muffinman

I have only done compression tests on carburated vehicles. Is there anything I need to know about doing one on my 95 4.0 fuel injected engine?

99xj2.5

should be the same just disconnect coil wire and pull the fuel pump fuse.

muffinman

Yep, the fuel pump was my main concern. Sounds easy enough , thanks for the reply.

ol"blue

X2. Pull all the plugs for the test, and block the throttle open for an accurate reading.

cherokeesteve

Also do what they call a wet and dry test, it will let you know the condition of your rings.
How you do the wet and dry is you do the dry test first and take write down all the readings for each cylinder and then after you are done with the dry test go back and one at a time just before you test the cylinder for compression get an oil can with a vacuum line attached to it and squirt about 3 or 4 pumps of the oil can into the cylinder.
w
Write down and do the same for every cylinder, compare the wet with the dry and you will see the wet will be higher than the dry, it should not be higher than 10 psi per cylinder and if you are in the 20 to 40 psi difference than you have worn rings.
Hope this helps.

Willys55

While you are at it, if you have axcess to an air compressor. With all the plugs out. Start at number one cylinder and do a leak down test.
use a compression gauge kit or make the tool your self. Bascially you put a tee on the end of the hose for the compression gauge with an air chuck after a close off valve. You bring the cylinder up to top dead center and slowly open the valve to let the compressed air fill the cylinder.(Becareful engine may spin over when air is let in) This allows you to see if your valves are seating correctly.
If you hear air out the tailpipe or throttle body then you have a Big leak, otherwise just close the air valve and time each cylinder for 3 minutes and write down the amount of pressure drop per cylinder. Also before doing the leak test you need to remove the scrader valve in the compression tester or you will not see a pressure drop.

muffinman

Great, thanks for all the info guys. Gonna test this thing next weekend.