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Oil In AIr Filter/Not Passing CA Smog


NAXJA Forum User
So, maybe a noob question, but I'm new to this issue. I'm trying to pass smog (CA, uggg) and I'm failing in just the last category, NO at 25mph. Anyway, going through everything, and I find my air filter (K&N) is covered in oil. So now I'm reading about CCV/PCV valves. I know I replaced these in the last 10 years. But the front one (CCV?) isn't super tight where it attaches to the engine. I mean, it's on there good, but I can rattle it around a bit, I'd be shocked if it was airtight. Is it supposed to be? I don't remember it ever being "airtight" tight, but I haven't really paid much attention to it either.

Should I just replace all this stuff and clean the filter? Maybe just blow out the hoses with air and replace the elbows and grommets I guess...? Hoses look fine. Everything looks fine actually, but front elbow/grommet just not super tight.

Jeep runs amazing. Changed oil, O2 sensor, and got some CataClean to use for next test (any tips with that stuff are welcome too. Saw a recommendation somewhere online)

As always, thanks for any help-

At the risk of confusing things more....

Your K&N is supposed to be covered in oil However, it's with the K&N oil, not engine oil. Do you use the K&N oil or do you run the filter dry?

The elbow towards the front of the engine provides fresh filtered air back into the engine. If it has a lot of engine oil in it, you may be experiencing a lot of blow by.

The elbow at the rear of the VC has a metered orifice in it. This elbow connects to the intake manifold. Make sure the orifice is clean and clear, and the hose is in good shape. Vacuum draws fumes from the engine into the intake to burn. Fresh air is drawn from the front elbow. If the orifice is blocked/restricted, then fumes can push back through the front elbow.

NO is generally caused my high combustion temps. Check your cooling system. Fresh oil, spark plugs always help (check the coloring of the old ones). I'm not familiar with that brand but fuel system cleaner is also a good thing.

Make sure you drive it hard before going back for testing. Get that CAT up to temp. Make sure you don't have any exhaust leaks.
Man it's been so long since I serviced that K&N I forgot there's oil on it. But 99% sure this is engine oil. filter is almost black. Oil on AF cover from hose outlet from engine. Is that front grommet on VC to air filter supposed to be airtight? Mine is not. I do think I'm getting a lot of blow by.
Specially since they are cheap I would replace the grommets and at least the orfice elbow and check all the hoses, but it does sound like you have excessive blow-by. You might consider a catch can on the hose to the intake manifold.
Here's the one I run on my stroker......


Nice setup- wow that is clean-

looking for the grommets and elbows for my 1991... I'm seeing them on Amazon for 1994+... Anyone know if there's a difference...? I know they changed the VC on the 4.0 around then...
What type of FelPro gasket? Cork, Rubberized cork or the Silcon rubber one? I kind of feel that there is an imbalance of air. The front orifice is sucking to much air. So, a leak somewhere in that system. I don't know if it is 'legal' in CA, to put on one of those valve cover breathers on the front hole of the valve cover. Also, I think the 93-95 ZJ is a bit better valve cover than the 91-95 XJs. I did have this issue with my '88 MJ. Also, try and find Cruiser's tips, and the valve cover tower modification. I remember it being a factory FSM.
Thx 75SV1. I think it's the silicon one. I found the part #s and ordered the proper grommets/elbows for the 1991. They are different. They look to be 1-piece grommet+elbow. A lot of comments said the front one did not fit tight. I am going to assume this is not a problem. I am going to dig into it this wknd. I am fearing that the wrong elbow is on the rear of the VC. They might both be the same rt now..? I'll look into a valve cover replacement from a JY at some pt. I have read they are much better. Rt now I just need to pass stupid smog. This is my DD. I'll check out cruisers tips fo sho
Speak of the MJ.
Also, Dino might have a cheap catch can design. Also, I did use the latter XJ Big CCV tube on my setup for the '88 MJ. I got that tip from the MAD XJ site. Doubt its still up and running. Also, might see about putting on a late XJ steel valve cover. At least to pass smog. I haven't tried it on earlier 4.0Ls without the positioning post head bolts.
Good to know, tech1001. I cannot for the life of me figure out how to post photos on this site. Anyone got any info on how to?

The only thing I failed was NO at 25mph. Max allowed 613, I measured 739. At 15mph it was 711 and 677, PASS.

At 25mph: CO% was 0, HC was 18, %CO2 was 15.2, %O2 was 0.
Be real careful to save all documentation for the new cat and the installation.

Kali screwed me over on the cat in my '96 XJ. Even though it had met the legal requirements when it was installed they would not accept it anymore because they had changed the rules. Unless I could provide the original, dated, installation invoice from a legitimate shop they would not accept the existing cat. Even though it clearly passed the sniffer test.

If you have paid attention you know Kali likes to change the rules. Just one more way they express how well they know better than you what is best for you.
Have you tried the other suggestions? The CARB certified CAT is about $600. I think a $10 can of whatever system cleaner is worth a shot.

Also make sure you drive a good distance at a good speed to get the cat really hot and burn the stuff out of it.

You can test the cat using an IR thermometer. Once up to temp (like after the drive above), with the engine still running, use an IR thermometer to read the temps at the inlet and exit to the cat. The exit should be hotter than the inlet somewhere in the 30-100 deg range.

If you end up replacing the cat, as ANAK suggests, keep all of the documents, including your smog tests. I'm not aware of any law that prevents a DIY install. However, the testing shop has to "certify" that all emission components are installed and functioning correctly.

I last replaced mine in 2014 with a direct fit. Didn't have any issue with it being DIY.
Great info. I replaced the O2 sensor, Oil+Filter, Air filter, CCV and PCV hoses, Ran a bottle of Fuel injector cleaner, and a bottle of CATAclean through 2 tanks of fuel. Drove for 30mins before getting test. Still failed NO2. I'm assuming 30mins is enough to heat up the Cat? In any case, I'm thinking my Cat may be shot. My last cat was in 2013, 60k miles ago. I guess it's time to replace. The one before that only last 40k. Great info on documentation. I'll get it all. I want a guarantee from shop it's a legit unit. Stay tuned...
SOLVED: Following up here. I did replace CAT, no change. Ran all sorts of cleaners through fuel: BG44, various brands of injector and chamber cleaners no change. Best test was Nox= 707@15mph and 830@25mph/FAIL.

Finally, swapped out Dist Cap + Rotor. BAM. Easy Pass. Nox=7@15mph, 108@25mph.

Live and learn

I would not have expected that.

Pricey lesson. Thank you for sharing. Hopefully it will spare someone else the pain.