I have a 1990 w150 and just installed headers and a 3 inch exhaust and a lean code is showing. Any help?

 

did you try disconnecting the o2 sensor?

 

I replaced the o2 sensor because it was old. no change. Is 3 inch tubing too big and producing too much air flow for the o2 to get the right readings. I have a buddy that has 3 inch straight pipe and his runs perfect. ???