1993 Civic Fails NOx

I have a 1993 Civic with 1.5L, 16V SOHC engine, 156,000 miles. I took
it for an inspection and failed NOx, the limit was 2.00 gpm and the car
registered 2.64. The HC (0.61 with 0.80 limit) and CO (9.22 with 15.00
limit) were ok. My question is, if I were to replace the catalytic
converter do you think it would pass ? I have read that it also could
be the O2 sensor or EGR valve. Since the CO was ok and the check engine
light does not illuminate, I would think that the O2 sensor is ok. It
doesn’t look like this engine has an EGR valve. Has anybody had a
similar experience ? Any help would be appreciated

 

You're 100% right about the O2 sensor - that affects only the CO and will
light the "check engine" light if it fails. I believe you do have an EGR
valve - you need somebody more knowledgable in that area than I am.

Mike

 

nox is caused by excess combustion temperature.

if it's automatic, it will have an egr valve, but not if it's a stick.
if no egr, check the ignition timing. even a couple of degrees too
advanced makes a difference. you need to short the timing adjust
connector when doing it. if you have egr, remove the main valve & clean
it up. the soot buildup comes off with a wooden scraper - try not to
use metal scrapers on the main orifice or plunger if you can avoid it.
also, change the thermostat for good luck [taking care to use distilled
water when diluting the lost antifreeze] and check the valve lash.

if none of the above work, it's a new catalyst for you!