How To Test Engine Compression (1992-2006 3.0L V6 Toyota Camry)

Performing an engine compression test on the 3.0L V6 Toyota Camry is not a task for the faint of heart.

This is because the upper intake manifold plenum must be removed to access cylinders 1, 3, and 5, which are located underneath it.

While the compression test is a bit challenging, it's definitely doable. In this tutorial, I'll explain how to do it and how to interpret the results.

With your test results, you'll know if low compression in one or more cylinders is behind a misfire or a misfire diagnostic trouble code. You'll also learn how to determine if an engine compression issue is causing a no-start condition.

APPLIES TO: This tutorial applies to the following vehicles:

• 3.0L Toyota Camry: 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006.
• 3.0L Toyota Avalon: 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004.
• 3.0L Toyota Sienna: 1998, 1999, 2000, 2001, 2002, 2003.
• 3.0L Toyota Solara: 1999, 2000, 2001, 2002, 2003.

Engine No-Start Diagnostics:

• How To Troubleshoot An Engine No-Start Problem (1992-1993 3.0L V6 Toyota Camry).
• How To Troubleshoot An Engine No-Start Problem (1994-2001 3.0L V6 Toyota Camry).

Important Tips And Suggestions

TIP 1: You'll be working around a cranking engine so make safety a priority! Use common sense and stay alert at all times.

TIP 2: The cylinder head on your 3.0L Toyota Camry is made of aluminum, so never remove the spark plugs when the engine is hot (hot = normal operating temperature). Doing so can damage the spark plug hole threads in the aluminum cylinder head.

TIP 3: If you find oil in the spark plug tubes or notice that the spark plug boots are soaked with oil, it's a sign that the valve cover gaskets need to be replaced. This oil leakage may already be causing a misfire in that cylinder.

TIP 4: To test cylinders 1, 3, and 5, you'll need to remove the upper intake manifold plenum. If you've never done this before, I recommend consulting a repair manual for detailed step-by-step instructions.

Before you begin, I also suggest taking a look at this section: Precautions To Take When Removing The Intake Manifold Plenum.

Symptoms Of Low Or No Cylinder Compression

Engine compression issues usually cause one of two problems:

1. A misfiring cylinder, causing a rough idle when the engine is running.
2. An engine that cranks but won't start.

Let's break these down:

1. Rough idle (misfire) due to low compression
   • Low compression in one or two cylinders can lead to a rough idle or noticeable shaking in your 3.0L Toyota Camry. This problem often becomes less noticeable when you accelerate.
   • If your Camry is equipped with OBD II, the PCM may record one or more of the following misfire codes:
     • 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.
   • NOTE: Keep in mind that the PCM doesn't always detect and log a misfire code, even when one or more cylinders have low compression.
2. Engine cranks but does not start
   • If three or more cylinders have zero compression, your engine might crank but won't start. When all six cylinders lack compression, you'll notice the following:
     • Faster cranking speed: The engine turns over much faster than normal, signaling a serious issue.
     • Spark is present: Each cylinder is receiving spark, which rules out problems with the ignition system.
     • Fuel is being delivered: The injectors are supplying fuel to the cylinders.
       • To verify this, you can use a Noid light to check for an injector pulse.
       • Alternatively, you can remove the spark plugs and check if they're soaked in fuel.
   • Zero compression across all six cylinders is usually caused by one of these issues:
     • A blown head gasket.
     • A broken timing belt.
     • The engine has thrown a rod.

With this overview of the types of compression issues, let's get started with 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 some recommendations to you:

TEST 1: Dry Compression Test

The spark plugs for cylinders 1, 3, and 5 are located under the intake manifold plenum. To access and remove them, you'll need to remove the plenum.

Before you begin removing the intake manifold plenum, take a look at the important precautions in this section: Precautions To Take When Removing The Intake Manifold Plenum.

While removing the spark plug wires and spark plugs, keep an eye out for signs of oil leaks. It's not uncommon to find spark plug tubes filled with engine oil or spark plug wire boots soaked in oil due to a leaking valve cover gasket.

If you notice this, it's likely causing the cylinder misfire issue you're troubleshooting. Replacing the valve cover gasket will be necessary to fully resolve the issue.

CAUTION: Be careful and be alert at all times since you'll be working around a cranking engine.

NOTE: If your Toyota's engine is hot, wait for it to cool down before removing the spark plugs. Removing the spark plugs from a hot engine can damage the spark plug threads in the cylinder head.

Alright, these are the test steps:

1. 1

   Disable the ignition system (1992-1993 with ignition distributors) by disconnecting the ignition coil from its electrical connector.
   
   This will prevent the ignition coil from sparking during the test.

2. 2

   Remove the intake manifold plenum.

3. 3

   Disconnect the fuel injectors from their electrical connectors.
   
   This will prevent the fuel injectors from injecting fuel during the test.

4. 4

   Remove the spark plugs.
   
   When removing the spark plugs, be careful not to drop any of them on the floor, or you run the risk of having the spark plugs porcelain insulator crack and then you'll have a misfire on your hands.

5. 5

   Thread the engine compression gauge into the spark plug hole for the number 1 engine cylinder. Hand tighten the compression gauge only! Do not use any type of tool to get it tight.

6. 6

   Have your helper crank the engine till the needle on the compression gauge stops climbing.

7. 7

   Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper. Release the pressure on the gauge and repeat this step one more time.

