how do I check for a leaking plenum and would it make the truck ping on the Highway, it pings even with 92 octane fuel, on the interstate if I try to get a little more speed it pings like crazy.
the truck is a 98 1500 5.9 2wd, with 103K miles. side note its been sitting for about 1.5 years with a bad rearend, I bought it and replaced the rearend now it wont stop pinging.
thanks.

 

Pull the air box and throttle body off and shine a light in there. If you see oil you have a leak! And yes it does make the truck ping. I put 93 in plus two things of octane booster and it still pings. Make sure you check you oil level. Mine drinks a qaurt a tank!

 

leaking plenum is one cause of pinging, due to lean fuel mix and resulting higher piston temps.
another cause is carbon build up inside cylinder.

a couple of possible improvements
use mopar combustion chamber cleaner or seafoam to remove carbon deposits.
change to a cooler plug. autolite 3923's are one heat range cooler.
replace 195* t-stat with a 180.
use 93 octane gas.
remove anything with timing advance, including Jet Chip module, Hypertech programming, Superchips, B&G pcm, Mopar Perf pcm.

besides the puddles of oil in the bottom of the plenum,
another possible test for leaky plenum is to plug off the main vac lines on each side of the intake, and then try to feel for vacuum sucking into the lines in the valve covers. a few people reported this was inconclusive. i never tried it, as i had puddles of oil.

 

i had the same problem with my 99 5.9. I had an internal oil leak.There was a tsb on it, but i am sorry I don't remember the number(had mine repaired 3 years ago). I took mine to the dealer and showed the service manager the tsb and he knew exactly what I was refering to. They replace the pentilum gasket, cleaned my fuel system and reflashed my pcm. Hadn't had the problem since.

 

This has the TSB number and a bunch of other info and pictures.

http://www.amsoil.com/dealer/techser...num_gasket.pdf

 

so the leaky plenum gasket was fixed in 2000 it didn't look like on the TSB info that it effected any of the trucks built after 2000 can someone tell me if i'm reading this right?

 

Sorry dude, all years are suseptible. I have a 2001 and wouldn't be lucky enough to have a year without the problem. Sorry to bring u down.
Even if Dodge "said" it was fixed for later years, the only way to really know is to look into your manifold with a flashlight. Also,takethe TB off to really get a good view. Of course mine IS leaking slightly, but it doesn't ping or use alot of oil.....yet.