I have a 81 that recently had a motor change from a 80 RX-7 with 50k on it. It runs fine but won't pass smog. All of the 81 smog equipment was attached to the 80 motor with the extra air ports on the block blanked off. I have the readings at idle and high speed. I wonder based on the readings, can anyone tell me if I need a cat, carb, etc. It has been tuned up recently. Here are the readings: AT IDLE; H.C. 650ppm, CO% .70%, CO2 13.60, 02 .96, NOX 58PPM... High Speed; H.C. 340ppm, CO% 1.10%, CO2 13.10, 02 .96, NOX 68ppm... I really don't want to get rid of it, it's really clean, and runs well, but just won't pass that dam Ca. smog...thank alot...Mike

 

When was the last time the cat was replaced?

 

about 10-15k ago...It was the same cat after market single (took off the other one years ago with no smog problems before) that was on the car when the first motor blew a Plate (head) gasket...

 

Couldn't have blown a head gasket, but maybe an oil seal or apex seal maybe?

Make sure the carb is tuned correctly. The Haynes manual has a good description on how to tune the carb to meet EPA standards.

 

Check your air control valve....

Mine is shot do I put a cork in the retun to the air filter. All the air now has to go into the cat, making a better burn.

check it out, It's worked for me 2 times now....

 

breesej is right. But you should also pull out the diaphram if you do this. And be warned, it will pass like new car if the cat is still good.

Ryan

 

So what are the limits for your No and HC? Which one is failing? Those numbers look good compared to what my last car passed at. I think my MX-6 was good at 1000 and 250 for HC and NO, so I can't understand why your failing?

 

Whoa 1000 ppm and they pass it??? I and I thought CA was the smog-**** state. Here they'll fail ya with over 220 ppm HC. Of course the visual isn't as tight, and the people I go to let me superheat the cat (try reving it to 4k, and keeping it there for about 20-30 min, right before the inspection, or go for a nice long drive) I got my 85 to pass with 127 ppm HC at idle, and 15 ppm at cruise on a dying cat (it cracked and clogged 2 months later), I don't remember my CO, but it seems to be about what you have.