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.
Contents of this tutorial:
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 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 in any auto parts store in any neighborhood, in any city, but you'll be paying at least twice as much. Go to the above compression tester links, browse and compare, you'll see a big price difference!
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
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
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
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
Have your helper crank the engine till the needle on the compression gauge stops climbing.
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.
Repeat this test step 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.
