I had heard that you can use octane boost to lower your emissions.... Obviously it's not something you regularly add to your gas tank, but for the emissions test, you could try it. THat is if you can get it in the us
First, check to see if you have miss firing. If no, ask the mechanic to diagnostic the cat, by either disable the ignition to check the cat cap. to absorbtion, or 2. put the test prob before and after the cat to check the reading, or 3. replace the cat. P.S. co usually causes by a weak cat...email me or post it for follow up here
One more $.02 worth — before the retest, be sure to take the car out on the highway for about 20 minutes of normal 70 mph driving. It clears out a bit of the carbon from stop-n-go and might help you sqeeze through the test. Good luck.
I'd try running a quart of automatic transmission fluid through the system first to help decarbon the head and clean the injectors. Then when you go in to test use octane booster, retarding the timing a few degrees, and making sure it is warmed up good. I don't have get taxed, I mean tested, here thank god, but I have friends who do nearby. Of course that c-note thing always works in CA. My brother-in-law made a ton of money that way.
Wow, you were really very close to passing. Shouldn't be too tough to fix. CO is of course Carbon Monoxide. In a perfect world the carbon in your fossil fuel would combine during combustion with atmospheric air in the intake charge to form CO2 which is carbon dioxide. Relatively harmless stuff that plants use in photosynthesis and form O2. The fact that you are missing one oxygen molecule here should give you a clue to your problem. You are either getting too little air or too much gas. Try cleaning or replacing your air cleaner. Try putting a FI cleaner in your tank. In short, anything that effects how much air or fuel you are getting could cause this. If your injectors are dirty you could be getting a bad spray pattern and this would result in higher HC and CO. You don't mention if the CO is at idle or at higher RPM (some states test at 2000rpm). If it is at idle there is an adjustment on the AFM to increase the air getting through the closed flap. It is a screw on the side of the box. Good luck. By the way, if you want to offer $100 to the smog tech to get your car to pass in California you would need to bring an extra car that will pass as they are online to the DMV when they test you so they would have to tell the computer that it was your Z they were testing and then actually hook up the other car.
fishbine makes a good point about the ATF but I feel compelled to clarify what I am sure he meant to say so that no one goes out and pours ATF in their fuel tank. ATF is just a very highly detergent oil. When I used to run dynosaur oil in my vehicles I would always replace that last quart that burned/leaked with ATF right before the oil change. Cleans things up rather nicely if you care to try it. Do not put it directly into your gas tank. Your car will not run much more than a few minutes after that. On the plus side, you wouldn't need an emissions test!
Sorry Rob, but I meant to do exactly that. Pouring ATF in your gas tank is just like using Marvel Mystery Oil or some such product. I do it about once a year, especially on fuel injected vehicles. It works like a top end cleaner loosening the carbon deposits that can promote detonation and hinder getting a clean burn. ATF has high detergents but is a petroleum product, so it burns. Using 1 quart to about 12 gallons of gas produces a 48:1 ratio, you'll never notice it. It works while you drive, but do it on a full tank.
Just to further clarify, make sure you do run the ATF a tank or two before you go back to test. You want to be running the cleanest gas you can when you test. The ATF will lower your octane rating a few points and produce it's own emissions.