Hey there. I have a 84 F150 with a remanned 351w HO that has about 700mi on the motor. Last year right after I installed the new motor, I got the truck inspected (NY) and it passed including emissions, even though the air tube that goes from the smog pump to the first cat was almost rusted completely off. ( i wonder if emisions were even checked) So later, i removed the tube (because by now it was dangling there by a thread) and I plugged the hole in the exhaust pipe. Well when I tried to start the truck, I got backfires right up through the carb (flames coming out of the carb i was told by my neighbor). So my question is was this supposed to happen? Or is it an indication that one or both of the cats are plugged. I ask because I'm starting to get backfires through my carb now when I punch the gas. The carb needs rebuild/replacing which i'm working on getting funds for. I just don't know if this is a carb or timing thing that is going on now or an indication that the exhaust is going too. Thanks to anyone who replies,
Tom

 

Did you plug the pipe that goes to the pump? If not, you might want to try taking the belt off the pump (if possible) or disconnect the tube from it and try driving it. It could be the diverter valve is plugged/inop. If you plugged the tube, open it up and let the pump breathe.

88 F-150 4X4 XLT Lariat w/5.0 EFI 5 spd (DAILY DRIVER)
86 Ranger 2WD w/2.3L EFI 5 spd to be 351W 4bbl C4 (NEW TOY- DETAILS WHEN FINISHED)
85 Old Cutlass Supreme 350/TH350 Holley 4160,Edelbrock Performer intake, el-cheapo headers, General Kinetics 270H series cam, 15.588 best 1/4 mile with original 10 bolt 2.41 gears (OLD TOY)

 

Yeah, the pump belt was disconnected, and the long tube (the air injection tube) basically from the pump to the exhaust pipe was what rusted off. I was just trying to plug the hole left in the exhaust pipe with the whole air injection system off. For some reason, exhaust gas from the engine seemed to be prevented from going through the exhaust system. Thanks for the reply.