ok so i added some mods to my hd.. cold air, single blade throttle body, upper plenum, exhaust(no cats but o2 still in place), msd coils...when im stationary but set in drive my engine is sputtering and the odd time it does it while WOT, everything was working mint before these mods were done.. is it the fuel/air?? coils? all i know is that i need to have this fixed before i put the pulleys on and slap it on the dyno... oh ya and my exhaust reaks like burning plastic.. its a full bassani stainless... is that just stuff burning off the pipes? lots of black sut in the pipes aswell.. I need to get this fixed PLEASE HELP ME EVERYONE thank you

 

What year and engine size? The lack of cats is leaving unburned fuel in the pipes. As soon as the O2 sensor realizes this, it tells the engine to lean out and cut back on the gas. I'm thinking that's your problem. The only way to fix this is to get your PCM flashed so that it doesn't recognize any of the O2 readings, or get some high flowing cats.

 

its a 5.4 sc same as the lightning 2003.. i turned the cats off and the same thing happened

 

Turned off the cats on the PCM? Maybe you didn't do it right.

 

um well how else do you do it lol.. its either on or off.. i have an sct tuner.. you may be right but i have tried everything maybe i should get for to throw it on there computer but it costs an arm and a leg there

 

Id go and buy a set of magnaflow hi-flow cats and have them put back on. It won't hurt your performance, peak performance, and it might make it sound better too. It will cost less to have them installed then to have them reprogram your PCM.

 

I don't think so. The upstream O2's are *BEFORE* the cats and they control the mixture. All the downstreams do is monitor the cats and don't control anything - all they do is set a CEL when they detect low efficiency.