My 92 EX auto won't pass emissions, and the cooling fan won't come on (just noticed that one while idling, not concerned with that one, I'm sure it's the thermoswitch or the relay or something). It runs perfect, and the coolant gauge reads normal (except when getting warm, it obviously goes up).

It has all new plugs/wires/rotor, and runs fine. It's definitely not a misfire issue. It barely passes HCs at idle and cruise, but CO is 7.0 at cruise, with a limit of 1. It's rich. I hooked up a volt meter to the O2 sensor (which is a brand new NTK), and it cycles slowly at idle (I'll call it normal), but it doesn't cycle much at 25mph cruise (which is where it fails CO). O2s stick around .70-.80, rarely dropping below .50. There's the problem IMO.

Now my question is, why isn't it cycling? Which temp sensor does the ECU use to get out of warmup (open loop) mode? Is there a way I can figure out what the ECU is seeing as far as coolant temperature?

The transmission does shift OD and the torque convertor does lock, and my understanding is that in warm up mode it shouldn't do either, but maybe that uses a different temp sensor?

 

muffler bearings... have them checked. If they go out, you won't pass inspection.

 

Lol, muffler bearings - those are always a pain to replace.

Anyway... High HC's out the tailpipe indicate a rich mixture. Start by finishing up maintenance items, such as air filter, fuel filter etc. CO is also a sign of a rich mixture. Check and replace all your usual maintenance items and then see if it passes. Ignored maintenance is a leading cause of cars failing emissions tests.

By the way if your cooling fan wont come on, the coolant temp sensor may be unplugged or bad. When the sensor is unplugged it defaults to 0v and tricks the computer to thinking its extremely cold outside. As a result your fans wont come on, and your ECM will richen your overall air/fuel mixture which could be the cause for your high HC's and CO. Intake air temperature sensor may also cause a rich mixture if not working properly.