How To Test The Engine Compression (2.5L Suzuki Verona)

Testing the engine compression on your Suzuki Verona's 2.5L L6 engine is pretty easy. This is due to the fact that the spark plugs, which have to be removed for the test, are easily accessible.

Checking the compression of all 6 cylinders is probably one of the most overlooked tests, when diagnosing a rough idle or no-start condition.

In this tutorial, I'll show you how to do and interpret the results of your 'dry' and 'wet' engine compression test results.

Important Tips And Suggestions

TIP 1: If the engine starts and runs, on your 2.5L Verona, it's a good idea to warm up the engine for about 15 minutes before starting the compression test. The key words here are 'slightly warmed up engine' since the engine should not be hot.

Why warm up the engine? Because a slightly warmed up engine will improve the accuracy of your compression test results.

TIP 2: Take all necessary safety precautions as you work around a cranking engine. Your safety is your responsibility, so use common sense and think safety all of the time.

TIP 3: The cylinder head, on your Suzuki, is made of aluminum so you should never remove the spark plugs if the engine is hot (hot = normal operating temperature). Removing the spark plugs from a hot engine can/will damage the spark plug hole threads in the aluminum cylinder head.

Symptoms Of Low Or No Cylinder Compression

For the most part, engine compression problems fall into 2 basic categories: Low engine compression in one or two cylinders and no compression in all cylinders.

Low engine compression in one or more cylinders will cause a rough idle issue that can seem very hard to diagnose.

No compression in all cylinders results in a 'cranks but does not start' condition.

Here are some other specific symptoms you may see with low cylinder compression:

• Misfire diagnostic trouble codes: P0300, P0301, P0302, P0303, P0304, P0305, P0306.
• Engine cranks but does not start (0 compression in all cylinders).
• Blue smoke coming out of the tailpipe.
• Rough idle (engine misfires).
• Bad gas mileage.
• Engine 'misses' at idle but 'miss' disappears as you accelerate.
• Check engine light is illuminated with a MAP sensor trouble code (even tho' the MAP sensor is good).

With this info under our belts, let's head down to the next subheading and 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 some recommendations to you:

TEST 1: Dry Compression Test

You'll need to remove the spark plugs for the engine compression test and this will afford you the chance to see if the spark plug wire boots and spark plugs are swimming in motor oil (from leaking valve cover gaskets).

Leaking valve cover gaskets that are letting the spark plug tubes fill up with motor oil are a very common problem on the 2.5L L6 engines. This problem will eventually result in a misfire condition as the oil cooks and creates carbon tracks on the spark plug or spark plug boot.

So, if you do spot a spark plug wire boot covered/dripping in oil, you've found a the potential problem behind the misfire you're trying to diagnose with the compression test (you should still proceed with the compression test though).

OK, to get started this is what you'll need to do:

1. 1

   Disable the ignition system by disconnecting the ignition distributor from its electrical connector. This will prevent the ignition coil from sparking during the test.

2. 2

   Remove the spark plugs from a slightly warmed up engine (if it starts and runs). Remember, the engine can not be hot!
   
   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.
   
   If the engine does not start, don't worry about it being warmed up.

3. 3

   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.

4. 4

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

5. 5

   Now, record on paper the value at which the needle stopped and the number of the engine cylinder on a piece of paper.

6. 6

   Release the pressure on the gauge and check this cylinder's compression one more time.

7. 7

   Remove the compression tester and check the compression on the remaining 5 cylinders.

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

CASE 1: Your vehicle does NOT start and you got 0 PSI on all cylinders. This test result usually means that the engine has a serious internal mechanical problem.

The engine might have one of the following:

• Timing belt problem.
• Blown head gasket problem.
• Engine threw a rod.

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

CASE 2: The compression values differ from one another. This could be normal or it could be causing a problem.

To find out if the low compression values are withing a normal range or not, go to: Interpreting The Results Of The Engine Compression Test.

CASE 3: All 6 cylinders have a compression value of less than 100 PSI. This indicates an internal engine problem.

This test result is usually caused by one of the following:

• Timing belt problem.
• Worn piston rings.
• Worn cylinder head valves.

Interpreting The Results Of The Engine Compression Test

There's a good chance that the compression values you wrote down for each cylinder are slightly different from one another. This could normal and nothing to worry about yet or it could be a problem.

What could cause a problem is if the cylinder compression values vary too much. The cool thing is that we can find out if the variations in the values, you wrote down, indicate a problem (with that cylinder) or not.

The rule of thumb is that they can not vary more than 15% from each other and if they do, you're gonna' have a genuine misfire condition on your hands or possibly a no-start condition (if more than one cylinder is affected).

How do you figure this out? You can find out by using my online low compression calculator here: Online Low Engine Compression Calculator or manually this way:

• 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.

To make better sense of the above calculation, let's say that I got the following compression test results:

Cylinder	Pressure
#1	175 PSI
#2	170 PSI
#3	165 PSI
#4	120 PSI
#5	165 PSI
#6	170 PSI

The next step is to do the math:

• STEP 1: 175 x 0.15 = 26.25.
• STEP 2: 26.25 = 26.
• STEP 2: 175 - 26= 149.
• ANSWER: 149 PSI is the lowest possible compression value.

Since cylinder #4 is producing 120 PSI, I can conclude that it's the one causing the misfire. The next step is to find out what's causing the low compression value. Go to: TEST 2: Wet Compression Test.

TEST 2: Wet Compression Test

Low cylinder compression is usually due to 1 of 2 things. Either the cylinder head valves (of the affected cylinder) are severely worn/damaged or the piston rings are worn/damaged.

You and I can find out by adding a small amount of motor oil to the low compression cylinder. This is what is known as a 'Wet' compression test.

If the problem is bad piston rings, the motor oil that we're gonna' add will help bring the compression value up when we check that cylinder's compression again.

If the problem is bad cylinder head valves, the motor oil WILL NOT help raise the compression value of the cylinder. It's as simple as that!

OK, this is what you'll need to do:

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

   Now, have your helper crank the engine till the needle stops climbing on the compression gauge.

4. 4

   You'll see one of two results:
   
   1.) The needle will climb higher than the previous compression number you recorded for this specific cylinder.
   
   2.) 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, repeat steps 1 thru' 4 on it now.

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

CASE 1: The compression gauge registered a higher compression value after adding motor oil. This tells you that the low compression problem is due to worn piston compression rings.

Here's why: The reason the compression value shot up is due to the fact that the motor oil you just added helped the piston rings to create a tighter seal. This type of test result only happens when the problem is due to worn piston rings.

CASE 2: The compression gauge DID NOT register a higher compression value after adding motor oil (in other words, it stayed the same). This result tells you that the low compression value registered in this cylinder (in the dry test) is due to worn/damaged cylinder head valves.