Ive been having multiple problems with my 2001 f150 4.6. Ever since the temperature has hit the 40s my truck has been smelling like gun powder. I've put my nose down to my tailpipe and its definantly coming from there. I had it diagnosed and it said bank 2 was running lean. I believe it was bank 2. What could be causing this? My exhaust also sounds alittle funny, I have aftermarket magnaflow muffler. But it doesn't sound the same as it did a couple days ago. I've also got a misfire in cylinder 4 so could that have any correlation with the smell/sound?

 

Fix the misfire.

 

I was thinking catalytic converter until you said misfire. Fix that, dumping raw fuel into your exhaust is never a good idea, it will eventually cause problems with your cat and O2 sensors.

 

The gunpowder smell is sulphur. That means yer cats aren't processing the exhaust gas byproducts like they should be - likely due to the misfire(s) - which has also likely by now compromised said cats.

Unaddressed misfires will eventually lead to far costlier damage in addition to yer truck being just plain stanky ...
- raw fuel washing down cylinder walls,
- raw fuel contaminating/diluting the oil in the crankcase,
- raw fuel damaging downstream components like cats and O2's ....

... misfires need to be corrected ASAP.

 

If you have COP's, you just need to replace that coil. And check the vacuum lines- The elbow on the back of the throttle body-coming from the PCV is a prime target for Vac leaks.