I just got my car smogged today and of course it had to fail. it is a 1990 mustang lx 5.0 and the only mods i have done are borla exhaust, k&n intake, JBA shroty headers, ford racing pulleys, and a JET mass air flow sensor. i basically failed the 25 mph test with having too much hydrocarbons (i had a 122 and needed a 96) not to metion i barely passed the 15 mph test (one more hydrocarbon and i would have failed that too. How can i pass smog? Are the parts i metioned earlier (even though they each stated that they were emissions legal for california) causing the problem? Should i remove some of them temporarily or is there anything else i can do that will allow me to pass smog?  

I would suspect if any of the mods you listed, the mass air would be suspect. Thats assuming your running cats, and factory thermostat. Try swapping back to the factory meter. Another thing to consider is the location/mounting of the mass air. I've adjusted air fuel mixture by rotating the meter, sounds weird, but it works.

thanks. ill will definitely swap the new sensor for the stock one .also i bought some stuff called G2P (Guaranteed to Pass) that guarantees any car passing smog. Will it work or is it just bs? 

i did everything including that G2P stuff and i did worse than my last test, way worse. i failed in like four areas this time. should i get new cats or something or what should i do.  

High hydrocarbons is usually caused by a rich condition, or could be caused by bad cats like you suggested, but before changing cats($$$), check your fuel pressure, and tps voltage. It could also be caused by an exhust leak befor the o2 sensors letting in extra o2 and disrupting the readings. Does it smell rich? Do you have any check engine lights? Good luck.

indeed it does smell rich. real rich. like it smells way strong most of the time. also the check engine light comes on sometimes when im at around 1500-2000 in first and second but quickly goes away when i speed up. whats up with that?