Compression test?
Thread Starter
6th Gear Member
Joined: May 2006
Posts: 6,448
From: Ohio
Compression test?
Does anybody have a good write up on how to do a compression test or could just tell me. Also what all i will need. I know the basics but just looking for a good indepth HOW TO.
3rd Gear Member
Joined: May 2006
Posts: 831
From:
RE: Compression test?
Basically you want to start with a good compression tester. I like the ones with the base that screws into the spark plug boss and has a "quick disconnect" for the hose and gauge. You're going to need to disable the ignition so the car will not start, only crank over. After that, screw in the tester, crank the engine over a few times and read the gauge. You'll want to do it after the engine is warmed up though to allow for ring expansion and such.
If you need a "how to" just look for a write up on how to change the spark plugs.
If you need a "how to" just look for a write up on how to change the spark plugs.
2nd Gear Member
Joined: Apr 2006
Posts: 417
From:
RE: Compression test?
To kill the spark just unplug the crank trigger sensor but you'll probably have to unplug all of the cops anyway. Make sure you shut off the fuel, either by the relay or the inertia switch in the trunk, just smack the bracket with a rubber mallet and the red button should pop up. The motor should be warm, ALL plugs removed and the throttle plate wide open, good luck.
6th Gear Member
Joined: Sep 2005
Posts: 5,128
From:
RE: Compression test?
Once you disable the fuel and spark...
You will want to remove all 8 spark plugs and set them up in the order they came out so you can inspect them.
Then, one cylinder at a time, screw the compression tester into the spark plug hole. Hold the throttle at WOT and crank it over 3-5 revolutions. Do this twice per cylinder, and then record both values. You will average each pair of numbers for each cylinder. Now, mind you, every book I have read has indicated you need to do this at operating temp. I'd say let it cool off about an hour before testing, for the sake of less hand-burns.
Write down all the numbers on a piece of paper so that they correspond to the cylinder's location. What you are looking for is consistency. You want them all to be around 150 psi. +/- 10 psi. And the highest one should only be 5-10 psi higher than the lowest cylinder. If you have huge differences, then you have problems.
One more test you can run while doing this, is after doing the above described test, squirt a bit of oil into each spark plug hole and let it sit. Then repeat the same compression test. If the numbers go up, your piston rings are shot. If not, your bottom end is probably good.
You will want to remove all 8 spark plugs and set them up in the order they came out so you can inspect them.
Then, one cylinder at a time, screw the compression tester into the spark plug hole. Hold the throttle at WOT and crank it over 3-5 revolutions. Do this twice per cylinder, and then record both values. You will average each pair of numbers for each cylinder. Now, mind you, every book I have read has indicated you need to do this at operating temp. I'd say let it cool off about an hour before testing, for the sake of less hand-burns.
Write down all the numbers on a piece of paper so that they correspond to the cylinder's location. What you are looking for is consistency. You want them all to be around 150 psi. +/- 10 psi. And the highest one should only be 5-10 psi higher than the lowest cylinder. If you have huge differences, then you have problems.
One more test you can run while doing this, is after doing the above described test, squirt a bit of oil into each spark plug hole and let it sit. Then repeat the same compression test. If the numbers go up, your piston rings are shot. If not, your bottom end is probably good.
Thread Starter
6th Gear Member
Joined: May 2006
Posts: 6,448
From: Ohio
RE: Compression test?
ORIGINAL: monkeydude3
Once you disable the fuel and spark...
You will want to remove all 8 spark plugs and set them up in the order they came out so you can inspect them.
Then, one cylinder at a time, screw the compression tester into the spark plug hole. Hold the throttle at WOT and crank it over 3-5 revolutions. Do this twice per cylinder, and then record both values. You will average each pair of numbers for each cylinder. Now, mind you, every book I have read has indicated you need to do this at operating temp. I'd say let it cool off about an hour before testing, for the sake of less hand-burns.
Write down all the numbers on a piece of paper so that they correspond to the cylinder's location. What you are looking for is consistency. You want them all to be around 150 psi. +/- 10 psi. And the highest one should only be 5-10 psi higher than the lowest cylinder. If you have huge differences, then you have problems.
One more test you can run while doing this, is after doing the above described test, squirt a bit of oil into each spark plug hole and let it sit. Then repeat the same compression test. If the numbers go up, your piston rings are shot. If not, your bottom end is probably good.
Once you disable the fuel and spark...
You will want to remove all 8 spark plugs and set them up in the order they came out so you can inspect them.
Then, one cylinder at a time, screw the compression tester into the spark plug hole. Hold the throttle at WOT and crank it over 3-5 revolutions. Do this twice per cylinder, and then record both values. You will average each pair of numbers for each cylinder. Now, mind you, every book I have read has indicated you need to do this at operating temp. I'd say let it cool off about an hour before testing, for the sake of less hand-burns.
Write down all the numbers on a piece of paper so that they correspond to the cylinder's location. What you are looking for is consistency. You want them all to be around 150 psi. +/- 10 psi. And the highest one should only be 5-10 psi higher than the lowest cylinder. If you have huge differences, then you have problems.
One more test you can run while doing this, is after doing the above described test, squirt a bit of oil into each spark plug hole and let it sit. Then repeat the same compression test. If the numbers go up, your piston rings are shot. If not, your bottom end is probably good.
6th Gear Member
Joined: Sep 2005
Posts: 5,128
From:
RE: Compression test?
well you just squirt it in the spark plug hole and let it sit, with the angle of the piston it will eventually run down to the cylinder walls, and turnin the engine over will accomplish this too
it's just a way to see if you are losing compression past your rings
it's just a way to see if you are losing compression past your rings