Ok, so this isn't strictly
tech related, but hear me out. After watching this forum for a while I've noticed that the plenum pops up... A LOT
. I have an idea:
What if we all got together and listed the symptoms, consequences, and proper repair procedure of a blown plenum, and then stickied it? That way we would have somewhere to direct everyone to, rather than cluttering the tech page with 5 or 6 plenum threads at a time. It would clean up this forum a lot.
I haven't repaired my plenum yet (think it was done by previous owner), so I cant offer any insight on fixing it, but I can give the symptoms and such.
Symptoms of a blown plenum:
1. Excessive oil consumption
2. Heavy spark knock under load (sounds like a can of marbles when you have your foot in it)
3. Truck feels like it was castrated (loss of power)
4. Trouble getting up hills
1. Clogged cat
2. Clogged cat will lead to #8 spark plug fouling (rather quickly)
3. Clogged cat will also lead to cracked heads (if given time to do so)
4. Fouled front (pre-cat) Oxygen sensor
5. Fouled oxygen sensor will lead to horrible gas milage
6. If given time to do all of the above, the worst consequence: an empty wallet
Why the Plenum blows:
The OEM intake manifold is made of 2 pieces. A steel plate is bolted to the bottom, and the stock bolts are simply too long.
Photo credit to Snowfan. Thank you very much.
How to check the plenum:
Get a good flashlight and, if possible, a dentist mirror. Remove airhat assembly. Open throttle plates and, using the flashlight and mirror, try to get a 360* view of the bottom of the intake manifold. If there is a considerable amount of oil pooling in there, either the plenum is gone, or the pcv is bad. Pcv would spew less oil than plenum.
For a more thorough inspection, remove the throttle body and perform the same check; it will be easier to get a good view with the TB off. Note that you will need a NEW
tb gasket for re-installation if you go this route (~ $4).
As an addendum to checking, and what to look for, This Thread
has pics of various plenums, blown, and not.
This test is to determine if your plenum has already been replaced (by previous owner). You will need a telescopic magnet (available at most tools/parts suppliers). Remove airhat assembly. Open the throttle plates and probe the bottom of the manifold with the magnet. If it sticks on the bottom, the plenum plate is OEM, if not, it has been replaced with an aluminum plate (which means it has already been fixed). Credit to Saber6
for suggesting this.
How to check your CAT:
Driving with a clogged cat is very bad for your engine, so I have added these ways to check your CAT's performance to this guide.
Usually, the first indication of a clogged cat is #8 spark plug fouling (I.E. you pull plug #8 and there is a lot of carbon, but the other plugs look good[ish]) after that, the truck will "chug" under load or when going up hills (feels like a dead miss). Under some circumstances, a clogged CAT will set a p0420 or p0421 code; and the CEL may flash at you to indicate urgency.
1. Take out the pre-cat O2 sensor and take it for a drive (note that the truck will be louder, this is normal). If the truck feels considerably more responsive or has less trouble getting up to and maintaining speed, there is a good possibility that your CAT is clogged. Note that driving without the O2 sensor will cause the CEL to illuminate. Just clear the codes (reset the PCM) afterwords.
2.Drill a quarter inch hole before the CAT and insert a pressure probe. Any reading over 2psi indicates CAT failure. Here's a vid that details it better:
Credit to HeyYou
for the information in the above section.
Best replacement (from what I've heard):
Plenum kit available from hughesengines.com OR
Make your own: https://dodgeforum.com/forum/2nd-gen...num-plate.html
(credit to purpl on make your own)
Links to a good write up on repair:
Credit and major props to dhvaughan
for this link. Seems to be more complete than #2.
Credit to Agostage
for providing this link
's self described "terrible video" (LOL) on plenum repair:
When repairing the plenum, it is not advised that you re-use the stock intake manifold bolts. They are tty (torqued to yield), and may (probably will) snap upon re-installation, or may cause the intake manifold to not seal correctly due to bolt stretching (which would constitute a large vacuum leak).
Hopefully this thread will catch on. If I've left anything out, please post with the info, and I'll edit to add. I'll need someone to post with proper repair procedure (preferably with pics) so that this thread will be complete.