Hey, need some help from anyone who's had similar problems since I'm about to lose my mind with all the repairs I've made chasing ghosts. I've saved quite a few bucks reading DIY threads on this forum, so I appreciate what you guys have already posted.

Problems:

1. Had the transmission rebuilt, but had to bring back to the mechanic four times for overdrive light coming on (usually 100 miles into trip or around 1-2 hours of interstate driving at 65 mph). I believe it's the torque converter overheating, but I've had the mechanic disassemble four times, same trouble, new torque converter didn't help. Replaced the TPS sensor, didn't help, but seems to run better. I have an external transmission cooler without the check valve. Also, once in a while there’s a grinding noise when lightly pressing the foot peddle around 45 mph, before the transmission down-shifts or up-shifts.

2. Had the plenum pan / gasket changed a year ago by the dealer, who replaced with a metal gasket. Trucks been eating 2 quarts of oil every 300 miles last 6 months. I took off the air filter housing, opened the butterfly on the throttle body, and found oil residue. There's oil residue in the PCV valve and the line running into the intake manifold. But, there’s vacuum pressure. So is the plenum gasket bad? Should I slap an aluminum pan in (APS or Hughes)?

3. I replaced the catalytic converter a year ago, which is what blew the plenum gasket originally. Is there a way to check the differential pressure on the catalytic converter to see if it’s still good or partially plugged so I can rule it out? I seem to have decent flow out of the exhaust pipes, but I'm not sure.

4. Exhaust valves rattle somewhat when the engine is under load (going uphill). Is this related to the O2 sensors / MAP / TPS, or do I just need to replace the valves, rocker arms, etc.?

I’ve replaced just about everything that’s possible to replace on this year model. Any help or advice is greatly appreciated.

 

1. hope you have a lifetime warranty on the trans. it sounds like you're going to need it. sorry, i can't help here.

2. that's a lot of oil being used. some oily residue in pcv and hose is normal, since vacuum sucking on pcv is picking up oily air. if the plenum is leaking it will cause you to lose oil, also it causes the engine to run lean, and ping (see #4). if the plenum was repaired 1 year ago and it didn't use oil bad after that repair, and now its using oil like crazy, and its not leaking it, i'd guess that the plenum gasket is leaking again. if you can swing it, fix it with any one of the aluminum aftermarket belly pans. it will fix it forever. i can't understand why dodge can't understand that. one test is to remove the throttle body and look down in the plenum, especially in the rear since the motor is tilted back. a big puddle of oil is not good. you can clean the tb while its off. another test is to disconnect pcv hose from manifold on drivers side. plug manifold port (with rubber cap)and pcv hose (with a bolt). crank truck. now remove the hose between pass. side valve cover and breather, at the breather. is it pulling vacuum ? it should not, and if it is, then the plenum is sucking air.

3 i don't think a plugged cat can affect the plenum. if its only a year old its probably fine. i've heard you can test with thermometer, but i've never done it cause i don't have access to a fancy thermometer. pipe temp should be higher after cat if all is well (i think).

4. the rattling sound, or pinging, under load is actually not the valves, but the sounds and vibrations of pre-ignition, which is terrible on the motor. you need to either fix the cause, or use premium gas to get rid of it. pinging is caused by the fuel mix exploding under temp and pressure before the spark sets it off at the ideal time. by exploding early, its causing the engine to work against itself. ping can be caused by a large number of things including advanced timing (hypertech), carbon buildup which holds heat, and lean fuel caused by plenum leak. simple things that MIGHT help are cooler plugs (autolite 3923), 180 thermostat, seafoam cleaning. simple, but expensive thing that will USUALLY help are premium gas. premium gas helped me coverup the problem. hughes plenum fixed the problem.

 

Thanks for the advice, I appreciateit. I'm going to try slapping a new aluminum plenum in and a couple of O2 sensors and see if that works.

 

I'd hold off on the O2 sensors. Stick to the plenum replacement and see what that does. Don't forget the intake gasket/bolt set (if you get the Hughes replacement).

You can always R2 the O2S later ... if you need them. They can be cleaned up pretty easily, too.

There's only one thing that eats oil that fast (without you seeing it on the ground) and that's a blown-out plenum gasket. Consequently, it usually also causes massive pinging. With all the oil you've burned, you might need to give it a good Seafoam/MCCC treatment as well (if the pinging doesn't stop).

 

Can someone describe to me what the plenum is? I don't know if I know it under another alias, but it sounds like an awful part to have go bad... Good luck with everything.

 

It's also known as an intake belly pan. It mounts to and seals the underside of the intake manifold. If its gasket starts leaking, the vacuum from the intake sucks oil out of the lifter valley and routes it (of course) into the cylinders.

 

pull off the TB and look down into the intake with a mirror & flash light... check all 4 corners to see if you have oil pooling on the bottom of the intake... if it is, the plenum gasket is leaking. looking straight down may not be good enough to see oil getting in. 2 quarts every 300 miles is alot of oil, is it blowing blue smoke? leaking anywhere?

If you do have to do a plenum swap, make sure you use the felpro gasket and new plenum bolts. it is highly suggested that you used the aluminum cover from APS or Hughes.