Just what the title says. How to diagnose a leaking plenum gasket.

Thanks.

 

Easiest way I know is to remove the air cleaner, turn the butterflies in the TB, and look into the intake manifold with a flashlight. If you see oil pooling anywhere, especially around the edges or towards the rear of the manifold, your gasket is shot.

 

I would pull your spark plugs... my #1 cylinder was completely black.

 

thanks for the quick reply guys. any other suggestions?

 

There's several ways. Checking for pooling oil is one way. I thin sheen of oil is possible as the PCV vents back into the manifold, but pooling is oil coming in from the lifter valley.

A plenum leak will also manifest itself as a rather large vacuum leak. If you aren't pulling a good vacuum (20 inches or better) at idle, start checking for leaks. You can test to see if there's an internal vacuum being created by covering the PCV tube and the breather tube that goes into the stock airhat. NO vac is good.

I'm not sure that an oily spark plug is a definitive answer. It could cause that, but so could a worn piston ring.

 

check the front of the truck, if its says Dodge, then its leaking.

 

there is also a test where you disconnect your PCV valve temporarily,
then add official Chrysler ultraviolet dye to the engine oil,
drive the truck a few days,
then shine an ultraviolet light down the throttle bores
to see if the gasket has let oil leak in since the PCV valve was disconnected

 

hahahaha, isn't that the truth.

 

ok so just looked down my throttle body and found a nice coating of black im guessing oil. There is not really any visible pooling. A heavy residue is inside though. So replace or not?

 

If you don't see oil and it's just black, then I would first try some seafoam or the mopar stuff from the stealer. From what I see on here the early model 2nd generations do not have as bad of a prob with the plenum for some reason. Emission related I'm sure.