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blow by?

D

DDCxj

NAXJA Forum User
Location
Natick, MA
I have a 91 4.0. About a year ago I was was getting a good amount of oil in my air filter. I replaced my pcv and ccv system, gromets on the valve cover and new elbows/valves, everything. It slowed down but never stopped and the past 6-8 months its just been getting worse. The breather tube that goes from the air box to the valve cover has a lot of oil in it. What else would be causing this? should I replace everything again?

My father replaced the lifters a few months ago and when he did that he ran a compression test and that was good. I know 4.0s are notorious for blowby but this seems excessive, any suggestions?

thanks
Dean
 
I have only had my '91 XJ for about a month, so I don't know what is normal blowby for that kind of mileage. But, while I was doing all of that checking around, I found the fitting at the manifold, that connects to the rear tube at the valve cover, was carboned up and closed off. removed it and ran a stiff wire through it to open it up. It now at least sucks air through the breather tube instead blowing it toward the air filter. JMHO
 
The passages inside the valve cover can get plugged as well as the plastic lines. Doing one without the other can sometimes be a waste of time.
 
thanks for the suggestions. Old Man, what do you mean by the passages in the valve cover? where the elbows go in or is it something I have to pull the cover off for? By the way, I dont know if it makes a difference or not but I have the aluminum valve cover.

thanks
Dean
 
A few suggestions: look at the MADXJ site:http://www.madxj.com/
Check out the article on updating the system to the newer bigger CCV tube. Also, make sure your valve cover is sealed good. If your valve cover gasket lets air in, then the CCV can suck all the air in it wants to, but it can't suck enought to over come the airfilter. So the airfilter sucks oil out of the motor.
Tom
 
89xj said:
take the valve cover off and clean the inside.
Click to expand...


I'm thinking this will have to be done regularly. On my 88, I replaced both the gromets on the valve cover as well as removed/cleaned the valve cover itself. It went away for a few months but then slowly came back. Personally, I don't like spending all my free time under the hood of my jeep so I've learned to live with it.
 
Perhaps the most asked question. After all is said and done, all the PCV system replaced or cleaned, and the valve cover cover cleaned, you will still have some. Easiest way around it is to make a puke tube into a container.
BSD
 
well, I removed the lines to see if they were clogged today and none of them were clogged. I really dont feel like taking the valve cover off to clean it cause I've already done that twice. Next step I think is gonna be to do the upgrade on madxj's site and if that doesnt work I'll just live with it.

thanks for the help
Dean
 
I gave up on fixing mine and now just collect the oil. :laugh3:
Jeep on!
--Pete
24085195.jpg
 
inside the valve cover are small "chambers" with covers that resemble reed-valves... remove these covers and you will be amazed how much carbon you will find under there.. just cleaning the tube wont make this go away for very long...
 
I also replaced the original valve cover on my '88, with a '95 valve cover. I forget which article said the 91-95 VC's were better than the 87-90. Supposedly the 90 degree elbows help control the blow-by better. I did this and the MADXJ coversion. No blow-by over the next couple of months, then my Clutch Master and slave cylinder went out.
Tom
 
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