My newly aquired POS 88 civic LX 1.5L 16V fails CO portion of emmissions test. Hydro Carbons are OK. Replaced fuel pressure regulator and O2 sensor checked out OK. Any suggestions on what else is causing this. I am assuming high CO means a rich condition.

 

I would chech the obvious, air filter, MAF sensor, and throttlebody(clean it). How do you know the O2 checked out ok? Did you place another O2 sensor(like a wide band sensor) in line with it in the exhaust to compare? That would tell you if there is something wrong with the O2 or the ECU. Oh and just a little hint, don't say POS and follow it by civic around here. People may get offended lol good lick

 

A resistive test was performed on the O2 sensor. I will add another to the system and read it on a seperate stoich gauge in case its an ECU problem. Thanks for your help.

 

It would probably be easier to get a bung welded on and either borrow a wideband O2 sensor from someone, or take it to a shop so they can test it. I am not sure how much that would cost you, but it is your best bet into seeing how well you ecu/O2 sensor is compensating for fuel mixtures.

 

Thats my plan. My brother in law has a sensor and matching bung hes going to put in something else. We'll just weld the bung in mine for now.