Topic: Cylinder Compression Pressure

[bukdwn]

I'm having trouble with finding the compression pressure for a 1995 2,5 engine. I just did a dry compression test on my jeep. I came up with
#1 Cylinder  137 psi
#2 Cylinder  134 psi
#3 Cylinder  131 psi
#4 Cylinder  145 psi
     The book tells me pressure should be 155 to 185.   I've read somewhere that 120 to 150 is right.   ANY help would be appreciated!   
     1995 2.5 yj  with 95.000 miles.  Very well taken care of,  Mostly highway miles.     No motor modifications except airbox mod 

[sharpxmen]

seems a bit low but not extremely. I would guess this was at cold otherwise would be bad from what i remember, i did one myself at some point and posted the results - i'll see if i can find the post. Do one after reaching the operating temperature (thermostat opened) and post the results.

EDIT: i found my test from a while ago http://4bangerjp.com/forums/index.php/topic,7216.0.html

i remember i did one with the engine hot as well later but i didn't post the result unfortunately, from memory were all 170 to 180 and the difference was not that much between cylinders as it was at cold but in my case def #3 is in need of at least a set of rings.

[grumpygy]

You are good as far as the difference between cylinders.     Warm will be higher.  You can also squirt some oil in the cyl to see if its valves or rings where you are losing pressure.  If after you put oil in and it goes up its rings.  Stays the same and its valves.

[bukdwn]

Thanks guy's.      Maybe you guy's can help!  Last week i was having idle problems.  I did a fuel pressure test at the rail and it was 80 psi. Looked further and found that the fuel return line was clogged. all fuel lines passed.  I dropped the tank and problem solved.  I found that the bottom of the skid pan was dented (small dent) pounded it out and installed tank and did another test.  Now it is 35 psi, all good.  So also was seeing that my temps have been going up a little, More like sporadic.   It usually runs about 195, but it was running close to 210.  I've been reading about the FoMoCo mod so i decided to go to the pick and pull about an hour away. Bought me a 2 speed 95 Ford tauras. My clutch fan was not working by the way, so this would be a good mod.   I did a pressure test on the cooling system. Pumped up the gauge to 15 lbs and was loosing about a pound a minute.  No leaks what so ever.  Do you guys think it could be the head gasket?  

[bukdwn]

Still trying to find out the compression #'s 120 to 150  or 150 to 180 .  120 to 150 sounds more like it for a 4 cylinder.

[bukdwn]

  I also want to add that i did a full tune up on the jeep. Plugs, wires, rotor/cap. I also drained the radiator fluid and replaced the thermostat. Install a USA stainless 195 degree thermostat. Put the front of the jeep on some ramps to burp the water bubbles.  Also the new fan has been mounted to the existing radiator shroud. You cant even tell there is a electric fan except for the original clutch fan missing. Right now i have it on a manual switch. I did order a Flex-A-Fan adjustable temp. control and will be hooking that in to the system. I want to keep the manual switch. I don't think it is to hard to figure out how to install the adj.temp control.   Thanks to Jeffy's write up, this has gone pretty smooth and all the input from others!

[sharpxmen]

your fuel pressure should be 39psi with the vac line disconnected, once you connect the vacuum line should drop to 31 or so (i'm assuming we're talking YJ)

cyl pressure test should be the same between 2.5 and 4.0, maybe slightly less on the 2.5 but i wouldn't think more than 5psi

warm test would give you a better idea of what's going on with the motor i think.

as far as rad pressure test, it's hard to tell, but if it's the cyl head gasket you'd have either coolant in the oil or would leak in the cylinders, so if you keep pressure in it long enough you should be able to find out (with the plugs out bring the cyl 1-2 at TDC and stick a cotton stick like the ones you clean your ears with in there, would absorb some coolant if any of it gets in there, then repeat for 3-4, if it goes in the oil you'd see a foamy deposit on the valve cover cap or the breather). Could also be as simple as leaking where you apply pressure, that you can find with a soapy water that you'd brush around there, should bubble if it leaks at that spot.

[bukdwn]

Thanks for the help. good idea on the cotton swabs!!     This morning i removed the ox sensor.  Oh, by the way Yes it is a YJ. Anyways i pulled the ox sensor and the outer metal was kind of powdery whitish color.  I ordered a new one and should be here in a couple of days.   Lately, the engine lite would come on at about 190 degrees .  The code that comes up is #21 oxygen sensor. I know i have (2) different things going on but would high fuel pressure lead to any of these problems I'm having?  Would 80 lbs of fuel pressure at the rail cause the ox sensor to wack out 

[grumpygy]

Just a quick Question have you been losing any radiator fluids.

[sharpxmen]

Thanks for the help. good idea on the cotton swabs!!     This morning i removed the ox sensor.  Oh, by the way Yes it is a YJ. Anyways i pulled the ox sensor and the outer metal was kind of powdery whitish color.  I ordered a new one and should be here in a couple of days.   Lately, the engine lite would come on at about 190 degrees .  The code that comes up is #21 oxygen sensor. I know i have (2) different things going on but would high fuel pressure lead to any of these problems I'm having?  Would 80 lbs of fuel pressure at the rail cause the ox sensor to wack out 

if you have a CEL for o2 sensor then just replace it, it's bad.

35 psi fuel pressure is still off but if that was with the vac line connected it would be just fine as you'd get about 43 with it disconnected and a lot of guys are running that pressure already, the other way (line disconnected and 35 psi) would be lean at wot

[bukdwn]

Grumpygy, I have not been loosing radiator fluid from what i can see. Also checked the overflow can and it is good. 

[bukdwn]

Sharpxmen, I did not know to remove the vacuum line from the fuel pressure regulator. Thanks for info..  I will have to re-test in the morning. Sounds like I'm OK though. I really appreciate the help..  The jeeps never let me down.  Lately though it's had some hiccups..       Would like to install a new alternator. I've read on hear that a 1997 8.0 v10 dodge 136 amp would bolt right up.    I'm not the best at electrical and the requirements to do it properly.  Bolting it up with stock wiring (no Problem) but if their must be different wiring than I'm hoping that someone could give me a drawing of the proper way to install the right fuses and wiring diagrams.    I would really appreciate it.   Thanks Again Guy's ,    James....

[grumpygy]

Reason I ask about fluid loss.  is from above.

Could also be as simple as leaking where you apply pressure, that you can find with a soapy water that you'd brush around there, should bubble if it leaks at that spot.

[sharpxmen]

like he ^ said, if you're not missing coolant it's probably nothing

for the alternator check the FAQ, there's a list of bolt-on ones that require no major mods, i have one from a GC. Only problem is you will be limited to 100Amp on stock wiring, do a search as there are a few threads on this topic (there's a recent one as well).

[bukdwn]

Thanks again for all the help and information!  James...