short story . in 2009 when I did the tailpipe emissions test here in utah
my HC {PPM} was 14 at 15mph and 29 at 25mph
this was with the original factory y pipe, cat, and exhaust .
.
the whole mess from y pipe back to chrome tip rusted out and had to be replaced last Sept ,first step was a factory equivalent cat-back than 1 month later a warp-speed y pipe and cat man cat,.
now this years emission test done today had the %Co2 as the same as last year and the NO{PPM} same as last year but the HC {PPM} jumped to 87 at 15mph and102 at 25mph with the max allowed at 121 and 112 respectively,
can removing the pre-cats and changing to a generic Cat be the reason for the jump in HC ? I have no codes and no other problems but putting the OBD2 scanner on the car right before the check did say the cat was not ready , but again no codes. the o2 sensors all 3 of them and the cat are new.
1 more thing i drove the car 20 miles on the freeway before the test. and idled in the parking lot at the test place for 30 mins, IAT hit 140F and the Coolant temp was 198F

 

if u have a hi-flow cat, then it will be very hard to pass emissions. Y-pipe usually has nothing to do with emissions.

 

The pre-cats only do their thing right after start up, before the main cat has a chance to warm up. I have a y-pipe and a stock cat, and my numbers are very close to stock. The reaction in a three way catayst produces heat itself, so a low volume of gas flowing (idling) could cause it to cool. Heat, being a catalyst itself, promotes the reaction to occur. So low heat = not a vigorous enough reaction. This is probably why your system showed that the cat was not ready. However, it passed, so you are in the clear. Next year, try to drive your car straight from a warm up session to the emissions machine. The cat will be hotter, and your HCs should be lower.

 

Yo AJM,

U got a 97 right, so then for emissions all they do is hook it up to the scanner. U dont have to worry about the numbers? I know thats how it is in MAss

 

You know, now you have me wondering. Maybe it wasn't that my numbers were almost stock, just that I passed. I do remember getting numbers though, but maybe it was for a different vehicle. I don't commit too many of the inspection details to memory. Pretty much just a do it and forget it thing. Either way, the y pipe will not make you fail emissions.