so last week i took off my throttle body and cleaned it all up and replaced the IAC on my 2001 3.9 because it has been idling bad lately. it also knocks, has been for years. anyway, i took a flash light and looked down into the intake manifold and my worst fear came true. it was covered in a yellow film of oil. is this the reason my truck knocks and idles bad? would it be easier to change it myself or take it to the stealership? anyone done it?

 

Does it knock just sitting there idling? Or does it spark knock when accelerating up a hill or under a load. If it does it up a hill or with a load then yes, that's probably it. Otherwise probably not.

You can do it yourself. Just make sure you buy a good plenum gasket, and you'll also need to get the intake manifold gaskets because you must remove it. And a tube of RTV high heat sealant. It's a pertty straightforeward job, just takes time. Figure in about 3-4 hours to get the job done.

Here is a good How-To on replacing the plenum gasket. http://www.v8performance.com/Plenum_...eplacement.pdf

 

i only notice it knocking when sitting there idling. i have noticed it knocks worse when the engine is warm. ive been thinking about getting a colder thermostat, but i think that would only cover up the problem instead of fixing it. i thought that if there was a film of oil in the manifold that the plenum gasket was bad? or is it normal?

 

if its just a light film of oil on it, then thats normal. but if theres a puddle or a heavy film on it. then the plenum is gone

 

i think it was just a light film of oil. definately no puddle. i still cant figure out why my truck idles like crap though.

 

Man this forum is the greatest find ever

I'm thinking the plenum gasket on my dakota is causing me issues as well. I've been getting really bad milage (14 mpg highway city mix, down from 17.5), and when I looked down the throttle body, I couldn't help but notice that it was REALLY dirty in there. I'm relatively certain given the reflective surface appearance of the grime in there, that there's oil leaking as well. At the very least it's extremely dirty though.

I figure i may as well just take the whole assembly apart, clean it properly and thuroughly, and replace the plenum gasket while I'm in there. My truck does have 130,000 miles on it, and it was poorly maintained before I got it. I remember pulling out the air filter and it being so dirty the guy must have hit a cat or something, haha.



Anyways, just some quick questions:

1- That informational document mentions that the plenum gasket should be tightened to a specific torque. Is it okay to just go in there and tighten it proper, without doing it to a specific torque, or is a specific torque really important?

2- What is the "Fuel System Pressure release procedure"?

 

1: You can pretty much just tighten it by feel, just do it in the order described
2: Basically, just unscrew the little plastic cap on your fuel rail and push in the shrader valve with something like a small screwdriver(with the key off of course) This will release the fuel pressure in the rails. Careful though, put a rag over the valve before you do it and watch your eyes. Fuel will shoot out when you do it.

 

Thanks for that info. I just finished changing the plenum gasket. MAN That was a fiasco!

The directions seemed a bit off though, hehe. They emphased the gasket change, when they should have put more informaiton on the dissasembly process to get to the manifold. THAT was my huge fiasco!