8. 8

   Repeat this test step on the remaining 5 cylinders.

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

CASE 1: You got 0 PSI compression on all 6 cylinders. This is not good and tells you that one of the following conditions exists:

• Timing belt problem.
• Blown head gasket.
• Blown engine.

Any compression value below 100 PSI (even if it does not 0 PSI) means internal mechanical engine trouble.

CASE 2: Some, but not all, of the cylinders had a low compression value. Up to a certain point this is normal -especially if the engine has a lot of miles.

What is NOT normal is if the values vary too much. With a bit of math we can find out if the lowest compression values are normal or not. Go to: Interpreting Your Compression Test Results.

The rule of thumb is that the lowest compression value cannot vary more than 15% from the highest value you recorded. Any cylinder with a compression value lower than 15% of the highest will misfire.

Interpreting Your Compression Test Results

As your Toyota's engine accumulates wear and tear, the compression of each cylinder will differ because they may wear out at different rates.

This means the compression values you obtained from all six cylinders in TEST 1 could vary slightly or significantly.

If the difference between these values is small, it won't affect engine performance. However, if the difference is too large, it can cause a rough idle or a misfire condition.

To determine whether the lower compression value is a problem, check if it's more than 15% lower than the highest compression value recorded.

You can calculate this 15% threshold in one of two ways: either manually with pen and paper or by using my low compression calculator. You can access 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 I got the following compression readings:

Cylinder	Pressure
#1	165 PSI
#2	95 PSI
#3	155 PSI
#4	175 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 Compression Test.

TEST 2: Wet Compression Test

If, during TEST 1, you discovered one or more cylinders with a compression value that's more than 15% lower than the highest recorded value, the next step is to determine whether this is caused by significant wear or damage to the cylinder head valves or piston rings.

You can do this by performing a 'wet' compression test. This test involves adding a small amount of oil to the affected cylinder and retesting its compression.

If the low (or O PSI) compression issue is due to worn piston rings, the compression value will increase with the oil added.

However, if the cylinder compression problem lies with the cylinder head valves, the compression value will remain unchanged.

These are the test steps:

1. 1

   Add a tablespoon (or two) of engine oil in the cylinder you need to retest.
   
   I suggest using a small and long funnel so that the oil will reach the inside of the cylinder.

2. 2

   Once you've added the oil, install the compression gauge, and as before just hand tighten it.

3. 3

   Have your helper crank the engine till the needle stops climbing on the compression gauge.

4. 4

   You'll see one of two results:
   
   A.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
   
   B.) The needle will not move at all or stay at the same number you recorded earlier.
   
   What ever value your compression tester reads, write it down again.

5. 5

   If you have another cylinder that needs to be tested, then repeat steps 1 thru' 4 on it now.

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

CASE 1: The compression value went up after adding motor oil and retesting. This means the low compression issue is caused by worn piston rings.

Here's why: The motor oil you added helped the piston rings form a tighter seal. With this improved seal, the compression inside the cylinder increased, which is reflected in the higher reading on your compression tester. This result only occurs when the problem is due to worn piston rings.

CASE 2: The compression value DID NOT go up after adding oil and retesting (in other words, it stayed the same). This indicates that the low compression in this cylinder, as shown in the dry test, is caused by worn or damaged cylinder head valves.

Precautions To Take When Removing The Intake Manifold Plenum

The thing that complicates doing a compression test on your Toyota's V6 engine, is the fact that the upper intake manifold plenum must be removed.

Here a couple of important suggestions that will help you avoid head-ache inducing complications:

• Begin with a cold engine: Ensure the engine is completely cool before starting to work, as hot engine components can cause burns.
• Place bolts, nuts, and parts away from the engine compartment: Keep removed bolts, nuts, and other parts in a secure location, away from the engine. This prevents them from falling into open intake ports during the procedure.
• Protect intake ports when not testing: Before beginning the compression test, cover open intake ports temporarily with a clean shop towel to prevent debris or contaminants from entering, but remove it before cranking the engine.
• Do not cover intake runners during compression testing: Do not place a shop towel on the open intake runners while performing the compression test. The towel will get sucked into the cylinder when the engine cranks.
• Use new gaskets when re-installing the plenum: Always use new intake manifold plenum and throttle body gaskets to ensure a proper seal and prevent vacuum leaks.
• Install the plenum gaskets dry: Do not apply RTV silicone or any sealant to the intake manifold plenum or throttle body gaskets during installation. These gaskets are designed to seal properly when installed dry.
• Torque bolts to specification: Torque the intake manifold plenum and throttle body bolts and nuts to the appropriate specification during reassembly.
• Ensure safe compression testing: When performing the compression test:
  • Disable the ignition system to prevent it from firing spark.
  • Disable the fuel system to prevent fuel from entering the cylinders.
  • Ensure all removed components are secured and clear of the open intake runners during testing.

More 3.0L Toyota Camry Tutorials

You can find a complete list of 3.0L Toyota Camry tutorials in this index:

• 3.0L Toyota Camry Index of Articles.

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

• How To Test For A Blown Head Gasket (1992-2006 3.0L V6 Toyota Camry).
• How To Test The TPS (1997-2001 3.0L V6 Toyota Camry).
• How To Test The MAF Sensor (1997-2001 3.0L V6 Toyota Camry).
• How To Test The Alternator (1997-2001 3.0L V6 Toyota Camry).