My 1987 4.9 easily passed every required tail pipe sniffer test on a dyno from 1988- 2012. After 25 years, it was not required anymore. I still have it and would bet I could still pass a sniffer test today if I was required to. An unfair test because my old engine was held to the same emission standards as all those newer engines at the time..
Not sure how your state does it but I've only had my vehicles tested when I lived in Arizona in 1980. Your vehicles age was prorated by the year it was made. Yours may have had to pass 1987 standards.
At the time I had a 1971 Pinto, with all the EPA stuff removed, and a 1958 Ford with the 223 engine. It was a pretty slick set up. They entered your VIN and the computer printed a sheet of what emissions had to pass at what limits. The '58 Ford sheet was blank.
The Pinto failed. I had 30 days to return for a retest at no charge. On the back of the sheet was possible causes for the failures and fixes.
For the '58 Ford they just handed me a sheet with the print out of the emission test results and told me I was good to go.
So on the Pinto I changed the air filter, spark plugs and checked the timing (actually I backed it down from where it ran the best and back to stock) all which were on the possible causes list. I checked off what I had done and signed the back as self mechanic. Took it back and failed again. The lady wrote a note "failed but improved" and let me go. We had to carry that paper in the car.
Back then it was just a revenue/check a box for the state. A way to get 10 dollars from every vehicle owner.