I have a 98 ford expedition and I have 2 codes P0171 and P0174 System to lean 1 and 2 can some body please help what this codes mean?

Thanks

That means both sides of your motor are sensing lean condition. I'd be checking for a vacuum leak.

Fairly common codes on Fords. Try cleaning the Mass Air Flow (MAF) Sensor:

https://www.askmehelpdesk.com/cars-t...ml#post1377134