Compression test results
 

My Jeep has never seemed to have the power that my friends 4.0L jeeps do. Did a compression test today for the hell of it, this is what i found.

Im not sure what it "should" be, so my question I guess would be How does it look?

http://farm8.staticflickr.com/7025/6...b0522b15_z.jpg

Wow, my renix at 250000+ km was 140psi on all six...

This one has only 220,000 kilometers (136,000 miles)

Leak down test?

The only thing significant about those numbers is cyl #5......it's headed south. The range/variance of the numbers hi/low should be less than 10%.

Did you do this test with the engine hot or cold because that will affect the numbers.

Correct way to do a compression test is with the motor warm, all spark plugs removed and throttle held wide open while starter motor is cranked.

engine was cold.

And - make sure each cylinder gets an equal number of pulses.

Watch while it pulses - at least 90% of the final value should happen with the first pulse.
95-96% on the second pulse.
Max pulses should be 4.

Some people crank and crank till they get what they want - totally invalid!

How do they "get what they want"?:confused:

I like 7. Just seems thorough. X2, warm, leak-down, 10%. What year? Is yours really doggen or are they just louder? If you are sure everything is right and it's doggen, once I had a clogged cat do that. Finally I loosened the bolts on the header pipe on (her "K" car), and WOW, night and day, that was it.

I'm still puzzled about 140 psi on all six......seems physically impossible.:sweatdrop: Leak down and compression test are 2 different animals.

??? "Leakdown" is the term I've always used for "wet", a few tablespoons of oil in there. Admittedly that doesn't sound right.

Well...just googled it, I stand corrected. Done with compressed air.....

#5 is a bit off but overall there's nothing wrong with these numbers for a 4.0 XJ

What should the ideal or target compression numbers be for a 97 4.0?

Flash

The strength of your battery, and starter, as well as their cables and connections, and even the viscosity of your oil will all affect your range of readings. Also the ring end gaps are smaller warm. The test can revile a fault such as a cracked valve, bad head gasket or a bad cylinder. If the reading rises significantly after adding a small amount of oil to the cylinder, it can be presumed that the (compression loss), was largely past the piston. It's the difference between the readings that gives the most important information.

I wheeling recently, decided to check the oil the other day and the dip stick was pushed out. I am assuming this would be cause by crankcase pressure build up, but what would be the most likely cause to look at?

The front tube from the valve cover to the air cleaner should be free to flow.

Maybe there?

Normal numbers for a 4.0 should be 120 to 150 no less then 30 psi per cylinder