My recently purchased 1993 F250 with 351, 4x4 with 5spd is backfiring occasionally when i let up on gas and coast at speed, in fourth gear on a down hill stretch of highway or a bridge. The truck has new exhaust from cat back, the cat is completely empty because does not need emissions. I put in new plugs, wires, rotor, cap, pcv valve. The plugs i put in were the NGK V-Power, which i did not gap - couldn't find my gauge - but was told come gaped from factory. and my timming gun is packed away so never checked that yet. would this be timming or??? the truck runs alot better after the partial tune-up and has lots more power, but still backfires occasionally. but less than before exhaust and tune, any ideas???????

thanks mat

 

It might be like my 91 is, everytime i let off the gas it backfires which is a reslut of me not having a muffler theres not enough backpressure in the exahust system. you might be having the same problem with the cat being gutted.

Just my thought
Kyle

 

Ya, maybe. But I have a 1970 Torino with no cats and dual 2.5 flo pros and have no problem. So I on my f250 I left the gutted cat(last owner did it) and went with 3" single with a short Flo Pro and it exits out the side infront of passenger rear wheel. Pretty sure my old 1980 f250 with 300 6cyl didn't come with a cat and I ran a single 2.5" flo pro out front rear tire too, no backfires??????