It's not a Blazer or an old body style truck but some of the same principles apply. My 93 Pickup is due for smog and won't pass. The numbers on the HC @ 25 MPH are 57 and the most allowed is 50. This is the second test it failed. Last week I took it in and it failed by only 1 point. I changed the plugs and the O2 sensor and also ran some sea foam threw the tank. What surprised me is that is ran dirtier after I did all of that. So anyone have any insight on common problems that would make them high? The CO and NO numbers are a little higher than average but they passed. This stuff is frustrating. Worst part is I have to take the motorhome in this week too. Thanks for any help.