p1131- lack of upstream heated oxygen sensor switch [ sensor indicates lean bank 1]
p1151-lack of upstream heated oxygen sensor switch [ sensor indicates lean bank 2]
most always due to lazy or faulty upstream o2 sensors. There could be other problems but these codes are usually a good sign of faulty sensors. I would also do a good cleaning of the MAF with MAF cleaner(don't use carb cleaner) the maf is also a problem on these trucks and has been involved in these codes. I would look into joining Ford Truck Enthusiasts good resourse for ford trucks. also here is a link to these tsb that could help, one is for a faulty bolt on the intake that causes a leak and shoots these codes on cold engines. sounds like you might need to change out the two up stream sensors or take a voltage reading to make sure they are heating up and sending a signal to computer.
if the links don't work the tsb's you want go to the top of the web sites page and look for the recalls/tsb tab then click on the full text tsb's and just type in the tsb #'s in the search function, use these tsb #'s 05-22-6 & 01-9-7.
Thanks for all the info I did try to look at other sites but there not as good as this site. I had this problem about a year ago and i made sure there was no vac leaks and reset the computer. It was all good till about a month ago when it came back. The only problem it seems to have is when starting it has to crank for a few extra seconds. I did read somewhere about removing the upper intake to change 2 bolts that seem to be leaking but thats a huge job on this truck. I just thought maybe there was some good ford mechanics on here that have seen this at work.
how many miles on the truck? o2 sensors are considered a tune up item and if they are old they will get lazy, you could get a good voltage reading one day and nothing the next. I still would do a good maf cleaning, remove it and spray it down with the cleaner, don't wipe it or stick anything in there just spray the heck out of it. the intake bolts are a known problem and a cause for leaks, the fix has cured many 1131,1151 code problems. best of luck.