Perfect timing as I replaced mine just yesterday. I bought my '96 4.0 ZJ two years ago. Soon after buying it I was checking the crankcase ventilation system and found mine wasn't working. The 4.0 doesn't have a PCV "valve" per se. The plastic elbow at the rear of the valve cover is metered and functions similar to a PCV valve. In other words, it has a small hole in the bottom which regulates the amount of vacuum pulled by the intake, not a spring loaded plunger as a PCV valve would. The front elbow, connected by a tube to the air cleaner assembly, allows clean air to enter the crankcase. The front elbow is wide open at the bottom. To test to see if your system is working, remove the hose going to the air filter and put your finger over the end of the hose. You should feel a small amount of suction. That's what the metered elbow and the rear of the valve cover is allowing through. If you have no suction (like mine did two years ago), the rear elbow is plugged. HERE'S WHERE THE PROBLEMS START!
Those old rubber grommets can get real hard, so much that you cannot remove the plastic elbows. When I checked mine two years ago I was able to force a screwdriver under the flange on each side of the CCV (rear) elbow and gently pry it out of the grommet, after squirting some oil around it. I then used brake cleaner and a small drill bit to clean out the orifice. THAT WAS TWO YEARS AGO. I tried to pry out the CCV elbow a couple of weeks ago and it wouldn't budge. In fact, I broke off part of the flange. Humph!
I was already planning on replacing my valve cover gasket, so I decided to do it all in one shot. I bought the valve cover gasket (Felpro P/N VS50458R, $45), then went to the Jeep dealer and bought the CCV elbow ("crankcase vent", P/N 53030495, $13), and two grommets (both elbows take the same grommet (P/N 2946079, $9 each).
I thought I had everything wired. GUESS AGAIN. Removing the valve cover off sounds easy, but is more difficult than it should be. Just follow a shop manual (like Haynes). A couple of tips. The rear elbow might cause enough interference with the cowl that you'll have to break it off just to lift the valve cover high enough to get it over the rocker arms and out. Also, that rear bolt is a bear to reach. I ended up using a 7/16" deep socket, a 2" extension, and a small ratchet (all 3/8" drive).
After I got the valve cover off and cleaned up, I tried to remove the front elbow (which I had planned on reusing) and what was left of the rear elbow. No way, Jose! Those rubber grommets had fossilized and wouldn't let loose of the elbows, even after using oil. I ended up breaking the front elbow too! Another run to the Jeep dealer to get P/N 53030991, $5.
Back to working on the valve cover. I ended up breaking off all of the flange on both elbows just to gain access to all of the gromets. Then used a utility knive to cut the grommets up into small pieces and finally hacked away at them enough to get them and the remains of the elbows out. I would not want to try all of this with the valve cover on the engine. You wouldn't want to drop any pieces down into the valve cover, even though the inside of the top of the cover has a baffle that runs the full length, with only a large opening for the oil filler cap. Besides, it's easier to do this type of work on a bench rather than bending over an engine. Before you reinstall the valve cover, thoroughly clean the surface on the head being very careful not to knock any of that gunk into the head. Also, while you're there, you might as well check the torque on your rockers. Good luck. Just be prepared.
'96 ZJ, 4.0L, 42RE, NP242, stock D30 and D35-LS w/ 3.73, 4-1/2" lift, 32" BFG ATs, Magnaflow, JKS track bars and disconnects, spare tire carrier, Optima red top, ROLA roof rack, KC SlimLite driving lights, CB and Yaesu ham radios, GPS
Last edited by ZJJay; 12-06-2009 at 09:17 PM.
Reason: Making it more readable.