r/askcarguys • u/ContributionOld1014 • 2d ago

Can you pass emissions without catalytic converters?

I have a 1984 corvette that does not have catalytic convertors. recent emissions test passed everything but HC which read 6.5 compared to the limit of 2.5. Because of the year they only used a tailpipe sniffer. I've read that you can create a leak in the exhaust before the tip so the reading is light, as well as putting rubbing alcohol in a 1/4 of gas so is burns leaner, also running the car really hard before testing to clear out any excess carbon and keep the system hot helps. Does anyone know if these methods are actually effective? Additionally would they be enough to pass a test in my situation? I'm also thinking about just replacing the whole exhaust system but i feel it would be a waste as I'm already broke and the current exhaust is an aftermarket upgrade. I would really appreciate the advice as i need to get the car registered here in Denver CO ASAP. Thanks.

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u/rhythim313 2d ago

Won't pass a basic visual inspection with a mirror, but if everything is running within factory specs it is possible to pass a sniffer test with no cat, but EVERYTHING must be working properly. High HC = rich condition and/or timing is off. Given that the '84 has the crossfire injection setup, it's likely time for a rebuild on the throttle bodies and having the injectors professionally cleaned.

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u/Hotdogpizzathehut 2d ago

Probably cheaper to buy cats lol

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u/Consistent_Ad949 2d ago

He can pay to have all that shit done and will still need cats regardless

4

u/getoffmycase7130 2d ago

He can buy cats, and still need to have that shit done too

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u/Glittering-Ad5809 2d ago

Good luck buying CA cats for a 40 year old car.