In this tutorial you'll find instructions on how to do and interpret a compression test on your 3.0L equipped Nissan Maxima (Pathfinder, Quest or D21 Pickup).
You'll also find the ‘Wet’ compression test explained so that if you do find a cylinder with low (or no) compression... you can find out if it's due to worn cylinder head valves or bad compression piston rings.
Contents of this tutorial at a quick glance:
- Important Tips and Suggestions.
- TEST 1: Dry Compression Test.
- TEST 2: Wet Compression Test.
- Which Compression Tester Should I Buy?
Puedes encontrar este tutorial en Español aquí: Cómo Verificar la Compresión del Motor (3.0L Nissan) (en: autotecnico-online.com).
Important Tips and Suggestions
TIP 1: If your 3.0L equipped Nissan starts and runs, it's standard procedure to do the compression test with a slightly warmed up engine. The key words here are ‘slightly warmed up engine’ since the engine should not be hot.
To slightly warm up the engine, start her up (from a completely cold condition) and let her run for no more than 10 to 12 minutes.
TIP 2: You'll be working around a cranking engine as you perform the engine compression test so take all necessary safety precautions. Your safety is your responsibility... so use common sense and think safety all of the time.
TIP 3: Never remove the spark plugs with a hot engine. This is important because the 3.0L V6 engine has aluminum cylinder heads. Removing the spark plugs from a hot engine can damage the spark plug hole threads in the aluminum cylinder heads.
TEST 1: Dry Compression Test
To test the engine's compression, you'll need to remove all six spark plugs. My recommendation is to label all spark plug wires (or ignition coils) and spark plugs with the cylinder number to which they belong to. This is done for two reasons:
- To install everything back faster and without complications.
- To diagnose a cylinder's misfire back to a specific component (like a worn out spark plug, damaged spark plug wire, etc.).
Also, it's a good idea to blow compression air around the spark plug before removing it to remove any large particles that may fall into the spark plug hole (after you've removed the spark plug).
OK, to get started this is what you'll need to do:
Disable the ignition system (if distributor equipped) by disconnecting the ignition distributor and/or the ignition coil from their electrical connectors. NOTE: Do not skip this step since disabling the ignition system will prevent ignition system damage.
Disable the fuel system by removing the fuel pump fuse. Disabling the fuel system will prevent fuel from being injected into each cylinder when the test is performed.
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.
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.
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 3 cylinders.
Let's take a look at what your test results mean:
CASE 1: If Your Car Does Not Start and the results of the engine compression test are 0 PSI on all 4 cylinders then you have one of the following conditions:
- Timing belt (or timing chain).
- 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: If Your Car Does Start, the very first thing you'll notice is that the compression values you wrote down for each cylinder are slightly different from one another. This is normal.
What is NOT normal is if the 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?... This is how you do it:
- Grab a calculator and multiply the highest compression reading that you recorded by .15. So, let's say that cylinder #4 gave you the highest reading of 170 PSI. Well 170 X .15 gives you 26 (25.5 rounded off).
- Now, the next step is to subtract 26 from 170... which gives us 144 PSI.
- So then, 144 PSI is the lowest possible compression reading that any one of the rest of the engine cylinders can have. Any compression reading below this.. and that engine cylinder will misfire.
To make better sense of the above calculation... let's say that my 3.0L Maxima produced the following compression test results:
- Cylinder #1 170 PSI.
- Cylinder #2 175 PSI.
- Cylinder #3 170 PSI.
- Cylinder #4 170 PSI.
- Cylinder #5 165 PSI .
- Cylinder #6 120 PSI .
The next step is to do the math: 175 x .15= 26, 175-26= 149. So, now I know that cylinder #6 is the one causing the misfire!!