I just failed Smog, only at 25MPH NO. Measured 1088, Max 798. I know nothing about cars, but thought it is time I started trying. Thanks!

Here are the full results of the failed test:




Here is my test from two years ago that passed:


1. I was told it could be the O2 sensor. Does that sound reasonable?

I just had the spark plugs & cap/rotor replaced.

2. Anything I can do to test or check this ahead of time?


Assuming it is the O2 sensor:
1.A local mechanic quoted me $200 out the door to replace the O2 sensor. Is that reasonable? He said he only uses honda oem parts.

2. There are two in my car, right? Do both need to be replaced?

3. Can I just do this myself? I could not find a video for my exact car, but similar civics seemed easy enough.

4. Compatible sensors on eBay are quite inexpensive--$16-$25. What O2 sensor would you use if it was your car?

 

Any mechanic will tell you they use OEM parts. When was the last time you had any maintenance done?

 

You have one o2 sensor, it's a heated sensor and is the upstream just at the bottom of the 4 to 1 header in the collector area right in front of the radiator.

You can but o2 sensors can be a real pain in the *** to get out. One trick I've come up with is to use a band strap on the o2 socket. The type of band strap with a hex/flat tip screw on it to tighten up. The o2 socket has a side cut open to allow the wires of the sensor to have a palce to go. The drawback is the end of the socket flexes and will round the nut portion of the o2 sensor. My trick is to put the band strap down over the wires first, then put the socket on, then position the band strap at the bottom of the socket and tighten it down tightly with the socket in place on the nut. Then you can use a breaker bar or impact wrench to get it out and the socket won't flex on the nut.

Heat is also your friend for stubborn nuts/bolts. A blow torch can allow you to get these PITA nuts and bolts off.

I personally bought a Denso o2 sensor for my CDM CX. I'm in Canada so parts tend to be more expensive and I was able to get the quality OEM part for 100 bucks from my local Honda/Acura specialist. Nippon Denso is one of the OEM brands for the o2 sensors. I believe there is more than one brand Honda has used on their cars.

 

I had a mechanic look at major services last week in preparation for smog. He did:
oil/filter, transmission oil, spark plugs, caps/rotor, air filter element, V/C gasket, grommets.

He looked at but did not do anything to: tires, brakes, fuel line, cooling, steering, suspension.

Prior to that was 10,000 miles ago (7 months ago). Head gasket, thermostat, timing belt, water pump, oil, and fluids.



TomCat39: I will look at Nippon Denso and see if his pricing seems fair. Thanks for giving me the location--I'll see if it seems like something I can get at with my general lack of tools.

This looks like the proper part from Denso?: http://tinyurl.com/Denso-O2-1992-CX-1-5L


Back to the smog question--does it seem reasonable to replace the oxygen sensor outright? Is there any way to test the oxygen sensor before spending the time or money?

 

The problem is NOT the O2 sensor, whoever told you that is not familiar with emissions sytems.

Was this an ASM or TSI test?

ASM = Mustang Dyno
TSI = No dyno


If ASM, you can bandaid this by gapping your spark plugs really low (like around 0.025") and retarding the timing all the way and it should pass, but the problem most likely lays in your catalytic converter although in some cases it could be internal issues like rings or exhaust valves.

 

The engine is running lean. Replace the fuel filter and then check the fuel pressure and FPR.

Also check the ignition timing as per the service manual.

 

I am at 11 BTDC right now, specs on the hood are 10 +/- 2, so I could get the mechanic to retard it to 8 to try to pass smog?

OK--will replace fuel filter and check fuel pressure and FPR.

Is this an adequate fuel filter? Is there a manufacturer I should use instead?
GF54689 G6826 Fuel Filter Fits Honda Accord Civic Del Sol | eBay



Ahh, yes this had a treadmill (dyno?) so that should mean it is ASM, right?

 

That's fine.

Should be fine.

 

@ RonJ

CO measured at 0.01/0.02

Excess lean condition causing NOx this high would bring CO above 0.50%.


Tuning out by adding fuel is just a band aid for the real problem of which we do not know unless the OP tests for it.

 

Also, my car fails to start if I start it, run for a short time, then turn it off and attempt to start again within 30 seconds. Waiting 3-5 minutes and I can start it normally.

Does that help at all?

I will order that fuel filter. Strike that, ordered. Will arrive in 2-3 days.

Googling how to test the fuel pressure.

 

On a theoretical basis, given the very low HC levels, I'm not surprised by the very low CO. Seems to be a classic case of running too lean.

 

Could also be clogged fuel injectors, but start with the fuel filter and fuel pressure.

 

Gracias!

edit: finally replaced fuel filter and also replaced oxygen sensor as I only had a few days left until I needed to pass smog. Pressure was fine, so FPR should not need to be replaced (right?)

I barely passed with ~791 NO (fail is 799), the measured HC went up quit a bit as well with 49/30 at 15 and 25MPH respectively, but still well within passing range.

It looks like something else must still be wrong, so if anyone has any additional suggestions I can try something else so that I am not in this position again in two years.


If it matters, my mileage has been fine both before and after these changes. I average ~39MPG freeway with 41.5 two tanks ago!

Thanks for everyone's help!