HC'S ARE UNBURNED FUEL SO IF IT LEAN THEN THEY WOULD BE LOW(LIKE UR READINGS). I HAVENT WRKD IN A SHOP IN A WHILE SO IM A LIL RUSTY BUT I HAVENT FORGOTTEN ALL MY DRIVEABILITY SKILLS. I CAN TELL U HOW TO TEST UR CATS IF U HAVE ACCESS TO A LASER TEMP GUN OR SOME KINDA WAY TO TELL THE TEMP GOING IN AND OUT OF THE CATS.Originally Posted by jfman