HELP!!! quick!!

[SHOslamwagon]

ok im searching the forum aswell at this moment looking for my answer, and my question is:

what should compression on 3.0L be? in PSI preferably?

im going to look at and engine very soon and don't really know what i should be looking for, something in the 200 PSI region? mine registered a pitiful 60.

still need help bottom post for info

 

[shoclown]

You need at least 75 psi for the cylinder to fire. Is your gauge ok? if it is you can also do a leak-down test..it is like a compression test but backwards you bring the piston up to tdc both valves closed at with tester you insert 100 psi air in the cylinder and then look and listen if you hear air comming from the oil cap,valve cover then you have a bad ring...if you hear air comming from the intake throotle body it is a intake valve..if it comes from the exhaust pipe it is a exhaust valve..
you do need the tester and a air compressor to do the test Harbor frieght has them on sale time to time for 20-30 bucks if no air compressor you can use acheap air tank at harbor frieght for 10 bucks and fill it at the gas station.

good luck

 

[Devin]

On the chart I have the maximum compression is 250. The lowest is 101. When I used to do my compression tests I'd get ranges but normally around 130-160. What you want to look for is the compression dropping while the unit is still plugged in, and more importantly that the results are all within 75% of the highest number. Such that if you get a reading of 150 and it is the highest, you want to make sure no cylinder reads under 113 (150*.75=113).

 

[SHOslamwagon]

You need at least 75 psi for the cylinder to fire. Is your gauge ok? if it is you can also do a leak-down test..it is like a compression test but backwards you bring the piston up to tdc both valves closed at with tester you insert 100 psi air in the cylinder and then look and listen if you hear air comming from the oil cap,valve cover then you have a bad ring...if you hear air comming from the intake throotle body it is a intake valve..if it comes from the exhaust pipe it is a exhaust valve..
you do need the tester and a air compressor to do the test Harbor frieght has them on sale time to time for 20-30 bucks if no air compressor you can use acheap air tank at harbor frieght for 10 bucks and fill it at the gas station.

good luck

im surprised it ran aswell, one registered at 90 and one other at nearly 0, i did the test with the engine out of the car and turned it over by hand, i did also do a leak down and it leaks everywhere, a few even out the intake and all out the rings. :S this engine is going into my wagon, so i need a good one

and thank you Devin your information is very helpfull.

 

[SHOslamwagon]

ok, now i have another question after my compression test, is it even possible to get accurate readings if im just using a ratchet attached to the crank bolt to turn it over? the engine i checked out today got like 60 on most cylinders then i tried a leakdown test and found out most likely why, air was gushing out intake and/or exhaust manifolds on most of the cylinders, is it possible to do the leakdown with it not at TDC? in my experience when its not at TDC the cylinder fires down and everything rotates.

also could this air leaking be a simple fix? because it seemed the rings were fine, no air was coming out the dipstick hole.

is their any little trick to doing either of these tests that i mite be missing? i figured leakdown was pretty foolproof, i just found the article about it from google and it was pretys simple sounding

 

[St Louis SHO]

it does not work that way, and the valves are open when doing your leakdown test.

 

[SHOslamwagon]

it does not work that way, and the valves are open when doing your leakdown test.

oooook, my compression test does not work? so how do i know if im looking at a good motor? and how will i know if the valves are closed? shouldn't they be closed at TDC? we were only pushing 90PSI. please; some help in more words

 

[93rev2sev]

You have to have the valves closed. Once they are closed, you have to prevent the engine from turning. THEN pump up the pressure and see if it leaks down.

When cranking, spray a little oil in the cyl. before putting the guage on...then crank it with the starter...not by hand.

If you got 60PSI cranking a dry cylinder by hand...you have compression.

 

[SHOslamwagon]

hmmm, ok that makes sense, but how do i know for sure the valves are closed? on my engine i had the valve covers off so i could see when they closed, however on this other engine i don't have that easyness.

 

[shoclown]

start by turning engine over as the piston arrives atdc with valves closed it will push air out spark plug hole then using a small object (like a straw or something) do not let it fall in cylinder though)stick it in the plug hole and turn crank untill piston is at top of cyclinder and start going down..now turn it back till piston is at tdc then do leak down

 

[93rev2sev]

Or just shove a length of heater hose in to the spark plug hole and hold your thumb over the end of it. Now, crank by hand. When the pressure in the hose builds....then stops...then start sucking, you are in the downward motion of the powerstroke. At the bottom of the powerstroke, the exhaust valves start to open and the sucking will stop....keep going and you wont build any pressure...thats the beginning of the exhaust stroke...don't go this far.