How would I go about doing a compression test on my TJ?

[DropTopDon]

How would I go about doing a compression test on my TJ? I have an 04 Rocky Mount Edition with 230k miles on the original engine. I want to see how my engine's components are holding and if they are wearing well or in good condition. To my knowledge a compression test would be a good way of checking this and gauging the health of my engine. If I were to go to the local auto store and purchase a tester, what would be my next step and what numbers would I want to look for?

 

[Chris]

It's not so much about the numbers, it's about consistent numbers and having them relatively the same (or close) between each cylinder.

As for how, here is a good video on how to do a compression test. It's easy:

 

[qslim]

The factory service manual calls for a pressure range of 120-150 psi with a variance of no more than 30psi. From the manual:

DIAGNOSIS AND TESTING—CYLINDER
COMPRESSION PRESSURE
The results of a cylinder compression pressure test
can be utilized to diagnose several engine malfunctions.
Ensure the battery is completely charged and the
engine starter motor is in good operating condition.
Otherwise, the indicated compression pressures may
not be valid for diagnosis purposes.
(1) Clean the spark plug recesses with compressed
air.
(2) Remove the spark plugs (Refer to 8 - ELEC-
TRICAL/IGNITION CONTROL/SPARK PLUG -
REMOVAL).
(3) Secure the throttle in the wide-open position.
(4) Disconnect the ignition coil.
(5) Insert a compression pressure gauge and rotate
the engine with the engine starter motor for three
revolutions.
(6) Record the compression pressure on the third
revolution. Continue the test for the remaining cylinders.
(Refer to 9 - ENGINE - SPECIFICATIONS) for the
correct engine compression pressures

You can grab your factory manual here for free.

https://wranglertjforum.com/threads...ice-manuals-fsm-technical-documentation.4618/