At 30mph when i floor it and the truck downshifts, it some times backfires now that I got my intake and its been cold out. Will a tuner fix this? or is it something else? What is causing the backfiring in the first place?

 

Read:

http://en.wikipedia.org/wiki/Back-fire

 

ha... my Dad's 85 F150 would do this (back in 1998)... it was fun for awhile, but then he had it tuned and it fixed the issue. That was clearly a much older engine design, but I believe the adjusted the timing and did a general tune-up.

You could sure wake people up with it though. It was a stick-shift so it was really easy to make it back-fire (or after-fire) when you wanted to.

 

you might have an injector or 4 sticking. A backfire is caused by unburned fuel going into the exhaust. You could also have a bad COP. Check out my posting about bad injectors, broken plugs, etc at 30k miles.

 

uh, a backfire can be from a lean issue as well my friend