I want to install duals (probably straight pipes) behind the cats. I've done this on a 5.0 Mustang, and it sounds terrific! Besides, a V-8 just isn't right without duals. I went to an exhaust shop to have them made, and was told that it couldn't be done, because the 02 sensors had to have backpressure to work correctly, and the check engine light would illuminate, causing problems that would require reprogramming to solve. Sounds hoaky to me. Any ideas?

I'm driving a stock 2001 5.4 4X4, just bought it with 50000 miles.

 

They're incorrect. Reprogramming to solve=retarded. If you can go elsewhere, do it. My shop told me this when I installed a single 3" system with a straight through muffler on my 2000 5.4 F-150. I told them to go ahead and I'd be totally responsible for my own consequences. They were wrong and I drove it for several years without any CE lights.

 

you can easily run duals and if you keep your stock cats, you wont need to mess with the O2 sensors. If you cut the cats out or put in hi flo cats, ive heard that everything will be ok as long as you keep the O2 sensors as far apart as they were stock (on the straight exhaust pipe up by the manifold.)