

   When all is set up, have your helper crank the engine.

4. 4

   You'll get one of two results:
   
   1.) The compression value will go up (from the one you recorded before).
   
   2.) The compression value will stay the same.

Let's take a look at what your test result means:

CASE 1: The compression value shot up. This tells you that the piston compression rings are worn out and thus the problem is in the bottom end (block) of the engine in your 3.3L Chrysler mini-van.

The reason why is that the oil you just added helped the piston rings seal better, thus causing the compression reading to rise.

CASE 2: The compression value stayed the same. This confirms that the problem is in the cylinder head valves.

The reason for this is that nothing, not even the engine oil, can help the cylinder head valves seal the compression in the cylinder. So, if after adding oil and retesting the compression the compression value doesn't increase, then you now know that the problem is in the cylinder head valves.

More 3.3L V6 Chrysler, Dodge, And Plymouth Minivan Tutorials

You can find all of the 3.3L V-6 Chrysler/Dodge/Plymouth equipped mini-van diagnostic tutorials here:

• 3.3L V6 Chrysler, Dodge, And Plymouth Minivan Index Of Articles.

Here's a sample of the tutorials you'll find in the index:

• How To Test The Alternator (2001-2004 3.3L Chrysler).
• How To Test The MAP Sensor (2001-2004 3.3L V6 Chrysler And Dodge Mini-Van).
• How To Test Engine Compression (2001-2007 3.3L Chrysler).
• How To Test The Coil Pack 3.3L, 3.8L Chrysler, Dodge, Plymouth (1990-1998) (at: easyautodiagnostics.com).
• How To Test The Coil Pack 3.3L Chrysler, Dodge, Plymouth (1999-2001) (at: easyautodiagnostics.com).
• How To Test The Coil Pack 3.3L, 3.8L Chrysler, Dodge, Plymouth (2001-2008) (at: easyautodiagnostics.com).