I have a 92 3.9 that kept failing, so (before pushing it off a cliff to put it out of it's misery) I ran it almost empty, put 4 gallons of e85 in it, ran it around town to get it good and hot, then it passed emissions with flying colors. I then refilled it up w/87 octane to burn off all the e85 as best I could. Mine doesn't have the OBDII in it, so it's a tailpipe check for me--not sure if my method would be applicable for people w/OBDII plugs in their truck.