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91 HO Valve cover Elbows

boostamante

boostamante

NAXJA Forum User
Location
los angeles california
I'm trying to figure out if O'rielly sold me the wrong elbow for the back of the valve cover.

Originally the one in the back had a small orifice and the one i bought was hollow like the one up front ( closest to the radiator). So did they sell me the wrong one?

Also, how would it affect the engine if i installed the hollow elbow where the orifice elbow was intended to be?

The engine spews oil from those those 2 elbows and the oil cap and... the dipstick.

this sucks!
 
boostamante said:
I'm trying to figure out if O'rielly sold me the wrong elbow for the back of the valve cover.

Originally the one in the back had a small orifice and the one i bought was hollow like the one up front ( closest to the radiator). So did they sell me the wrong one?

Also, how would it affect the engine if i installed the hollow elbow where the orifice elbow was intended to be?

The engine spews oil from those those 2 elbows and the oil cap and... the dipstick.

this sucks!
Click to expand...

What part number did they give you? On the Renix XJ's, Dorman sells a new grommet and tube kit, and the orificie is actually in the tube end rather than the grommet. Install this on my 89 MJ and it works fine.

Post some pics or part numbers of what you have.
 
i dont have part numbers handy but the orifice is in the tube on the original and the one i got has no orifice
 
on the later xj's, the front one is supposed to have a large straight-through opening-that's the fresh air inlet to the crankcase.
the rear is supposed to have the same looking elbow, but the base has a little .020 or something metering orifice.
i'd think it'd idle high and run like crap with a big opening at both ends.
 
Hellbent said:
on the later xj's, the front one is supposed to have a large straight-through opening-that's the fresh air inlet to the crankcase.
the rear is supposed to have the same looking elbow, but the base has a little .020 or something metering orifice.
i'd think it'd idle high and run like crap with a big opening at both ends.
Click to expand...


I did notice an odd stumble at idle. hmm...
 
Those elbows can be compared to PCV valves, they don't " allow fresh air to the crankcase". They are positive crankcase ventilation going into the intake. So when a little bit of pressure is put in the crankcase by, well, usually a little blow by (exhaust blowing by the piston rings pressurizing the pan) then you would want that pressure out. If it is so bad as shooting more then just oil fumes out of the elbows/PCV unfortunately you got a lot of blow by gas, bad rings.
 
Think of those fancy little air filters you've seen ontop of valve cover of the sweet old muscle cars, EPA doesn't like that pressure venting thru a little filter they rather back in the intake and a BOOM will clean it up.
 
..... You could do the filter thing and plug the intake port.... If excess oil in the intake is causing the stumbling. And the rest of the engine can do it up.
 
Uhh... yes, adrnalinlovr, the front inlet DOES let fresh air in... that's why it's open and hooked to the air box from the factory. The rear hose is hooked to the intake manifold and pulls a small vacuum through the 2mm or so orifice on the whole system in order to take care of crank case pressure and fumes... the front inlet allows fresh, filtered air in to replace what the vacuum on the rear hose has sucked out.

Plugging the front inlet grommet on the valve cover is a horrible idea and will cause negative crank case pressure if the rear is still hooked up. The idea of the CCV system is to BALANCE the pressure and match it with the outside air pressure. If you have problems with oil fumes in the engine bay or oil soaking your air filter, make sure that the rear orifice is not clogged... 9 times out of 10 an oil soaked air filter is not "blow-by", it's simply a clogged rear orifice in the valve cover not allowing manifold vacuum to pull the fumes/positive pressure out.

After reading this forum for a few years, I now understand while almost every XJ or MJ has had a hacked up CCV system and problems with "blow-by" because everybody and their brother thinks they understand how the CCV system works and figures they can do it better than the factory. It works fine as it is from the factory, it is NECESSARY to have the rear grommet hooked to manifold vacuum and the front be a filtered fresh air source.

As far as the OP goes, I would take the suggestion to return the parts from the parts store and go to the dealership. At least you will know for sure you are getting the correct parts.
 
Last edited:
NotMatt said:
Uhh... yes, adrnalinlovr, the front inlet DOES let fresh air in... that's why it's open and hooked to the air box from the factory. The rear hose is hooked to the intake manifold and pulls a small vacuum through the 2mm or so orifice on the whole system in order to take care of crank case pressure and fumes... the front inlet allows fresh, filtered air in to replace what the vacuum on the rear hose has sucked out.

Plugging the front inlet grommet on the valve cover is a horrible idea and will cause negative crank case pressure if the rear is still hooked up. The idea of the CCV system is to BALANCE the pressure and match it with the outside air pressure. If you have problems with oil fumes in the engine bay or oil soaking your air filter, make sure that the rear orifice is not clogged... 9 times out of 10 an oil soaked air filter is not "blow-by", it's simply a clogged rear orifice in the valve cover not allowing manifold vacuum to pull the fumes/positive pressure out.

After reading this forum for a few years, I now understand while almost every XJ or MJ has had a hacked up CCV system and problems with "blow-by" because everybody and their brother thinks they understand how the CCV system works and figures they can do it better than the factory. It works fine as it is from the factory, it is NECESSARY to have the rear grommet hooked to manifold vacuum and the front be a filtered fresh air source.

As far as the OP goes, I would take the suggestion to return the parts from the parts store and go to the dealership. At least you will know for sure you are getting the correct parts.
Click to expand...

Thanks Nomatt, explains a lot and makes sense. Dealer probably wont have it in stock.
 
NotMatt, that was a great explanation.

As of a year or two ago, the local Jeep dealer did still stock the early HO ccv elbows....they weren't too expensive either.
 
The FSM gives two and confusing descriptions about this for a '93 XJ. On one page, it
says that the rear elbow has a metered orifice. On another page, it says that the
metered orifice is on the tip of the air tube. Maybe this was a changeover year?

I had just cleaned that tube the other day and I distinctly remembered that there was
no orifice of any kind there. I was amazed at how much black "cholesterol" washed out
of that tube.

Today, for my own peace of mind, I pulled the rear elbow off of the valve cover and
- whoila! The metered orifice is there. It measures 3/32" in diameter (I used the
butt end of a drill bit to measure this).
 
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