? for anybody that's looked inside their plenum
 

I removed my stock upper plenum this weekend. As expected, the inside was slightly greasy from the oil fumes recirculating back through the intake. I've seen a number of people report the same.

The thing that concerned me a little was the "gooseneck" part of the plenum. It seemed to be covered in a thin layer of black soot. I have always noticed a fair amount of black soot buildup on my exhaust tips. I assumed I ran rich because of our hot, humid LA weather. Now I'm wondering if I'm way too rich?

Has anybody else noticed a buildup in their plenum?

I'm thinking of doing a couple dyno runs to see what my real A/F ratio is. Good idea or useless?

BTW, I'm using an AAM tapered spacer so I thought that would have cured some of the richness problem with the front two cylinders.

When I asked the service manager about it, I was told there were no adjustments that could be made to the A/F mixture. (probable BS). Unless the engine throws a CEL, they won't even look at it.

Thanks,
Dave

hmm.....i didnt have any sort of buildup on the inside of my plenum...i only had about 4k mi...but still.....you sure you didnt have a leaky intake or a dirty filter?

what does the oil have to do with your A/F?

that oil is normal. It's not great or anything. It can lead to possible detonation - nothing to worry about for NA really though unless it's REALLY REALLY bad. Never hurts to clean it up every couple years or so though

I've got more miles - 13K so maybe you didn't have enough time to get much of a deposit.

Filter's clean. If I had leaks in the intake, I would think it would run like crap.

The oil has nothing to do with the A/F. It's normal and I expected it. I didn't expect a soot/carbon buildup. My train of though was that if I was running real rich (causing soot/carbon buildup on the exhaust), then some of the blowby that recirculates from the block back through the vent tube in the intake was causing the buildup in the plenum. I thinking I need to see if my A/F is significantly rich if this kind of buildup is not common in other plenums.

This is what mine looked like.
23K miles
The specs and stuff is from debris from sitting on the garage floor. The oily film is what was inside originally.
This what yours looked like?

That's pretty similar to what mine looked like. More dark stuff in the part where the TB mounts. Can't take pics as I already cleaned mine and sent it off for polishing.

The oil is from the positive crank case ventilation (PCV). The hose that feeds into the underside of the intake tube pulls in some amount of oil. Its normal. You can use a catch can if you want to reduce it. This is especially good if you have forced induction as you will have greater crank case pressure and more oil.