get rid of those iridium plugs, dude.. all those fancy metals will cause you issues.. good ol' copper for those 5.9L Magnums is the absolute best..

if your plenum gasket was toast, it means you've fouled your catalytic converter too- along with the o2 sensors.. o2 sensors being fouled can and will create either extreme lean or extreme rich conditions.. all of those added together will absolutely cause fractures in your valve seats, which in addition to loss of performance due to fluctuating compression, will create hot spots (that literally glow) which will ignite the a/f load before it's supposed to- aka pre detonation, aka pinging..

that dang lower intake manifold gasket (plenum) is the downfall of an engine that has huge potential.. it's a shame how it cascades into all kinds of issues.. but it does.. if yours was truly bad, it could have lit the fuse on all the things your experiencing right now- to include a bearing( < oil escaping the engine via intake and combustion)..

 

Drew Is right even tho i have a HEMI and having a blown head gasket, it threw a few different codes, between misfire, o2 sensors. With all the TECH on trucks now once one thing happens it snowballs problems

 

I bought this truck about a year ago and it has made this noise since i bought it. It started as a little noise now its noticable and it knocks every time i start the engine and while driving. I replaced the plenum thinking it was just that or the lifters which didnt fix anything except burning oil, it really doesnt run better or anything. I did replace the o2 sensors because the engine light came on for the cat being bad. I did pull them and clean them after i replaced the plenum gasket and cat is still bad. I am planning on pulling the pan and polishing the piston journals and replacing the bearings. I did check oil pressure when i first started checking the problem out and it was fine with no problems.

 

the cat ain't just going to repair itself.. it has to be replaced.. the pressure it is likely pushing back on the valves, specifically and most often cylinder eight, where it cracks the valve seats, and fouls plugs (especially fancy metal plugs).. pull that plug and get a look at it..

that engine would have to have been seriously oil deprived to spin a bearing.. say what you will about the 5.9 magnums, but all can agree they are one tough engine.. specifically the rotating assembly..

 

X2 on the Cat if its got a code 9 times out of 10 its done

 

I never said it spun a bearing. I said there was noise coming from a piston main, even that i wasn't sure of. The bearing finally gave up yesterday and im in the process of pulling it so i guess we will see what REALLY HAPPENED. Not to count the cat didn't go bad untill i put a flowmaster dual exhaust on it which made me believe it was never the plenum that messed it up. Common sense about the cat going bad, 5% unefficency sets the code off was what i was told by someone else on this site.

 

Not to count just because the cat goes bad doesn't mean its blown out all the guts it still has the same back pressure, the only difference is the actually filtering affect of the guts in it. I feel it doesn't have a thing to do with the problem i had, not to count i bought this truck over a year ago with the knock when it was so quiet you could barely hear it so what ever happened was before i owned the truck when the cat was good and nothing was wrong but the slight noise

 

maybe on the more advanced PCM of the 4.7/5.7, but never on a 5.9 have I seen a code indicating a bad catalytic converter..

the cat(s) get hot, but not hot enough to cleanly burn oil.. if the plenum was bad, it was sipping oil into the combustion chamber and passing it through the exhaust.. and the cat was catching it.. and it fouls in short order.. a fouled cat creates back pressure on the exhaust stroke, which cracks heads in short order, as well as fouls plugs.. the cylinder most at risk is 8, but seven is at risk too...

another cascade is the o2 sensors- which foul.. they kick the PCM back to open loop, which washes your cylinders running rich, which compounds the catalytic converter problem, which increases the likelihood of cracked heads.. it also creates a situation where predetonation becomes easy, which is hell on internals- piston faces, wrist bearings, rods/journals, bearing caps.. ect.. using precious metal plugs adds to the engines ability to pre-det, which makes it that more likely..

adding any further restriction, such as a chokemaster, likely compounded it even more..

best of luck with the repairs!

 

Yeah dont blame your Flow for jacking with the Cat like i said with these new PCMs onboard one problem usually snowballs problems