I just barely passed smog today.At the 15mph test,I had 81ppm HC out of a max of 83, and .45%CO on a max of .48%. For the 25mph test,I had 48ppm HC on a max of 48, and a decent .02%CO on a max of .46%. My 93K mile 1995 Z28 runs great with nothing noticeably wrong. The cat converter is about 20,000 miles old. No check engine lights. I have about 200 miles on a pro valve job.I also have new plugs and Tayler wires, Comp 501 cam,Isky springs,52mm throttle body,1.6:1 rockers,K&N, LT4 knock module,Flowmaster cat back, and new check valves for the air recirc system. The car takes two seconds to start, has a stable idle, and runs like it should be clean. If my cat has prematurely started to fail, I can't tell by any seat of the pants test.However,I am aware that low quality cats with a small Platinum grid do fail in two to three years.I may have one of those.If my timing was on the short side across the board,that would cause higher HC due to incomplete combustion. What product or products can I purchase to check my timing?
When I did the cam,I just saw no marks on any pullies for the usual timing light, so I figure it will be something electronic. If there were something wrong with my Oxy sensor, wouldn't a mil light come on? Or, can an Oxy sensor be "slow" for a long time before it registers as a fault? If my ignition timing and advance all checks out , is the cat converter the only likely suspect? And finally, how would a possible faulty gas cap effect HC ?
thanks in advance for all the replies , Edman

 

There is no way to physically check the timing on an LT1, as the PCM controls both spark advance and retard. The best thing you can do is to get your PCM tuned for all your mods, which can be done by a dyno shop or through MadZ28 or PCMForLess.