Hey guy's im a new member to this forum but i have read alot of the posts and they have been very helpful, Thanks ! Ok i have a 98 dodge ram 1500 5.9L sport 4x4. I have replaced the whole rear end (Chrysler 9.25 with 3.55 gears ) the intake manifold gasket, IAC twice ,TPS,muffler with a Thrush glass pack. Here's where im lost when i bought the truck every once in a while it would idle rough and the intake would get loud (sucking noise) but no code. So i replaced the IAC. That took care of it or so i thought. Week and half later started to do it again then on morning it started to idle high, 1500 rpm in gear, 2500-3000 idle. So i started looking for a vacuum leak. Found out my intake manifold was leaking. So i replaced that couple days ago. Yesterday the damn thing started to do the sucking noise and idling rough again. This whole time the truck hasn't thrown a single code. I can make it by unplugging something but other than that it no codes

 

Did you replace the plenum gasket while the intake was off?

 

No there isn't a plenum its single piece intake manifold. I did put a throttle body gasket and the pan gasket.

 

If it's a 5.9 yes there is a plenum and a gasket. Known failure points.

 

Ok so i got a better understanding of what the plenum is, it's the intake manifold that is shaped like half a keg "Keggar" yes i bought the intake manifold gasket set. Came with two cross over gaskets the two main gaskets and the pan gasket.

 

The plenum gasket sucks. Literally.

I had mine fixed under warranty and it went out a few thousand miles later.

That time I didn't bother having the dealer do it, I put the hughes plenum plate in.

 

What would be stopping the pcm from throwing any codes? I know there has been times when the truck should have thrown one out for sure. I have to laugh because it is blowing my mind that there isn't a code. Makes me think i have a defective pcm. The truck run great other than it could use little more get up and go power but it won't register a problem and kick the code. What is that all about?

 

If the PCM thinks everything is fine, then it won't throw a code. Even if everything ISN'T fine, and it is getting faulty data, so far as the PCM knows, it could all "Look" fine, so, no codes. Also, in some instances, the PCM really doesn't have a clue what is 'correct' for current conditions, until a sensor pretty much fails completely. Crank and Cam sensors are particularly notorious for this kind of behavior..... they have to pretty much die before the PCM thinks something is amiss.

 

If you get any code it will be a misfire code because the large vac leak causes the pcm to have fits. Get the Hughes kit with fel pro gaskets and forget about it. Had mine for years and not a single problem.
http://www.hughesengines.com/Index/p...p?partid=27091

 

The rough idle/sucking sound is common to a failing O2 sensor. Happened to me a couple times and never threw a code. Then one day it did so I replaced with stock NTK sensors. Nice thing about these trucks is they aren't code-prone like new vehicles. It took 12 years for my first code to ever appear. Have had a total of 3 now for various sensors failing.