Hi all.

Just had an emissions test and the stock 1996 Honda Civic LX failed with a High CO reading at idle. HC and NOX were very good but the CO failed the Idle test. CO allowed "1" my result "1.78". 40km/h test (25mph) results were a little high as well, allowed is "0.42"ppm my result "0.40"ppm. The high CO is a suspected over rich condition. I've done the Injector idle check, remove electrical lead and listen to idle drop with all 4 being the same. Just wondering if anyone has any good suggestions to help isolate the cause. I did a complete oil/filter, plugs, leads, cap, rotor & KN air filter replacement. I did put a little too much oil in but don't think that would have any effect to a high CO reading. Could be an EVAP problem or fuel regulator but was wondering if anyone has had any experience like this at all.

Thanks for your time

 

if fuel delivery is what is causing the failure(to rich) I would suspect a few things. Lack of air delivery or capability, like a bad air filter. Another thing that would affect it would be a bad/dirty MAF sensor. You have already replaced the air filter so that is done. As far as the MAF if you don’t get a CEL then I would say just clean it. These sensors are very delicate so you have to use electrics part cleaner in a spray bottle. They sell it at most auto parts stores. I use the CRC QD Electric parts cleaner. Make sure you just spray it with the cleaner and let the cleaner do the work. No abrasive cleaning pads or anything like that. Then you let it drip/air dry. Unplug the ECU fuse or battery for a few minutes to clear the mem and make the ECU relearn the new signals faster. Make sure you drive it for at least 200 miles before any emissions test after you cleared the mem. Next I would look at the 1st(the one before the cat) O2 sensor. This is what controls your air fuel mixture. The O2 sensors are replacement items and cannot be just cleaned off. I’ll leave that to your discretion. However, O2 sensors operate when they are brought up to temperature properly. I would say if you went to the emissions test after the car had been sitting for a while and didn’t drive it more than about 30 minutes, it is possible the sensor was not warm enough at the time of the test. Always make sure you drive it medium/hard for about 20-30 minutes before the test. Also if it is sitting for a long time in the parking lot while you wait for the test station to become available, make sure you tell the tech to warm it up before actually going through the test. They should know this, but most are in such a rush that they don’t do it and really don’t care since they still get paid. I hope this helps.

 

97 CivicEX,

Thanks for all your help and suggestions. I received a conditional pass due it looks like the ecu is bumming. It is not adjusting after receiving the signals but it isn't giving a CEL light either. The CO readings got down to 0.12 40kph test (25mph) PASS but still failed at idle LIMIT 1 my reading 1.37ppm. We swapped out a working O2 sensor, cleaned the MAP, full tune but there was some funky stuff going on with the ECU, strange ground signals. Well I've got the pass and now I've got some wiring issues I'll have to chase down. The end result may most likely be a new ECM/ECU. Again thanks for your help.