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lotsa blowby

M

markg

NAXJA Forum User
Location
nj
91 chero w 4.0 i got quite a bit of blowby going into the airfilter from the elbow that goes in the top of the valvecover.i do regular oilchanges and the engine is kept up quite well.there is absolutely no smoke from the tailpipe at startup or driving.any sugesstions?
 
Did you check to see if the PCV orifice in is plugged? Thats the smaller one running from the intake to the valve cover.
 
i tried to buy a pcv valve for it but the parts store said it doent use one.are u talking about just the elbows on top of the cover
 
Its actually a CCV valve and you can buy the whole kit for like 80.00 at Napa. Just tell them what you need and they have a listing for it.
 
Also, get a good seal on the valve cover. If it is sucking in any additional air, then it upsets the air flow and suck air into the air filter. Thus you get oil in your air filter.
Tom
 
Just a quick question about the ccv tube. The tube a gromet is metered for a specific size opening. Why wouldn't a larger opening tube work....better? Not talking 1/2 inch tubing but a little bigger. I am just un clear of the physics of the system I guess.
 
When I did mine, I used a later model tube. Check the MADXJ site for info. I think it is a bigger diameter. Mine was an '88 MJ, so I had to splice in rubber tubing to get the length correct. That and sealing the valve cover worked. I think I went from a quart of oil for about 200 miles to nothing.
I don't know if the metered port was bigger or the tube ID and the ID of the fitting to intake manifold.
Tom
 
Basically the CCV is a controlled vacuum leak that is hooked directly to manifold vacuum. If you increase the size of the port, you increase the amount of air flow, and therefore increase the "vacuum leak." This can cause a lean condition and also higher operating temps. But IMHO, I seriously don't think a slightly larger hose will make a bit of difference.

The purpose of the CCV is to keep negative air pressure in the crankcase to promote good ring seal, this vacuum forces air to be sucked through the fresh air vent on the front of the valve cover.

When the CCV gets plugged, then through the forces of ring blowby the crankcase gets slightly pressurized and that pressure will escape through the fresh air vent. Most of the time, that movement of air will carry oil with it and over the course of time it will build up and begin to show up in the airbox and intake tract.

Hopes this helps

Edit: Forgot that when the air exchange in the crankcase changes, and the fresh air vent is no longer "sucking" per se. Then the movement through the intake track passed the fresh air vent creates kind of a venturi effect thus drawing more air through the fresh air vent and increasing the amount of oil.
 
Last edited:
darincraft said:
Edit: Forgot that when the air exchange in the crankcase changes, and the fresh air vent is no longer "sucking" per se. Then the movement through the intake track passed the fresh air vent creates kind of a venturi effect thus drawing more air through the fresh air vent and increasing the amount of oil.
Click to expand...
Wide Open Throttle doesn't help either.
2.6mm orifice could be opened up a little, or make a catch can with a drain, a couple baffles, and some filtering media (I used copper scrubbers)
 
lonecountryboy said:
Its actually a CCV valve and you can buy the whole kit for like 80.00 at Napa.
Click to expand...
Yup, I've found NAPA to be stealership pricey too sometimes. They're generally my second-to-last result, the stealer is dead last. Try here. $17.95
 
wow ! excellent find

thanks

i pulleed all of my hoses and all were clear.the elbow in the rear of the vc was pretty clogged at the small hole in the bott of thge elbow inside the vc.i cleaned it out and ill see now how it goes.there is a rubber washer under the elbows that go into the vc.the front one is hard as a rock and the fitting is loose.oil is coming out here too.is this a dealer only item?
thanks for all of the info!
 
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