'91 4.0 125K, air filter soaked in oil! I've pulled the CCV tube in the back of the valve cover and it has good vacuum and there isn't seem to be any blockage. The front air return/breather tube is also free. It seems that there is some oil splashing out around both grommets but more around the front one (breather). I've read the article about the blow-by that is on the shortwheelbase.com tech section but I'm still puzzled as I don't seem to find where the blockage might be. I'll try to do a test with a piece of paper to see exactly where the oil is entering the air cleaner. Any ideas? By the way on my engine the CCV metering hole is at the end of the tube and can be pulled out of the grommet. This is different from what the article describes as a grommet with a small hole in it that is part of the valve cover. ??? I need some help with this. Thanks!

oil in the air filter box is usually caused by a worn out motor. also known as blowby. if your pcv is sucking (has vacuum) then your piston rings are probably worn out.

Originally posted by JP4WHLR95
oil in the air filter box is usually caused by a worn out motor. also known as blowby. if your pcv is sucking (has vacuum) then your piston rings are probably worn out.

And if so what can I do?

Originally posted by kutyafal


And if so what can I do?

Sell the jeep:flipoff2:

Fixed mine by replacing stock CCV line with 5/16" steel line. it is a bit larger and fits the stock holes.
if that doesn't work, you are probably clogged up in your valve cover. take it off and clean out the baffles.

My 4.0 has 338km on it and this totally cured my blow by problem.
If none of the above work .....Sell it..
Good luck

It's common, check your compression with a tester if it's not less than 120psi, just toss a can of stop-smoke in the crank cas and forget about it. All Jeep straight sixes eventually puke oil into the air filter.