5.4 ltr, I put a K&N induction system on my truck. Got an engine lite. Used a hypertech programmer, got rid of the engine lite, but after a day it came back on. Took it to ford, they said the induction system showed lean air in the left bank. Took the K&N off put the stock back on.....no lite. What do I need to do to use the K&N induction system and get no lite?

 

Normally you don't have this problem with a K&N filter. I would double check the fit of the clamps and placement of the intake tube from the filter making sure no leaks. Another thought is to clean the MAF.