Leakdown Test result help pls...

Please bear with me, i done alot of reading and searching but i'm a little confused here, so help me out please :worship:.

I recently got hold of a 99 XJ with 147k on it and was thinking of doing some major build ($$$) but would like to make sure the overall condition of the Jeep before throwing in the $$$ thus these tests.

Here are the result of my compression test,

BotakBeng said:

Went over to O'reilly and rented another kit.....getting same (close) numbers.

Here is an update on warm engine (99'),
..... Dry ...Wet
#1.. 72...90
#2.. 78...90
#3.. 75...89
#4.. 81...92
#5.. 81...90
#6.. 90...86

Numbers looks better but still not in the 100's but numbers looks fairly even through out.
Thx.

Click to expand...

Here is a video of the leakdown test, with cylinder #1 at TDC (compression stroke, i double confirm with the marking on the harmonic balancer and the timing cover marking).
The only leak i detect is coming from the crankcase (no bubbles in radiatior, no hissing sound from exhaust, no hissing sound from intake manifold).

Here are some questions which i really appreciate if i can get some help,

1) With the low compression numbers i have, why is the leak % within the "low" range?

2) In the video, the % of leak went up when turn the crankshalf in an attempt to simulate when cylinder is NOT tdc but as i stop, the leak when down as if the engine was trying to seal up the leak.


I hope you are understanding me.

I tested my leakdown test kit with an air blower attachment to make sure is working and i was getting around 60% stable leak, therefore i conclude that there is nothing wrong with the kit.

Would really appreciate if someone can advise.
Thank you very much. :worship::

I don't understand what you're saying. With a leakdown tester you have to put the tester on each cylinder and bring the crank to TDC for that cylinder, and then pressurize the cylinder with a consistent input pressure. So for example you might use 100 psi of input pressure then get cylinder pressure numbers like 93, 96, 99, etc., telling you which cylinders are losing pressure. Then you run around and listen in the throttle body and exhaust and elsewhere trying to find the air noise (the leak)

Thx ehall.
This is what i did,
1) Position Cylinder #1 to TDC (compression stroke)
2) Remove spark plug and insert Adapter Hose
3) Turn regulator knob on gauge until Leak gauge reads "0"
4) Connect gauge to Adapter Hose
doing these will give me a leak % right?

Is there any power issues with the engine or are you just trying to check it out completely?
If its runs good and smooth and has good power run some seafoam thru it , a can thru the tank and do a decarb on it with the seafoam fogger.
Ive seen a decarb bring cylinders up 10+ lbs.

And dont do a decarb where the exhaust will blow on the house or a driveway ya dont want stained black.

I running fair but I'm getting low compression numbers (80ish but even through out), thus the leak down test.
What's a decarb?

BotakBeng said:

I running fair but I'm getting low compression numbers (80ish but even through out), thus the leak down test.
What's a decarb?

Click to expand...

Decrab = remove carbon deposits

The rings may be sticking, from carbon deposits. Seafoam helps remove the carbon.

Here is a link that hopefully will help the understanding of this tool:
http://en.wikipedia.org/wiki/Leak-down_tester

Compression leaks come in many forms:
Bad ring seal
Bad valve seal
Bad head gasket

The leak down tester helps examine your cylinder without removing the head.
As noted in the article, a high percentage is not necessarily "bad" but may be indicative of the engines age (general wear).

You will hear the air leak where the air is escaping.
For example: Poor Ring seal would be heard by opening the oil filler port, a burnt intake valve would hiss from the throttle body, etc.

I guess now that you have some numbers, I would look at other factors. How does the engine run? Is it consuming oil? Are the plugs a light brown, or black when you pulled them.

All things being equal, an engine with 147K is not new, and I would not expect it to have 100% compression across the board. If it is running well, doesn't consume oil, and the plugs are clean, pocket the money you were planing on soaking into the engine and drive it.

-Ron

Ecomike said:

Decrab = remove carbon deposits

The rings may be sticking, from carbon deposits. Seafoam helps remove the carbon.

Click to expand...

10 4!

WB9YZU said:

Here is a link that hopefully will help the understanding of this tool:
http://en.wikipedia.org/wiki/Leak-down_tester

Compression leaks come in many forms:
Bad ring seal
Bad valve seal
Bad head gasket

The leak down tester helps examine your cylinder without removing the head.
As noted in the article, a high percentage is not necessarily "bad" but may be indicative of the engines age (general wear).

You will hear the air leak where the air is escaping.
For example: Poor Ring seal would be heard by opening the oil filler port, a burnt intake valve would hiss from the throttle body, etc.

I guess now that you have some numbers, I would look at other factors. How does the engine run? Is it consuming oil? Are the plugs a light brown, or black when you pulled them.

All things being equal, an engine with 147K is not new, and I would not expect it to have 100% compression across the board. If it is running well, doesn't consume oil, and the plugs are clean, pocket the money you were planing on soaking into the engine and drive it.

-Ron

Click to expand...

Thx for the link!
No major issue here....just trying learn.