yj crankcase pressure

daytonaman · May 31, 2012, 12:16:28 AM

Hello, I was hoping to get some outside opinions before I start this project. I have a 1990 yj, with the 2.5L amc engine. It seems to have an excessive amount of air flowing through the crankcase. The best way I could describe it is that it acts like the exhaust is flowing through there. Now, I am under the assumption that one or more of my compression rings are bad. Could someone float some ideas this way? Am I overlooking a much simpler problem? It doesn't burn oil, and sounds good when it runs. Also, I did a compression test and the numbers were 100psi, 160psi, 130psi, and 100psi, from front to back. Any input is appreciated!

xjs3667 · May 31, 2012, 12:30:04 AM

100psi is low, you want between 120-150 on those 2.5's Im not exactly sure on the 2.5's but I know the 4.0's always have what seems to be excessive crankcase pressure. also it could be the valve guides starting to go out, as it could be burning a little oil thru them but not enough to notice but can get leak the pressure through them. also check the timing chain as they are prone to stretching and most people adjust timing instead of replacing the chain. I might be way off but I'm sure someone else will chime in if I am

daytonaman · May 31, 2012, 12:40:02 AM

Thank You, Good to know. Was planing to do rings and bearings. It'll be a good opportunity to take a peak at the head while its off. I also wondered if something isn't just gummed up or stuck. Picked the jeep up with 88k miles, and the afore mentioned symptoms are what im dealing with.

xjs3667 · May 31, 2012, 12:55:12 AM

pretty low miles, but from what I heard them timing chains usually have to get replaced around 100-120k could be less depending on hard the engine was raped

but definitely take a look at the head and valves/seats while its off

daytonaman · June 01, 2012, 01:02:56 AM

Thanks for the input, I'll look into that during the rebuild. Definately excited to have the little guy on the road soon!

daytonaman · June 25, 2012, 02:51:58 PM

A little update on the list of symptoms. Put a stethoscope to the engine and it sounds good. However, cylinder 3 is not developing any power. Tested that by removing plug wires while the engine was running to listen for rpm drop. 3 didn't cause any sort of drop in the engine rpm's

Eroq · June 27, 2012, 01:49:14 AM

plugged up cat? had them cause some funky symptoms....... pressure builds up and pushes the EGR valve open.. sometimes they squeal or make weird noises

daytonaman · July 02, 2012, 12:04:24 PM

I'll look into that, thanks

betterbeaters · July 02, 2012, 12:58:21 PM

evac system will stop crank case pressure? not sure if that will help?

daytonaman · July 18, 2012, 03:14:58 PM

Well, I'll be taking the head off, as soon as the weather cooperates. I'll learn more from there. On a side note, has any one dealt with a Jeep running really hot? anything aside from the thermostat and water pump I should look into?

xjs3667 · July 18, 2012, 05:17:30 PM

flush the rad, see how it looks in there too, could be corroded. not sure on the 2.5 again, but the 4.0 like to run hot.

what is really hot? what temp is she running at?

daytonaman · July 22, 2012, 04:33:51 PM

just a hair below overheating.

xjs3667 · July 22, 2012, 07:51:20 PM

t stat, water pump, radiator and cap, possible headgasket or head damage, make sure system is holding pressure, or it will get hot!!

daytonaman · July 26, 2012, 02:19:51 PM

Update... #3 piston ate its rings, and the head gasket was leaking into the water jacket

daytonaman · September 04, 2012, 01:45:38 PM

Update: finished overhauling the engine, and fired it up lay night.purrs like a kitten now. However, are there any tricks to getting all the air out of the cooling system? Or do i need to just wait it out?

xjs3667 · September 04, 2012, 01:53:49 PM

Fill the rad, and fire it up with cap off....... and keep adding coolant..... when it does reach temp the t-stat will open and you will know.... the coolant in the rad will go down dramatically..... fill up the rad again and when it starts to overflow out of rad put the cap on and fill overflow tank.... check the tank after driving for a while you might have to fill er up again....

BUDGETBOGGER03 · September 05, 2012, 06:27:27 PM

Quote from: xjs3667 on September 04, 2012, 01:53:49 PM
Fill the rad, and fire it up with cap off....... and keep adding coolant..... when it does reach temp the t-stat will open and you will know.... the coolant in the rad will go down dramatically..... fill up the rad again and when it starts to overflow out of rad put the cap on and fill overflow tank.... check the tank after driving for a while you might have to fill er up again....