im about to smog my 1984 300zx none turbo that im restoriing. what to check, fix, tune,clean for it to surely pass the test? any suggestions? ive already done basic tune ups like oil change, spark plugs and spark plug wires..

Check engine codes. How hard it is to pass emission inspections depends on the state you are in. Some states do only a visual inspections, some like NH don't do it at all for a 20+ year old car, and Cali are bastards about it.

In CT you could just take the car as-is to the test facility, pay the $20 and either pass or fail. If you fail, take it home, do your tune-up within 30 or 60 days, and take it back there again. The second test is free. My '86 Z is exempt from testing because of age. Check with the testing place to see if you have to pay for repeat testing. Around here, mechanics would tell you that if you fail emissions the first time, run the car until the tank is almost empty, add 2 or 3 bottles of Dry Gas and drive to the test again. Worth a try? The testing computers should have lower standards for older cars just to be fair - so if you fail, it won't be by much. They'll give you a print-out of your test results so you can see where it failed and by how much.

so i took her to smog and my precious failed it.. technician said it runs rich.. what should be the cause to fail? i know theres a lot of posible reasons but what are the closest possible cause? it could be the chts, maf and o2 sensor.. anything else i missed? thanks guys!

and when it comes to cars unfortunately im from cali..

Running rich is cause by the o2 sensor. There are different ones for the different model years, make sure you get the right one.

Here are the part numbers;
88hybrid.com • View topic - Z31 engine control computer system (ECCS) interchange inform

thanks bro, i wonder why whenevr i start it up in the morning theres a yellow warning indicator in the middle of my the dash (im not sure if thats a check engine light). but after running it in idle for 30 mins it goes off.. ive been searching net how a check engine sign looks like in 1984 300zx but i couldnt find one. sometimes the warning comes on when i shift from 1st to 2nd gear and when it does it seem like it doesnt give the right/enough power.

Check out this site. It should show you the idiots lights for every dash of the Z31. And tons of info of the Z31.

ZBUM's New Nissan Z31 300ZX Homepage

Nissan Z31 300ZX Warning Lights

A number of years ago I had to change the EGR valve to pass my 88