compression test

[LIFTEDXPLODER96]

i just did a compression test on my 4.0L as well as new spark plugs and wires. i have been looking everywhere for the compression specs on the 4.0 but can find it. here is what i got #1:151 PSI #2:151 PSI #3:151 PSI #4: 150PSI #5: 152 PSI #6: 150PSI.....i think its pretty good compression. if not please lat me know..Thanks!

 

[James909]

Those numbers look really good to me. I'm not sure of the Ford spec but unless the numbers are really low the most important thing is that there is not a big difference between the cylinders. And you can't get much closer than that.
Edit: I just wanted to add that a general rule of thumb is ideally you want to have less than a 10% difference between the highest and lowest cylinders.

 

[LIFTEDXPLODER96]

ok cool. thanks for letting me know

 

[Maniak]

on a 4.0 ohv (ours was a '92), we got 165 as the best number on a few cylinders.. (no.. ours weren't all the same.. hence the rebuild )

~Mark

Edit: I found a post I made a while ago (before the engine rebuild, but after an exploded spark plug)...

We have 310,000 miles on ours... Our motor is still doing well.. I have 160 compression all the way around EXCEPT for one cyl that has 130

I say your numbers are really good (nice and close).

 

[LIFTEDXPLODER96]

ok thats good to know. they seemed like good numbers to me. i am leaking a bit of coolant looks to me like its behind the water pump. maybe tomorow i will post a pic of the general spot of where the leak is. its just one thing after another haha but i still love my dependable 4.0l it been a great engine

 

[Cobraguy]

Those numbers would make me feel pretty good...especially if it was a dry test.

If you really want to know the condition of your engine, buy a good quality leak down tester and "leak check" the engine. That will tell you exactly what percentage is leaking and you should be able to tell where. Valuable tool to have in your box if you are going to keep and maintain older vehicles. Plus your buddies will be VERY impressed!

 

[LIFTEDXPLODER96]

thanks cobra. how much does a leak down tester cost?

 

[Cobraguy]

You can get them dirt cheap from Harbor Freight or you can spend some money for high quality ones. Google for cylinder leak tester or leak down tester.