Data Transformation Technique Year Percentage change Eviews

[waqaskashif]

hi everyone i m doing research on monthly petroleum prices and i am facing some problems.
1. Non of linear and non linear model provide good results according to goodness of fit.
2. if i use year percentage change transformation technique for making series stationary the further estimations provide good results in each sense so can i use this transformation technique.?
3. what is the manual formula of year percentage technique.?