Hey guys. Can't find my original "failed emissions" post, so here's another. At this point, I could get the waiver, but that means the truck's next owner wouldn't be able to get one in the future, and it's pretty hard to sell a truck that won't pass emissions.

Problem is CO emissions. Everything else is good. Limit is 25.00. Here's the rundown.

New plugs, cap, rotor. Timed correctly and vac advance confirmed functional.

TEST 1 - HC 2.64, CO 39.29, NOX 2.82

> Changed the oil, coolant, spark plugs, air filter, PCV, thermostat, & raised tire pressure to 35psi.

TEST 2 - HC 2.36 (-11%), CO 31.84 (-19%), NOX 2.71 (-4%)

> Changed O2 sensor (from hell).

TEST 3 - HC 2.54 (+7%), 29.15 (-8%), NOX 3.18 (+17%)

I need to get another 15% improvement to skate by on this one. Not sure what else to do. Truck feels like it's running better than ever. I thought about changing out the temp sensor, which never seems to get up to normal operating temperature, but after losing the alt/fan belt this past weekend, I watched the gauge climb nearly to redline, so I'm sure the engine is just running cooler.

Should I swap in a hotter thermostat?
Should I rebuild the carb?
Replace the cat?

Any ideas are greatly appreciated. Next test, either way, I'll have a bottle of alcohol in the tank and no air filter, but I'd like to get it honest, ya know?

Thanks.