So Ive done a lot of searches on here and found a few things. On the Dodges a lot of peoples cats have gone and a lot of people have replaced their plenum gasket due to poor design by chrysler. My truck is a 95 5.2 with 93000 mi. The other day I was on the freeway and I went to speed up from 60 to 65 and I got a sort of bogging from the engine. The harder I pushed the accelorator the louder the roar but I didn't go any faster its like I had a huge power loss. Also Ive been noticing when I start the truck in the morning, there is an anoying rattle coming from the catalytic converter, and when I gas it the rattling gets worse then subsides as the RPMs drop. Also at my last few oil changes Ive been burnin about a quart every 3000 mi. Do you guys think I should try and just replace the cat and see what happens or should I go ahead and do the plenum gasket?? By the way I coulddn't find anything on how in depth a plenum gasket install was. It doesnt seem like its very deep in the motor, Ive done a head gasket before so I'm guessing this is less difficult than that. Sorry for the long post but wanted to give an accurate description of the symptoms..
If you are gonna be pulling the intake to replace the gasket I would suggest installing a M-1 intake manifold or a hughes plenum kit. With the M-1 you wont have that plate on the bottom of the intake manifold so there is not gasket to blow and the intake will help out performance wise to. You will get better air flow from the intake. What the hughes plenum kit is, is just a plate that is made out of aluminum. The stock intake manifolds are aluminum and will warp and move but the stock plate on the manifold is made of steel and doesnt warp or give at all so that is why you blow the gaskets. To replace the plenum gasket you have to remove the altenator, compressor, front accessory bracket, and then you can remove the intake manifold once you unplug everything. Also while you are there if you have a stock water pump I would suggest replaceing that and the bypass hose. THe bypass hoses like to leak and can be PITA to take offf if they have never been removed before.
As far as the cat goes. That rattling that you here is the bricks inside the cat coming apart. What you can do to make sure that is the problem is get a rubber mallet and hit the cat and see if you here the bricks rattle. If so then you have a bad cat. I just recently purchased 2 high flow cats off of ebay. I will hopefully be getting them installed in a couple days once I get my headers in and install them.
thanks for the tips guys. So i was going down the freeway yesterday and I started to reach a slight uphill grade and i do mean slight. I push the gas, vrrrrooooooommm sput sput sput slip slip..I lose speed slowly dropping from 65 to 50 in about 1 min..I couldnt go any fatser than 60 the whole way home. Anyhow I get home get out the sawzall cut the cat off throw it on the ground, and all of this white ashy crap comes out and the honeycomb things are all broken apart. I get 2 pipes and fab up a 2 in to 1 pipe to replace the cat weld it in and now it runs fine except when it idles it kind of revs then slows down then revs then slows down. I think this has to do with the fact that I just left the O2 sensor hanging. Where do i get an o2 simulator? Or can I just tap the new pipe I made and screw the O2 sensor in there?? by the way i have a 40 series flowmaster so hopefully my backpressure should be alright with out the cat.. Thanks
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