Thanks for all you responses. I did use the spacial O2 socket and broke it, but did not access to mapp or Acetylene. Bottom line, do the O2 sensors need to be replaced if you have over 100k miles? Is there a definitive test to determine if any or all 4 are bad? I just had the most recent codes read and they are PO131, PO136, PO156 & P1131. What upstream test could I do to detrermine the cause of the codes tripping?