Its been forever since I have been on here, but I finally had time to smog my Z31 ECU swapped 280zx to pass smog. It's basically stock except for the 60mm TB, pacesetter header, and cone air filter and intake tube. The original setup always ran lean with high NOX an CO. The Z31 setup on my N/A car runs a touch rich, although I know I have a weak catalytic converter aka "kitten" its still possible to get the car to blow clean. What I'm about to tell you should not be repeated to any government officials or smog technicians, but it works.

To clean the Hydrocarbons up you should retard the timing to about 5deg btdc, and give her some un metered air, like a vacuum hose that goes nowhere or a loose oil cap or dipstick. With this, I was able to leave the MAF properly adjusted and still have a fairly drivable car. Its up to you what you want to do to fool the smog tech on the vacuum advance, I hung a long screw out the cam pos sensor hold down on the distributor and popped a vacuum hose on it and told him to un plug it for the timing test at the TB. also throw some dirt on the crank pulley and repaint the marker so it lines up where its supposed to. All my emission EGR PCV et cetera is how its supposed to be, 300zx vacuum valve on the EGR, and all the sensors are straight up. If you've got a good cat instead of a "kitten" you probably wont have to do most of this. In my mind this swap shouldn't be frowned upon by the state since with a good catalyst its actually way cleaner than stock, but I don't work for those guys. Having a friend that will give you some time on his smog machine is a great help too.

I don't know if I was actually fooling the smog tech, but plausible deniability can go a long long way.

 

Timing is one of the biggest keys to passing smog check on an otherwise "normal" car. My Geo Metro was at 400ppm HC at high speed & almost 700ppm at idle (has to be below 220ppm for both tests). The emissions guy let me "fiddle" with it for a moment. I lowered the idle speed & retarded the timing... BOOM! Passed w/ flying colors.

 

223 ppm? I am jealous. Requirements are a little tougher here at 138ppm HC at 15mph and 138ppm HC at 25mph.

 

i have to tune my car every year for emmisions, making a car idle at 1000 rpms, and dumping the timing to near zero is the best way. run some metyl hydrate also cleans up the emissions quite well. if its dyno run like california and here in b.c. canada (we run calis equiptment and testing) yo should pump up your tires to lessen rolling resitance. the other thing i like to do is unplug the #5 injector. it makes the car run kinda bad, but increase idle to smoothen it out, why #5, well it seems to have the least amount of impact to run quality. doing this makes that cylinder and air pump, it will burn some fuel pulled out of the intake, but thats not enought to matter. as a mechanic ive been getting hi performance cars to pass for 10+ years now. emmisions are just a game and thats how i play it.