Dry Compression Test
If your Suzuki starts and runs, then you need to do the compression test with the engine warmed up. This will ensure a more accurate result from your compression test.
IMPORTANT: The engine should not be hot (normal operating temperature). Why? Well, because you do need to remove the spark plugs (to do the compression test) and removing the spark plugs from a hot engine can strip the threads from the spark plug hole in the aluminum cylinder head.
If the engine doesn't start, you can still do a compression test that will yield results you can use.
OK, this is what you need to do:
Disable the Fuel System. You can easily do this by simply:
- Disconnecting the fuel injector(s) from its (their) electrical connector(s).
- Or, disconnecting the fuel pump relay.
Disabling the fuel system will prevent the PCM from injecting fuel into the cylinders as you perform the compression test.
Disable the ignition system. You can easily do this by simply:
- On COP Coil systems: When you remove the COP coils, make sure they're disconnected from their electrical connectors.
- On Distributor type systems: Disconnect the ignition coil from it's electrical connector.
This step is important since it will prevent damage to the ignition coil(s), so don't skip it.
Remove all 4 spark plugs. As you're taking them out, be careful and don't drop any of them on the floor, or you could cause the spark plug's ceramic insulator to break, and this will cause a misfire!
Install the compression tester. 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.
When ready, crank the engine as you observe the needle on the compression tester's gauge. Once the needle on the gauge stops climbing, have your helper stop cranking the engine.
Write down the compression value. Record this compression reading on a piece of paper. Include the number of the cylinder this reading belongs to. Now repeat steps 1 thru' 6 on the other cylinders.
Interpret the results. After testing all cylinders and having written down all of your compression test readings, now you need to interpret the results.
Interpreting The Results Of The Engine Compression Test
CASE 1: If you got a reading of 100 PSI or less on all of the cylinders you tested. This indicates that it's time for an engine overhaul since either the piston rings and/or valves are too worn.
If your engine has reached this point, it's also burning quite a bit of oil (blue smoke coming out of the tail-pipe at idle and especially when you accelerate) and if the engine stays running, it does with a very rough idle.
CASE 2: If you got a reading of 0 PSI on all of the cylinders you tested, this usually indicates that the timing belt busted or serious internal mechanical damage.
I suggest removing the top cover of the timing belt and having a look to see if the T-Belt is busted.
CASE 3: One or two cylinders gave a low compression value. This might be normal, since each cylinder will not give the exact same pressure value.
What is NOT normal is if the pressures vary by 15% or more. How do you figure this out? You can find out by using my online compression calculator here: Online Low Engine Compression Calculator or manually this way:
- Grab a calculator and multiply the highest compression reading that you recorded by 0.15.
Let's use the following compression readings to explain the point:
- Cylinder #1 175 PSI.
- Cylinder #2 160 PSI.
- Cylinder #3 165 PSI.
- Cylinder #4 95 PSI.
- The next step is to do the math: 175 x 0.15= 26, 175-26= 149.
- So then, 149 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.
- This means that cylinder #4 is the one causing the misfire
The next step is to do a ‘Wet’ compression test on the dead or low compression cylinder and this test is explained in the next page.