How To Test Engine Compression (3.2L Isuzu Amigo, Rodeo, Trooper)

Testing engine compression is becoming a standard test when diagnosing a hard-to-find misfire (rough idle) or no-start condition, especially when your 3.2L Isuzu Amigo (Rodeo, Trooper or Honda Passport) has clocked up a lot of miles.

In this tutorial, I'll walk you through the entire process step-by-step and help you interpret your compression test results to determine if one or more cylinders have low (or no) compression.

You can find this tutorial in Spanish here: Cómo Probar La Compresión Del Motor (3.2L Isuzu Amigo, Rodeo, Trooper) (at: autotecnico-online.com).

APPLIES TO: This tutorial applies to the following vehicles:

• 3.2L Isuzu Amigo: 1999, 2000.
• 3.2L Isuzu Rodeo: 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003.
• 3.2L Isuzu Trooper: 1992, 1993, 1994, 1995, 1996, 1997.
• 3.2L Honda Passport: 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002.

Symptoms Of Low Or No Engine Compression

When your 3.2L equipped Isuzu has an engine compression problem, it usually suffer one of two problems:

1. Low or no compression in one or more of the engine's 6 cylinders.
2. No compression in all 6 cylinders.

Low (or no) compression in one or more cylinders (but not all) is probably the most common problem I've seen.

This type of engine compression problem usually occurs on vehicles with a high mileage engine or an engine with a lot of wear and tear.

The main cause of low (or no) compression in one or more cylinders is usually worn cylinder head valves or worn piston rings (in the affected cylinder or cylinders).

Here are some more specific symptoms you'll see when one or more, but not all, cylinders have low compression:

1. Misfire codes (if your Isuzu 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.
2. Engine misses at idle (rough idle).
3. Lack of power.
4. Blue smoke coming out of the tailpipe at idle and/or when accelerating (this is engine oil burning in the cylinders).

If your 3.2L equipped Isuzu has 0 PSI compression on all cylinders, it won't start. The engine will crank but not start. This usually indicates that your Isuzu has a snapped timing belt, blown head gaskets or a blown engine.

The most common symptoms when there is no compression on all six cylinders are:

1. The engine cranks very fast and this fast cranking speed is very noticeable.
2. The ignition system is not creating spark (only occurs if timing belt is broken).
3. Fuel pump is working and providing pressure.

Let's get testing to see what's happening to your 3.2L Isuzu Amigo (Rodeo, Trooper, Honda Passport).

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 some recommendations to you:

The Dry Engine Compression Test

To perform an engine compression test, you need an engine compression tester.

You don't have to buy one, as you can rent one from your local auto parts store (like AutoZone or O'Reilly Auto Parts) for a cash deposit, which you get back when you return the tester.

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

   Disable the fuel system by removing the fuel pump fuse.
   
   Disabling the fuel system prevents fuel from being injected into the cylinders when you crank the engine.

2. 2

   Disable the ignition system.
   
   NOTE: This test step applies to the 3.2L SOHC engines with a 'coil pack' ignition system (1997 and older).
   
   Disabling the ignition system prevents spark from being created and delivered to the cylinders when you crank the engine.

3. 3

   Remove all 6 spark plugs.
   
   NOTE: When removing the spark plugs, be careful not to drop them on the floor (or ground), otherwise the spark plug's ceramic insulator may crack, resulting in a misfire!
   
   IMPORTANT: Label each spark plug wire with its location before you remove the spark plugs so that you can reconnect them back to the correct spark plug once you're done with the compression test.

4. 4

   Thread the engine compression gauge into the spark plug hole for engine cylinder number 1.
   
   Only tighten the compression gauge hand-tight! Don't use any tool to tighten it.

5. 5

   Have a helper crank the engine when the test is set up and watch the needle on the compression tester gauge.

6. 6

   Once the needle on the gauge stops climbing, have him or her stop cranking the engine.

7. 7

   Record the compression test result and the cylinder to which the test result pertains.

8. 8

   Repeat steps 4 thru 7 on the next 5 cylinders.

OK, let's interpret your compression test results.

CASE 1: Low or no compression in 2 side by side cylinders (of the same bank). This indicates a problem that's usually caused by:

• A Blown head gasket.

CASE 2: No compression in ALL cylinders. This isn't good and indicates that your 3.2L Isuzu has serious engine mechanical problems.

The most common issues would be:

• Broken timing belt.
• Engine threw a rod.

CASE 3: Low or no compression in one or two cylinders (that are NOT side by side on the same bank). With the compression values you have recorded, you now need to do a simple math calculation to find out if the low compression test result is within normal specs or not.

Go to: Interpreting Your Compression Test Results.

Interpreting Your Compression Test Results

It is not uncommon to see different compression values across the engine's six cylinders, especially on high mileage engines.

Up to a point, a difference in compression readings will not cause engine performance problems.

However, if the deviation between the highest and lowest values is more than 15%, your Isuzu 3.2L V6 engine will suffer from a rough idle condition or a misfire problem.

You can calculate this 15% difference in one of two ways:

• Do the math with pen and paper.
• Use my low compression calculator.

If you want to use the low compression calculator, go here: Online Low Engine Compression Calculator.

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 I got the following compression readings:

Cylinder	Pressure
#1	165 PSI
#2	95 PSI
#3	155 PSI
#4	175 PSI
#5	160 PSI
#6	155 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: Wet Engine Compression Test.

Wet Engine Compression Test

Low (or no) engine compression in one or more (but not all) six cylinders of your Isuzu's 3.2L V6 engine is usually caused by worn cylinder head valves or worn piston rings.

The cool thing is that we can figure out the cause of the low compression reading without disassembling the motor. How? By doing a 'wet' compression test.

All the wet compression test involves is adding about two tablespoons of oil into the engine cylinder that showed a low compression reading in the 'dry' compression test and retesting its compression.

If the piston rings are worn, the engine oil that has just been added will cause the compression value to increase to the average compression value of the remaining cylinders.

If the cylinder head valves are worn (for that particular cylinder), the compression value will remain the same.

Here are the steps:

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.
   
   Remember, do not use any tool to tighten the compression tester. Hand tight is fine.

3. 3

   Have a helper crank your Isuzu's engine after you've set up the test.

4. 4

   The compression test will give you 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 interpret your test result:

CASE 1: The compression value shot up. This tells you that the piston compression rings are worn and thus the problem is in the bottom end (block) of the engine in your 3.2L Isuzu Amigo (Rodeo, Trooper or 3.2L Honda Passport).

CASE 2: The compression value stayed the same. This confirms that the problem causing the low (or no) compression reading you recorded earlier is in the cylinder head valves.

More specifically, you have burned out or broken cylinder head valves causing the low (or no) engine compression condition in that particular engine cylinder.

More Isuzu 3.2L Tutorials

You can find a complete list of tutorials in this index: Isuzu 3.2L Index Of Articles.

• How To Test The Isuzu 3.2L COP Ignition Coils.
• How To Test The Isuzu 3.2L Throttle Position Sensor.
• How To Test The Isuzu Manifold Absolute Pressure (MAP) Sensor.
• Ignition Control Module Test (1992-1995 3.2L Isuzu Rodeo and Trooper).
• How To Test The GM MAF Sensor (3.1L, 3.4L, 4.3L, 5.0L and 5.7L).
  • For GM MAF sensor equipped 3.2L engines.