Originally Posted by pdudek
I'm thinking to replace the gaskets that are between the TB and plenum just incase and once I install those I'll try your cardboard technique.
A word of warning - this is embarrassing to admit, but I tried the cardboard leak check and ended up sucking 2 litres of oil into the cylinders. I realized when smoke started pouring out the exhaust. So much oil drained into the bank 1 cylinders after I shut the engine down, it hydro-locked them and the starter couldn't crank the engine over. I ended up having to remove the bank 1 spark plugs and vacuum the oil out of the cylinders.
I was well aware of the risk of sucking oil up the plenum drain and oil separators drains so I had the hoses firmly clamped with tools specifically designed for clamping hoses - but the damn clamp on the bank 1 separator drain came loose. So be careful!
By the way, this happened because I took the easy route and disconnected the separator hoses at the valve covers and plugged the hoses. This meant the crankcase was at atmospheric pressure while the separators saw the high vacuum pulled in the plenum. If I had disconnected the separators from the plenum and plugged the holes in the plenum, there would have been no vacuum generated in the separators and no risk of oil ingress up the drain lines. The benefit of hindsight.
Also by the way, I don't believe you can suck oil up into the plenum with the separators still connected because the vacuum pulled in the plenum is transferred to the crankcase so no differential pressure exists across the three drain hoses.
I was worried about the cats being permanently contaminated but I have put a few hundred km's on the car since the fiasco and everything seems fine.
Another thought - with a leak-tight plenum, just before the engine stalls, you could be pulling 15-20" of vacuum in the plenum. That is creating a huge load on the plenum, maybe 3000-4000 lb. Seems to me there is a risk of collapsing or cracking the plenum since I doubt it would have been designed for this.