Another blowby thead

I have the XJ blow by problem. Mostly only if I spend a long time on the freeway. Perhaps I should be looking for the real problem but I have considered all the option like the bottle trap to catch the oil and whatever. My latest idea seems like it may really solve the symptom. Is there any reason you couldn’t get a real PCV valve and put it in the big tube that goes from the Valve cover to the air cleaner in such a way that air could not move the wrong direction? ( From the VC to the Air box) I have replaced all the vac hoses and that didn’t help. I guess the next thing would be to pull the valve cover and clean it out. But wouldn’t the check valve give me a clean left fender in the interim.

The big tube is for when the throttle is open, the small tube is for when the throttle is closed (mostly). The small tube replaces the PVC valve (found in many motors). I doubt the large tube would have the vacume to open a PVC valve much, if at all (the PVC is normally in the intake manifold, not the air cleaner side of the system).
The grommet the small tube hooks up to, is probably plugged, find a suitable length of tubing, and try blowing through it backwards. Blow through the small tube, doesn´t take much to plug it up. Clean mine twice a year spring and fall.
You may have too much blowby for the system to handle, at the oil filler hole,with the cap off, rev it a couple of times, should be very little smoke, hold your hand lightly (warm motor, not hot) over the opening, if the pressure forces your hand off the opening, something is seriously pluged and/or it´s ring time.
There have been many threads, about synthetic oils in an older motor. A 10-50 synthetic, has worked well in older 4.0 motors for me, seems to help some with cronic problems, such as blowby (a little) and low oil pressure (some). Haven´t sprung any new leaks, as a matter of fact, some of the older seeps dried up (think the gaskets swelled a touch).

instead of trying to band-aid the issue.. its really an easy fix.. the large tube feeds clean filtered air into the crankcase and the small one is a vacuum that pulls the "bad" air out and into the intake system.... if the small tube clogs you will force pressure out the big tube, which should be under a vacuum from the crankcase side... if you cant clear it out with carb cleaner and a wire.. you need to pull the valve cover off.. under each tube is a small chamber with a "flapper" type metal baffle inside it.. pull off the chamber covers and you wouldnt belive how much hard carbon crap was built up inside it.. a wire brush and some carb cleaner.. or better yet a parts cleaner if you can get access to one... will clear out the build-up/ blockage.. slap it back together with a new gasket and your all set.. i had so much oil blowing into my air filter and leaking on that side of the engine that it actually softened the motormount rubber and it all squished out like a gooey sponge... you will probably need to replace the big hose too since the oil has probably swelled it inside... take a lil more time and do it right instead of putting in a pcv that wont do anything good to your system..
good luck..
mike

I agree with striptide about fixing it right. I had the problem on my 88 XJ. By reading my owner's manual I found out the big tube and little tube are to be replaced every 50,000 miles. When I got my XJ with 101,000 it still had the factory pieces and oil in the air filter.

I went down to the lacal dealer and purchased the 3 pieces of the continuous crankcase ventilation (CCV) at the dealer. Expect to spend the better part of a $100 bill. I installed them and flipped the filter to see if any more oil came out. It was a week or two and there was no more oil on the air filter.

At 115K I pulled the valve cover and cleaned it out like the article on cherokee america said, thought that would fix it. My intake was pretty clean, just a coat of carbon on the little doors at the top of the snorkels.

I then noticed at 120K I was getting oil in the filter again so I decided to change the CCV pieces again. I also shortly after that had the cat converter changed.

I changed my Cat at 125K miles. Once the Cat was changed the problem was fixed. The cat was causing back pressure which was messing with vacuum.

If you still have the stock cat and over 100K miles I'd recommend changing it as a routine maintenance. If you notice the passenger's floor getting very warm that one of the indicators.

Also if you replace the CCV harness' you may fix most of your vacuum leaks since new vacuum lines are included.

The problem with the CCV system is the little tube gets stopped up. When that happens the only place for air to come out of the engine is the big tube. There is a TSB out to change out the little tube and install a improved grommet in the valve cover. they also changed the shape of the tube so there were not low points.

Also if you have a vacuum gauge check the vacuum at the intake manual. I measure like 16-17 in Hg. My dealer mechanic tells me that good. He said if I had 12 in Hg then you need to have the top end/intake cleaned. Here an excuse to buy a new tool

I never seen the partially plugged cat listed in any of those web articles but I know it worked for me - new CAT and new CCV tubes. I have 28K on this set of tubes and plan to keep them for the full 50K instead of chaning them at a 30K interval.

Bronco said:

wouldn’t the check valve give me a clean left fender in the interim.

Click to expand...

The pressure inside the engine has to go somewhere, and if you put a check valve in the large tube, the pressure will build up in the crankcase until it finds the easiest way out, which may be past the front or rear crank seals, oil pan or valve cover gasket, and '87s didn't come with a seal in the distributor housing, so if you haven't replaced the distributor yet, it's one more place for the oil to leak out.

sidriptide said:

the large tube feeds clean filtered air into the crankcase and the small one is a vacuum that pulls the "bad" air out and into the intake system....

Click to expand...

Until you put a load on the engine, then manifold vacuum drops to zero, and blow-by goes to maximum! Then everything reverses direction and the pressure in the crankcase forces the blow-by through the large tube into the air intake so it can be burned in the engine, same result, just a different route.

The '88 XJ I recently delivered to Montana had massive oil in the air cleaner when I arrived at the end of the trip. Had a local shop replace all the CCV stuff, and the new owner has informed me by e-mail that it's still dripping oil. Problem is, she's totally non-mechanical, so she can't describe where it's coming from.

Two of the guys in the North Atlantic Chapter have converted the small tube to a conventional PCV with valve. The first to do it stole the grommet and valve out of a Chevy S-10 2.8L that was sitting dead in his yard and found they fit, so that's what he runs. But he also runs a conical air filter, so he doesn't have the same oil collection problem.

The second guy took his hint from the first, but he runs a K&N flat filter in the stock box. And he recently inspected it after several months with the PCV and found the filter soaked with engine oil. Something is not working, but what?

I checked with the dealer and found that the PCV valve for the 2.5L I-4 is not the same listing as for the 2.8L V-6. I think if you need a different valve to go from 2.5L to 2.8L, you must certainly need a different valve when you jump from 2.8L to 4.0L, and then factor in the added blow-by of an older engine.

Proposed solution: The PCV valve for a 1985 Eagle 4.2L is the same outward configuration as the ones for the 2.5L and 2.8L. I suggest trying that. Replace the intake manifold fitting for the brake booster hose with a "tee", and connect the PCV hose to that.

Mark's going to try it, and if the lady in Montana confirms that her drip is still into the airbox, I'll make up a kit with those parts and send it to Montana for a trial run.

If you try it, let me know how it works.