Hi nox is lean to much air. These aftermarket cats are no where next to the original Volvo cats loaded with platinum pellets. with platinum near 1700 dollar an ounce levels again not sure what they are using these days for a cat that only costs 150 bucks???
I replaced my original cat on my 88 afew years back and the Nox doubled the other numbers were fine, so the cat was not the problem,it was rattling and had failed NJ inspection so I figured it was bad.
I have never had to replace the Bosch heated type O2 sensors on any of my Volvos
70 144 250k
72 145 175k
75 164e 135k
87 240 138 k still going
88 240 127 k still going
92 740t 212k cash for clunkers,cheap shit replacement heater control valve blew out in the Holland tunnel and the wife kept going to get out,once outside shut down and restarted to move it as the cops were on it!!
Blew the headgasket oil in the coolant,still ran great for 2.3 more yrs. Passed NJ emission inspection. What killed it was the oil coming out on the exhaust side between the head and the block,became a fire hazard
Last of the GREAT volvos
Sorry to rant,but it was the AMM that fixed my emission problem,car was running to lean!!!! I had the luxury of pulling a known good one from my 87,which still has the original cat and still passes NJ inspection with no problems!!!