I have recently brought a 1991 Camaro 305. Ive failed the test twice.I passed the Carbon monoxide.But not the Hydrocarbons or Oxide of Nitrogen.

I git the timing correct, new fuel pump(Needed that),oil filter, fuel filter, and that pollution cloth in air cleaner.

I think it might need a oxygen sensory, or distributor cap and more.

Please help dont want to buy unnecessary parts.

 

high hydrocarbons is unburnt fuel, high NOx is excessive combustion chamber temperature, it is weird how those are both high. I bet you have an EGR problem. (not saying change your egr valve) but something wrong with the EGR system. It is worth it to go to a test and repair smog station and have them repair it. They can test it after they repair to see how close it is. and also if you actually posted the #'s you got it would help.

 

The actually numbers are
Required Hydrocarbons 0.80 Required NOx is 2.50
My Camaros were 17.46 My Camaro is 3.80