Today was my third try at passing emissions and I failed once again. My test results were HC 618 with 53 allowed and CO 0.98 with 0.28 allowed. So far I have replaced the cat converter, plugs and wires, O2 sensors, coil and control module, header gaskets, opti spark, ecm. I'm running out of options real quick because my registration expires in 4 days and won't be renewed until I pass. My car is a 94 Z28 with 79000 miles and I thought in great shape. Any and all ideas will be greatly appreciated. Thanks

 

Have you checked the fuel system, ie fuel pressure, injectors, fuel filter?

618 HC it's running way too rich.

Was the cat just replaced or awhile ago? You may want to recheck it.

 

Thanks for the reply. I yesterday replaced the cat again w/ a known working unit, and checked fuel pressure..42 lbs. Retested and got even worse results...HC 913, CO 184. I ordered another set of o2 sensors because I always get the 4 wire setup, which I'm confident that I wired correctly. Hopefully I'll get a 2 wire setup this time. Again guys I'm desperate I have to pass to get my reg renewed. Please help

 

did you have 160* or the stock tem? what are the fans set to come on at? has the ecm been retuned?

 

Once again thanks for the reply 180 thermostat, started at 160 Hypertech... PCM tuned to my cam and start fans at 180. I going to have to sell my car if I can't figure this out.

 

I had troulbe passing when my fans were set at 200. The hotter setting would help heating up the cats. setting to fans back to stock would help, but i bet the tune you have is running a little fat..

 

I have heated O2 sensors...thus the 4 wire, shouldn't that semi correct the problem? Once again thanks for the reply. Please keep giving ideas. Thanks

 

heated O2s do not heat up the cats. it is only going to being the O2s up to operating temp sooner.

 

Why do you want to run a 2-wire sensor, and why did you have to wire the 4-wire sensors on your car? Its already set up for 4-wire sensors.

What are all the mods to the engine? You mention headers..... what else?

 

I have no idea how emission testing is done since I live in MI, otherwise i might be able to help you.

Have you ever passed with this cam? and has it ben tuned?

 

Once again thanks for the advise and sorry for the late reply. Well after getting my car scanned the garage concluded that the optispark (new) and the cat was bad. So once again I replaced the optispark and cat with BRAND NEW parts. Guess what? I failed again but got closer, HC 490 and CO 1.97. Today I got the car rescanned and everything looks 100% yet I still failed.
As for the 02 sensors my car originally had only 2 wires running to the sensors for the unheated version of 02's. My car has the same mods it had before when it always passed no problem..biggest mod would be the hot cam..everything else just basic bolt ons.
Thanks