Some questions

[AngryLepercon]

So this is all new to me. I never worked on my own cars till now cause I just don't trust the stealerships anymore. I needed a vacation from work so I took off today and I'm going to work on the ranger. 99 4.0ohv. It has problems. I'm going to be doing a compression check but reading the forums and searching I turn up all different ways to do it. I work on 12 cylinder CAT 992's not 4.0 v6's so I'm kinda confused. I would love to learn this kind of stuff. Preventive maintenance and check up stuff.

What should be the average pressure be in each cylinder for a 4.0 with 130k miles?

I know each motor varies but I'm looking for a ballpark range. As well as numbers that tell me its completely trashed. So I can decide and price a rebuild or a 302 swap.

Also I have no idea exactly how to do said test. Again searching hasn't turned up much for the OHV just the SOHC. If anyone has a link or info on it I would really appreciate it.

Plans are right now to change plugs and wires as well as compression test. Maybe its the plugs but the test could show something different.

Thanks for any help. Rep will be added for any information

 

[Maritime Storm]

A compression test is performed by removing a spark plug, installing the gauge, pushing throttle wide open and cranking the motor long enough to produce a few compression strokes. The readings should be within 15 PSI of each other, a minimum of 100PSI and this should be done on a cold engine. If you have a low cylinder, add a small amount of oil(no more than 1/4 ounce) into that cylinder and re-test that cylinder if the readings increase substantially you may have worn rings in that cylinder, if not you may have valve sealing issues.