For the first time ever Retirement Toy failed smog testing! Too high Nox numbers, took her into the shop we use ( very good), & they ran her through again to see the numbers them selfies. Then tested the EGR & all it's components, the cat ( 2 years old, stock one only goes on for testing), & the 02 sensor, all tested good!! Goes back Tue, they think a fuel delivery problem, will test the fuel pump, & if good pull & clean the injectors, & guess they test the regulator. I will change the fuel filter today & checking the timing that I reset back to the stock 5 degrees! This is a pain with my first show next Sat. & still have to redo the door panels, polish out some more & wax her!!
With high NOx, my first guess would be EGR. When you say they tested the EGR and all its components, do you mean off the engine? If so, I would check all the passages. Lots of carbon flowing through there and the passage could be all caked up with it. I've never had a problem with my 20R or 22R engines but when I bought an 18RGU engine, I found that the balance tube, which is connected to the EGR was caked solid with carbon buildup.
Issue is fixed. The TPS sensor had loosen up & moved, this bought the numbers down, also when bypassing a vacuum supply to the EGR the numbers even got better. Going to replace that item & the EGR as both are the stock item from 1988. They will check that vacuum tube for damage or if came lose from where ever it connects.