Here is a post by Al Cline an engineer at Cadillac in the engine division which he did to another board today. He is talking to a guy who has some type of leak. The original question is at the bottom. I don't think Al will mind me posting it here as it might correct some misconceptions like it isn't aluminum but magnesium.
You are looking in the wrong place for the oil leak/smoke/smell....
Understand that on a 93 and 94 Northstar the "silver plastic cover" is actually a die cast magnesium part and it is not just a beauty cover but the top of the intake manifold. When you take it off by removing the perimeter bolts you are looking inside the intake manifold. The oily residue you see is quite normal. It is actually the accumulation of the heavy ends of hydrocarbons from the fuel delivered by the injectors. If you were to remove one of the plastic tubes you will actually see quite a bit of the heavy hydrocarbon residue in the bottom of the intake manifold base. This is completely normal and does not constitute an unusual situation. With the 93 and 94 Northstar intake manifold the injectors, fuel rail, wiring harness, etc. are actually completely INSIDE the manifold. The residue you see cannot leak onto anything.....it is inside the manifold.
In the 93 and 94 the PCV gases are actually routed to phenolic distribution blocks or plates on each side of the intake manifold that act as spacers and isolators between the intake and the cylinder head. The phenolic spacers actually distribute PCV and
EGR to each individual cylinder.
Be very careful to reinstall the cover correctly and torque the fasteners correctly. The perimeter fasteners have large rubber grommets under them to provide the correct clamp load and resiliency to seal the manifold top/cover and the grommets allow the cover to "breath" or "burp" in the case of a back fire to prevent damage to the intake manifold.
On the 1995 and later Northstars the intake manifold is a single injection molded plastic part and the injectors and fuel rail are outside the manifold. The top cover in this case is just a beauty cover/noise barrier.
On the 95 or later the top of the plastic tubes you see is actually the outside of the intake manifold. With the earlier 93 and 94 intake system the plastic tubes are totally inside the intake manifold.
Per your last observation. The "other" PCV tube you mentioned is the fresh air source that comes from the air inlet system There is no vacuum on that line since it is tied into the fresh air inlet system ahead of the throttle blade.
The PCV system works on two modes. At any throttled condition..i.e...when engine vacuum is present.... the PCV system allows fresh air into the engine thru the fresh air tube ahead of the throttle blade. The vacuum at the PCV valve draws the crankcase vapors into the intake manifold to be burned. The PCV valve acts as a one way flow valve with an orifice in the vacuum direction. When the engine is unthrottled...i.e..there is no engine vacuum...the crankcase vapors are free to flow under their own pressure into the fresh air tube and the vacuum side of the system, past the PCV valve.
It sounds like your PCV system is OK from what you said. Double check that the fresh air tube from the non-PCV valve side is unrestricted....disconnect and try blowing into the tube. You should hear the air exiting into the fresh air duct.
The leak you are looking for is possibly on the outer surface of one of the cam covers that is dripping on the exhaust manifold(s). Since the left/front cam cover is relatively open and visible I would assume a leak on the left side of the engine onto the exhaust would be readily visible. Go to the right side/rear cam cover and look with a mirror and flashlight along the outer cam cover joint to the cylinder head. This will be on the backside of the engine, toward the firewall. That is really the only place oil can leak onto the exhaust manifold from the top side.
Get the car on a hoist. The exhaust pipe from the left/front bank to the rear/right bank goes under the engines oil pan at the rear of the engine. A leak from the case halves, rear main seal or and oil filter adapter leak that is following the split line of the crankcase halves can drop onto the exhaust at that point. The pipe should be discolored and show signs of burned oil if the source of the smoke/smell is in this area. If it is then it would be best to clean the block thoroughly with spray cleaner and use the ultraviolet dye test to determine the actual source of the leak.
Just FYI....any "dry" intake manifold will look oily and have deposits inside of the runners and plenum....just most people never see the inside of the manifold because few manifolds let you take the top cover off. A dry intake is a port fuel injected manifold....all the runners transfer or distribute is air so oily deposits can accumulate. A wet manifold distributes air and fuel(as with a carburetor or throttle body injection) and the constant flow of fuel will wash any deposits away. The Northstar intake (as are most any of the convoluted, tuned, individual runner systems) has a large plenum with a lot of "bathtubs" to collect condensed vapors. More conventional cast intakes are typically all down hill to the cylinders from the throttle body/carb. There is a lot of uphill in the flowpath for the tuned intakes to trap condensates. These facts probably explain why the local experts are dumbfounded by your observations.
Al Cline
:Looking for a very evasive, slight, but smelly oil drip in my '94
:Concours, I drove (normally) up a steep mountain grade in an
:effort to locate the source from the smoke from under the hood
nce I parked and shut off the engine. (As a rule, this is when
:it shows up best.) Again, not being able to find where the smoke
:was actually coming from, I removed the hard plastic cover from
:the top of the engine hoping to get a better look. I discovered
:that, underneath the cover as well down inside, around the
:injector plugs, etc. was covered in oil! It wasn't standing, but
:there were a few small puddles, especially in the cavities, etc.
:No one I've spoken with (including our local 'experts') has ever
:heard of anything like this, although I suspect some type of
:ventilation blockage, since the leak is at its most evident when
:the car is pulling a steep grade, which results in a loss of
:vacuum. The PCV valve in the rear valve cover is clear and strong
:vacuum is present. There is some suction from the front valve
:cover port when I remove the tube and place a finger over the
:grommet, but none in the line going to the vacuum source, which I
:assume is normal. Any advice will be much appreciated. I've
:been at this one for months! Thanks!
