Re: 4.0 backfireing ?
A new exhaust? As in the Catalytic converts? First of all O2 sensors can cause this, as well as a stopped up Catalytic converter. Bad plugs can cause this, cracked plugs, maybe a lose spark plug wire. sticking injector. Being no codes are being thrown and that year of the vehicle, I'd lean more towards a cat. exhaust manifold could have a leak as well. I don't know if this vehicle has a TPS on it or not, but those can cause issues with back firing.
2004 Ford F150 Automatic FX4 SuperCrew 5.4L 3V Triton V8, No Muffler, true dual straight pipes, 3.73 Gears, 18" rims with Wrangler A/T's
White 2004 Ford Ranger XL, Auto, 4.0 SOHC, 4x4 Base Model, 16" Explorer Rims. 3.73 Gears, No muffler(Sold)
White 1997 Ford Expedition XLT 3inch Suspension lift, 38 Firestone M/T's 98 4.6L Police Interceptor high flow injectors, Super 44, brand new rebuilt transmission, with 3.73 gears(Not mine no more)