not sure if i do or not i just bought an CAI and when i pulled off my stock cleaner it had dirt caked on the inside with the hint of oil .... and here latly when i take off from a dead stop sometimes it is a lil sluggish between 10 and 20 mphs its like the tranny cant decide if it wants to shift up or down could it be a plenum leak or do i just need to tighten my bands on my tranny let me know what yall think i wanna take my truck with my income tax and see bout gettin my 318 bored out to a 404 and drop a stroker kit in it theres a video on youtube of a 99 durango with the 318 bored out to that it sounds so bad....... i just hope i can do it ......

 

THere's a link on here somewhere to the Chrysler TSB describing how to test the plenum. The short of it is you run the engine to operating temp, then shut it off. Remove the breather tube from the airhat and attach a vacuum/pressure gauge to it (10 bucks at Harbor Freight). Unhook the PCV valve and plug the hole in the valve cover, then pull the valve from the hose and plug the hose. Then restart the engine and watch the gauge. If you have any vacuum at all your plenum gasket is toast. If it's OK the blowby gasses should make the pressure slowly go up-- the TSB says let it go about 30 seconds and not let it go over 3 PSI. At 30 secs mine is about 1.5-2PSI.

I do have a little oil on the plenum pan, but since I have no vacuum in the crankcase, I'm deluding myself into believing this is just oil pulled in through the breather and PCV valve. The engine runs great, so... la la la la la.

FYI to plug the hole in the valve cover I used a fired 300WSM casing and a fired 44 magnum on the PCV hose. Perfect fits.

 

+1 ^^^. Also, you can take your air cleaner off and look down through your throttle body with a flashlight. If you see oil puddled in there, she's probably blown. If you only see oil residue, you're probably okay.

 

I have one question that I still don't seem to understand.

where is the oil coming from when the plenum gasket leaks? its just a metal plate, I could understand air.. and what is the definition of the plenum? the plate? its not the keg

 

hey ram 2k1 i looked down my T.B . and all i saw was oil residue no pool of oil thank god

 

the oil is being sucked in through the lifter valley, not in liquid form but more of a vapor form, when the engine demands more air than the intake system can deliver, it has to get it form the easiest place, if your plenum gasket leaks, thats it. so it sucks air (which is mostly hot oil vapor) in through the bottom gasket, it then gets into your intake manifold burning most, but some condenses, leaving a bit of oil sitting on the bottom.
look at the kegger mod thread, it has a few good visual aids for the intake and related components

 

The plenum is technically the entire open space inside the intake. Our intakes are called plenum designs because they have such a large open volume inside them.

The plenum plate (also called the plenum pan or belly pan) is the plate that is on the bottom of the intake manifold. The plenum gasket is the gasket that is between the plenum plate and the intake manifold. The intake manifold is the keg.
The plenum plate sits right above the lifter valley, and is splashed with oil all day long. When the gasket fails, vacuum in the plenum causes oil to be sucked in from around the edges.

There are two reasons that the plenum gasket fails, and I have confirmed both to be true contributing factors.

1) The main reason: The bolt holes on the bottom of the intake manifold for the plenum pan to be bolted to the intake manifold are not tapped deep enough (or the bolts are too long, whichever way you want to look at it). This means that when the bolts are torqued to spec, they are actually only bottoming out in the holes, not actually tightening the plenum pan to full spec. I was told this was the issue by a guy who worked for Chyrsler engineering in the 90's. A guy on another forum tested it on his removed intake manifold and found it to be true. I then tested it on a spare intake manifold that is in my garage, and also found it to be true. I don't know what percentage of manifolds had this issue, but I think it must have been a lot.

2) The secondary reason: The intake manifold is made of aluminum, but the plenum pan is made of steel. When heated and cooled, these contract and expand differently which can cause the gasket between the two to work its way lose. This is allowed to happen even more easily since the plenum plate is not fully torqued to spec because of reason #1 above.

So, by replacing the plenum plate with the 1/4" thick aluminum plate that APS and Hughes sell, you effectively fix both problems at the same time. The thicker plates means you can torque the correct bolt to spec, and the aluminum ensures equal contraction and expansion during heating/cooling cycles.

 

Very nice replys... thanks, that clears everything up. I didn't know that the lifter valley had that much oil in it..

Im gathering parts and fluids I will need for this repair right now. I found another keg at the junkyard, I'll prolly mod it slightly at the same time.

thanks for all the info

I hope I don't forget anything I need.. as I won't be able to go get it once I have started... lol

 

You have to disconnect the breather hose from the air cleaner housing and block it off also. If you didn't do that , you are getting a false reading.

 

I would replace the PCV valve while you're at it.