ok i got a 360 and my factory cat was getting plugged up from my blown plenum. i will be replacing that here in the next couple weeks when i get my brother 2006 dodge for a while. i plan on doing alot of work while i got his truck. but right now im driving mine and i cut the cat out because it was getting plugged up.. i got 215xxx miles and add about 350 every week. but with the factory cat and a single in dual out thrush welded muffler i managed to get 16 mpgs on a long trip up north and usually average 14.7 city/highway.

so i cut the cat and now im getting 12. i bought a magnaflow y pipe and installed that. i cut pipe off the back of the cat that had the o2 bung and put the upstream o2 in that bung and put that right after the y pipe and just tied the downstream to the frame. i thought i would get a little better by getting rid of the cat. but im getting worse.

what is the best way to set up my exhaust so i get my good mileage back??? the truck also is all stock. 360 5spd 4x4

thx matt

 

The Y-pipe should have had a spot for the pre-cat O2 sensor in pretty close to the original position. Placing the sensor further back gives the exhaust some time to cool/disperse, so you aren't getting really accurate readings from the O2 sensor.

Did you reset the PCM after making those changes?

 

Ok I picked an o2 bung to weld into the y pipe. I will do that herein a bit. To reset the pcm I disconnect the battery, correct??

 

Disconnect the battery, turn on the headlights for thirty seconds, turn off the headlights, hook the battery back up. Quick, painless, and easy.