Topic: Bad blowby

[Got Wood?]

I have a 90 yj, I just got it a couple of months ago, it had 199,000 on it when I bought it. It had terrible blow by so I replaced the pcv and replaced the missing hose that goes to the air filter box. This didn't help much so I replaced the valve cover(after cleaning the old one and then cracking the nice plastic pos).This seemed to help for a little while but now the valve cover is covered with oil again and it is also dripping out of the air filter box. When it is cold it shows about 75psi on the oil pressure gauge and then after it warms up it shows 40 at idle and 75 at 2800 rpms.I haven't tried changing the sending unit or a mechanical gauge yet but it seems like it has so much pressure it blows it out past the grommits on the vc. I am not sure what to do about it, any help would be appreciated, thank you

[wrangler387]

Try to use some engine flush or seafoam... something along those lines. Your oil pressure is definately high. You are definately get to much buildup of pressure inside the motor. I'm not talking about oil pressure, actual crank case pressure. You sure everything is hooked up correctly?

[Got Wood?]

No, I am not sure everything is hooked up right. It had several dry rotted vacuum lines and missing line from rear of valve cover to air box. I am not even sure the motor is original, says xj on intake and some of the bell housing bolts don't appear to be oem. I ran some sea foam through the fuel tank a couple of tanks ago and poured in a quart of lucas with the last oil change.Should I try some sea foam in the oil?Thanks for the reply.

[Jesse-James]

I don't know if it will help, but that's one of the first things I do with any vehicle I buy. Sea foam in the gas, oil, and trans if auto and change all fluids after a couple hundred miles. Have had nothing but good results.

[wrangler387]

Definately try and either run engine flush through the oil or seafoam. I'm not a fan of any oil additives. Just run a straight 10w30 motor oil. I think Jeffy has manuals saved to his computer that should have diagrams of all of the vacuum lines... Send him a PM, but i'm sure he'll read this thread.

[chardrc]

i got a 90 yj with 159000 miles last year and it would backfire when shifting and leak oil and what fixed it for me was a new valve cover(old one cvracked.. not your problem thoguh) and we had to pull the motor to put a new clutch slav cylender in and after we put in the motor again the back fire was gone and it ran beter.. luckly and after replacuign a few horibly bad roted oily vacum lines..

[BK2LIFE]

your rings might be bad.  you could possible need a rebuild, do a compression check and see if your gettin blow by past the rings and pressurizing the crank case

[Beachbum]

Don't know if this will help you either but I'm will to share it with you anyway. I don't know what the 90 model has for sure, I have a 91. When I bought it it was sucking oil into the airbox and satuating the air filter in less than 100 miles, on the 91 it has what is called a CCV valve instead of PCV valve it is only a brass fitting in the valve cover with a small hole in it, I pulled it out and found it was plugged with gunk. Cleaned it out, reinstalled it, connected the vacuum line and the problem was solved. Make sure everything is right before assuming the rings are gone.

[Jeffy]

your rings might be bad.  you could possible need a rebuild, do a compression check and see if your gettin blow by past the rings and pressurizing the crank case

I'd definatly do a compression check on any engine,  It will tell you the condition of the rings and give you an idea of what condition the engine is in.  At 200,000 miles most engines will need some work especially they haven't been taken care of.