i got a 05 f150 fx4 with a 5.4 engine, its got a k&n drop in air filter and has two cats with true duals with no mufflers running out the back, when i floor it, it will like start misfiring and im wondering if anyone knows what might be causing it, i used to have flowmasters on it in the past and it never did this so i was thinking maybe its because im running it with no mufflers? also, the cat light came on and started blinking but went off after a minute.

 

How many miles is on it? Good be time for some maintenance. Plugs, MAF cleaning, throttle body and intake cleaning. You do oil that K&N drop in right? If not, you are letting in too much debris and contaminants, if your over oiling it, your MAF is getting gunk covered and dirty.

Did your 05 originally have 4 cats? Or does it have 2 cats factory? ( Every truck built jan '05+ has only 2. )

As far as I know, there isn't a cat light in the cluster, the only way a O2 sensor issue can appear is with a basic CEL.

 

53,000 miles is on it, and yea i clean and oil it when it needs it, i looked at it and it looks good, it came stock with 2 cats, and the light that came on was the one that saids in the manual that a misfiring is happening and can mess up the cats

 

Sounds to me like you need to clean your MAF.