1999 XJ. Why would someone put air breathers in the valve covers like this? Previous owner did this, not sure why. I've read that there's some kind of positive negative air pressure here and there's supposed to be lines hooked up here. What kind of problems, if any, could breathers cause here? It seems some oil pools around the rear breather on top of the valve cover. The oil on dipstick smells strongly of gas fumes too, could it be related?

 

People do that to stop crank case oil vapor from getting sucked into the combustion chambers.

A better way to do that is plumb an oil/air separator catch can into the positive crank case ventilation line.

 

Why someone would do that: they're lazy and don't know any better.

Those are your PCV/CCV (positive crankcase vent/constant crankcase vent). The front is a wide open hole into the valve cover that allows fresh clean air into the block. This is typically connected to the air intake tube behind the air cleaner, but that small filter does the job just the same. The rear is more important. That one has a pinhole vent that is connected to the intake manifold. This one pulls vacuum on the block to extract fumes and burn them off. It is not working properly with that filter on there. That needs to be connected to the intake. You should remove the rear breather to clean the orifice, or replace it.

That could very well have an effect on a gas smell in your oil.

 

Back before PCV valves engines had road draft ventilation, literally a sheet metal tube that went from the valve cover and stuck down below the engine. Oil vapor any blow by combustion gasses and unburned hydrocarbons would be sucked out by the air moving under the car across the end of the tube which created a vacuum.

PCV valves effectivly do the same thing but the intake manifold is the vacuum source.

The down sides are higher milage engines have more blow by new ones and it takes more energy to burn that oil mist than is liberated by burning it. And burning it certainly doesn't help engines or catalytic converters live any longer.

I get it, brand new engines don't need catch cans so why would the factories add parts to a vehicle that won't start needing them for a hundred+ thousand miles ?

 

I have a stroker so the comparison might not be accurate....both my valves have been disconnected from the intake vaccuum on all my jeeps. The front is just a tube that always has positive pressure and blows a fine mist into my catch bottle and fills it up with a mostly watery sludge every couple of hundred miles. Point is in my jeep i have a positive crank case pressure so the " filter" would clog from the inside and be useless

 

Thinking why that was done, I am thinking the most likely possibility is some kind of problem caused the PO to delete the relevant & legal systems

That problem may be excessive blowby

How many miles does the engine have?

look at exhaust smoke to see if its burning oil

There is also anti-emissions fuel evaporator/purge solenoid etc etc, is all that present and working ?

Fiddling with anti-pollution gear will often set an OBD code, so scan it

 

Thank you, I'm going to replace the rear valve and hook it up to the intake and see how it goes. Makes sense why this would cause the oil to smell.

 

220k, no smoke at all at exhaust. It's difficult to tell if it's using oil because of a main seal leak. The oil level does lower some over time.

No codes. I'm not certain if it has all the evap stuff, like leak detection pump or vent/filter. I've seen them in videos and mine does not have them, not sure if my year, 1999, should have them or not? Here's a picture. Also I noticed in addition to the pcv nipple being plugged on top of the intake. The left most nipple is plugged too (circled). I'm not sure what that one is for. I'd love to get this jeep back to correct working order.

One more thing I've noticed which maybe it's related to the evap or pcv, when driving slowly 10 mph or less I get wafts of gas vapors into the driver window if it's down. It seems like it's coming from the engine area and not the tail pipe. No fuel leak that I've seen.

 

That year XJ should have a fuel evaporative system, it is part of an anti emission package, and I am surprised no OBD code is present, maybe that is why the deleted it

The best way is to free download the Factory Service and Parts Manual, you will be able to see what parts are missing

You would probably need to raid a wreck

 

Thanks, I found the manual. Mine was not equipped with the Leak Detection Pump (LDP) or LDP filter as indicated on the emissions sticker on the firewall. Also, the forward most nipple on the intake is not used (for mine). Federal vs CA emissions I guess. Good to know.