My 95 LT1 has the number seven cylinder spark plug soaked in oil. My blms were at 108 consistently on the left bank and around 130 on right. I changed out the header gasket, O2 sensor, and checked plug wires and coils (DELTEQ).
Can and intake manifold not sealing on one cylinder sue to tear, or whatever, cause oil to get into the cylinder and cause a BLM issue as the O2 sensor will see unburnt oil?

 

A faulty intake manifold gasket will allow oil to be pulled into the adjacent cylinder. But it could also be a faulty valve seal. Large amounts of oil in the exhaust might possibly consume some of the excess oxygen, causing the O2 sensor to think its running rich. But the manifold gasket leak would also be allowing excess air into the system, so its hard to tell.

Did the O2 sensor you replaced have a heavy coating of carbon on it?

 

The header and the sensor were dry carbon coated, yes. But not oily like the plug. I am taking the manifold off here in a couple hours.
The heads have about 5 thousand miles on them. I will check the valves out to see if there is any obvious difference in that cylinder with the manifold off. I didnt check the exhaust valve with the header off. I have teflon seals on the valve stems.
Correction on the valve stem seals, they were K Lines. The new ones I have in hand are Viton seals.

 

Took manifold off, and it seemed dry. The bottom of the gasket had some oil around the intake runners, on all cylinders. All runners were black and just a little shinny.
Put new gasket on. Ran car for a while, with several rpm changes, and it sat for two days. No oil on plugs. I am going to let it set for about 5 days and see if any oil shows up, or any puff of smoke on start up.
If I see a puff of smoke and oil is on one plug, that cylinders valve seals will be replaced, just to band-aid that cylinder and then I will prepare for cylinder heads to be done.
No smoking gun yet.

 

The intake runners are black due to that wonderful invention called EGR. I wish the guy that invented that was shot, Pi$$ed on and burned. In that order. JK.

 

You could also do a compression test on that cylinder, It could be rings.....

 

My EGR hasnt been on the car for years, so I dont think that has any effect on the intake runners.
Also, I did a compression test on that cylinder and the adjacent one. 210 with a drop of 5 psi after 10 minutes, engine was warm.
on the adjacent, 214 with a 4 psi drop after 10

 

Your intake runners are black and you claim the EGR is NOT hooked up. Don't you think that the least bit strange???????

Did you not clean the intake since you blocked the EGR?

 

What do you want me to do, show you that I have an EGR block off plate etc on the back of the manifold? I also did have the intake cleaned prior to the reinstall after I took EGR out etc.
Does that answer the strangeness????????
Here are a couple pics of my manifold. As you can see there are two block off plates on the rear.


And here is my Cylinder head, which was put back together last year with the engine.