i have a 98gt auto. about 80k on the clock. here is my issue, check engine will come on after along drive, an hour or so but only after a piss stop. maybe 10-15 min. stop. now the drive to work is 9 miles one way. my girlfriend will drive it to work no check engine light. she does the speed limit (65-70). when i drive it (80-85) yes i know i am speeding. but no light. the code is for right bank s1 lean. new plugs wires & coils. also 3-stage efi cleaning. have replaced vac lines,pcv,. only things done to the car is aftermarket mufflers & k-n airfilter. ford deal says replace all 4 o2senors & go from there. that is about $400. than still have same code not me. any help will be great. thanks.if this helps 4 fords in one driveway.