Oily air filter

I just bought my cherokee and today I took out the air filter to take a look at it. It is black and oily. What does this mean?

It runs great, a few hesitation moments at idle, I think are the spark plugs. My buddy says use Champion $2.50 a hit, so $15 total.

Typically it means that your rear vent hose (crank case vent) that hooks in to the back of your valve cover is clogged. I had the same issue.

Oil filter dirty (oily): See those two grommets/tubes coming off the top of your valve cover? The rear one of those is likely plugged and forcing the blowback out the front one onto your oil filter. Go to NAPA
and get new front and rear vacuum sets.

You should also familiarize yourself with the search tool. The advanced option is what you need, and how you would have found an answer to your question.

kujito and mudfrog offer some great advice. I would like to add that when these Jeeps were new that they were oiling the air filters. We used a fix at the dealership, per JeepTech, and I don't remember if it was ever published in TSB form. We removed the valve cover and turned it upside down to see the tubes that protruded down toward the head. The tubes are directly below the above mentioned grommets. The fix was to remove the tubes via 3 screws and then cut 1/2" off the bottoms, clean them up and reinstall them. Kinda funny, but last week when I was working on putting an HO in place of my Renix engine in my 88 xJ, I decided to look under both valve covers. The tubes on the HO valve cover are shorter.

Your first homework is to read this article. Lots of other good information like this on this forum and the web. SEARCH for "jeep blowby".

http://jeep.off-road.com/jeep/article/articleDetail.jsp?id=257985

Back some years ago I had that problem with my 87. I cleaned out the tube, but the fittings were cracked. I went to the dealer (yeah, I know, but that's where I went) for a new rear vent hose and fittings, and found that there had been a change in the design. Where the original had sharp 90 degree fittings, the new one had gentler curves. Now that would not seem to be such a big deal, but the new hose cured the blowby almost completely, and it behaved well for a good distance past 200 K miles. So I'd suggest, if you can, that you replace the whole shebang (not necessarily at dealer prices) if it still has the sharp-cornered fittings on it.

A certain amount of blowby is pretty common with this design, and I wouldn't worry about a little black spot on the filter as long as it doesn't start really oiling up.

FYI, I had this issue, replaced the vent hoses, still had it. I pulled the grommet out for the rear vent hose. It was so old and dried that it had sealed itself shut. It was like it had melted all of the rubber inside the valve cover together. I replaced it. No more problems. I thought you might be interested in that, as mine is an 88 as well.

You might find hard and crusty oil ish on the rear vent. I forget what earlier years(pre 95) had the easy twist 90* and remove elbows, but you might have to take the valve cover off, and use a poker/small scredriver of sorts, carbon cleaner, and compressed air to clean out the elbows and tubes.

Thanks for the info
After posting this thread, I did google it and found great info on it.
I actually replaced the rear rubber valve cover grommett from the junk yard. Used a long flat head screw driver to pop it out, making sure I didnt hurt it too bad., Mine was clogged with a black hard sandy substance. The front one is a little more work, I have the front valve cover grommet but will have to cut both ends and connect them up. Mine didnt stay in the hole because it was damaged, the new junk yard one fits great, just have to find a way to connect them by cutting.

Get some thin wall metal tubing, cut a short piece then glue/clamp it on both rubber pieces.

Very common problem, the junk yard had numerous custom jobs. Will get something that fits the hose.

Thanks

Napa sells the rear grommet with plastic tube for $8.

If you have a lot of that black hard sandy gunk, consider taking the valve cover off and giving it a thorough cleaning. The crankcase vent system on the 4.0 is a strange design, apparently depending on a delicate balance of pressure and vacuum, and sometimes, I think, on the phases of the moon or the transit of mars. Inside, beneath the grommets, are baffles, and it seems that the condition and cleanliness of the baffles has some bearing on it all. When I opened up my 87 it yielded a huge amount of baked-on stuff, including a fair amount that had fallen onto the rockers and the head.