Emissions help please

[Shangsta]

My car just failed emissions twice in a row now. The car is a 91 318is that has always passed with flying colors. I have not changed anything since the last time it did emissions although it has been sitting for the last month not being driven. It is failing on the NOx. The first time it only failed on the 50/15 test with a 1324 and the allowed is 1134. Talked to a friend and he said since the car has been sitting for a while that maybe i didnt drive it enough before the test. Well I drove it for an hour, on the highway and city driving and it failed even worse and on both the 25/25 test and the 50/15 test. Anyone have any idea of what I should be looking for. Was going to be doing some projects on the car so I didnt need to get it tagged but now somethings come up and I need to use it as the daily for a little bit so I need help. Thanks

Here is the numbers

25/25 test
reading allowed result

HC ppm 102 141 pass

CO % .37 .79 pass

NOx ppm 1254 1026 fail

RPM 1973 3000 max

CO+Co2% 14.64 6.00 min

50/15 test

HC ppm 102 146 pass

CO % .38 .82 pass

NOx ppm 1671 1134 fail

RPM 1878 3000 max

CO+CO2% 14.64 6.00 min

[jlevie]

I'd suspect that either the engine is running lean (intake leaks or a fuel delivery problem) or that the catalytic converters are gone. It probably would not hurt to run the gas out and refill with fresh.

[JinormusJ]

It's the cat

Only thing that monitors NOx emissions on our OBD1 cars is the cats: not passing strictly because of NOx is almost always the cats. Believe me, I've tried everything to get my e30 to pass because of NOx (Smoke test; running valve cleaner, injector cleaner, intake system cleaner, Octane booster, fuel system cleaner, oil change) and nothing worked until I replaced the cat