Modifications:
BBK Longtube Headers
BBK Catted X-Pipe
Borla ATAK Catback
Airaid Air intake
Tuned from American Muscle with sct tuner

Hey all. Trying to chase down this issue I am experiencing. Car was running great after all mods and tune file was uploaded for a good while. Only recently did it start having this misfire issue. Pulling codes it gives me these 3:
P219B - Bank 2 Air/Fuel Ratio Imbalance
P0300 - Random/Multiple Cylinder Misfire Detected
P0316 - Misfire Detected on Startup (First 1000 Revolutions)

I've tried reflashing my tune and that didn't seem to do much of anything. I inspected and changed all spark plugs, but the plugs that were in there all looked okay. I checked for vacuum leaks and can't find any. I changed o2 sensors when I installed the new exhaust system since it looked like the sensors on there before had never been changed. I have the BBK extensions for both the front and rear sets of sensors. I'm just at a bit of a loss on what to do next. I sent an e-mail to American Muscle to see if they can look over my tune and see if it needs a revision. Curious if anyone has any other things to check with the given information.

 

run a live data viewing on your SCT while the car is running and take alook at your O2S B1S1 and B2S1 (bank 1 and 2 upstream O2 sensors). The voltage values they present at idle and when you rev and hold the engine at 2K. The values should be fairly close. If not, do you still have one of the Upstream O2 sensors you can swap Bank 2 out with? This will help you see if it's a bad O2S sensor. A lot of times what happens is that the O2 sensor doesn't outright fail, it just gets sluggish in responding so, as your A/F changes, one O2S is fine, the other lags and screws everything up.
Also, how do your Fuel trims looks? Again, LT/ST1 and LT/ST2 (bank 1/bank 2) should be similar and rise/fall together. If not, then the O2 sensor is even further suspect. Fuel trims directly affect your A/F ratio. Those are directly adjusted in part by input from the O2 sensor reading.

 

Oddly enough, when I first start the car the measurements you suggested checking seem to be quite different, though not too terribly different. As I drive the car (5-10 minutes) I can monitor them again at idle and they seem to be much closer together if not identical.

 

Then it's possible that the B2S1 is just slow to respond. It happens sometimes. What brand of O2 sensor did you buy? Unless it's a Bosch or Nippon Denso, most are junk. Bosch makes the Ford OEM sensors

May also want to double check the extension wiring. If there's a bad crimp, it adds resistance to the wires for that O2 sensor and it can mimic a slow responding sensor.

 

I honestly can't remember the exact O2 sensor, but I think it was whatever I could get my hands on quickly. I think they were NTK, but could be wrong. I've heard that my O2 sensor extensions could possibly be the culprit as well. Do you think that is a possibility? Something about some of them being faulty and creating too much resistance that eventually kills the sensor. The more I look into it though, it seems you are probably right about the sensor. I'll have to dive into it more when I get some time.

 

NTK? Never heard of them. Does you Airraid intake require a tune or is one of those tuneless ones? If it's tuneless, I'd put the OEM intake back on. The tuneless Airraids have been known to cause issues on a fully stock car. With your mods it could be running on the hairy edge with being able to control the A/F or not.