What would cause a PO174 system to lean bank to code to be set? I recently replaced spark plugs and 2 coil packs. Truck has 129,000 miles. Any ideas? Thanks

 

Exhaust leak or intake leak of some sort. Dirty injectors or fouled plugs. Faulty DPFE sensor or switched DPFE tubes. Faulty oxygen sensors.

Just to name a couple.

I had that code when my driver side manifold had a leak and so I replaced bolts and gaskets and it went away. There are alot of reasons that code can occur though. Most of the time it pops up with other codes though

 

Most common is a dirty MAF or a vacuum leak.

 

Happened to me in Jan. and it was the pcv elbow in the back of the TB. Conveniently had to buy the whole tube w/ elbows from ford

 

issue solved! one of the vacuum lines running to throttle body came undone. thanks for the help guys!