my car:
1998 Honda Civic Ex 243,XXX miles. check engine light is not on..
All aftermarket Parts are carb legal
OBX cat back
Aem short ram
Airmass Headers

What could be the problem??

p.s i don't have the print out so i don't know the exact numbers all i know is that they were too high..

 

heres some tips you might find useful.
http://www.smogtips.com/failed-high-...rous-oxide.cfm

 

carb legal doesn't mean they're smog legal, FYI.

When was your last tune up? Plugs, wires, rotor, cap, injector cleaner, timing belt?

 

CARB legal just means you won't get hassled for them in CA. Doesn't mean they have anything to do with you passing smog. 243k miles sounds like a pretty tired engine to me.

 

nox is usually due to a catalytic convertor going bad.

 

Thanks for the help everyone now to find the exact cause.

 

1. Get a new OEM Cat converter for around 300-500 dollar. A use one will be fine but make sure its not damage and know for sure it will pass smog
2. Before you do smog, put in new cat
3. Take it to smog station and smog it
4. After you pass, put back on old Cat converter
5. Repeat from STEP 2 every time you need to do smog

 

That is quite possibly the most pointless waste of money I've ever seen. You can get a Magnaflow cat with the right size piping and have it welded in by an exhaust shop for a hell of a lot less than $300. They also have good flow, so you don't need to do the convoluted mess of swapping it just to pass smog, which is technically illegal.

 

Catalytic converters are expensive in california.
Before you can just buy them for around 50 dollars on ebay and have them ship it here to cali. With the new laws that have recently passed, you can no longer do that.

New catalytic converters ranges from 150-300 dollars here now.

 

Awesome, another reason to add to the list of things to tell my recruiter the next time he asks me why I don't want to be stationed in "beautiful California". I feel sorry for you guys sometimes.

 

instead of paying for a new cat just pay to get your car smogged under the table, hassle free & cheaper if you find the right guy

 

Sounds like:

4. High Engine Mileage - Over an engine's lifetime, carbon build-up develops in the engine's combustion chambers. The more miles on your engine, the more carbon build-up on the pistons, cylinder heads and valves. Carbon build-up decreases the available space for the air/fuel mixture to combust, and causes higher cylinder compression. High compression results in high temperatures and high NOx. Keep in mind this problem is usually seen in vehicles with over 150,000 miles which have been poorly maintained. The solution to this problem is called De-Carbonizing. It usually costs around two labor hours at a smog check repair station. It will remove a good amount of carbon out of an engine. This will increase combustion space, lower compression and lower NOx.


Probably would do you good to do a 'Seafoam Treatment', just look it up on YouTube or Google, there are some good step-by-steps out there.

 

My civic did the same. The NOx at 25mph passed but failed at 15mph. My NOx read 1376 and I only replaced the cat. Took it the next day to get smogged and it read 0. Yes Zero! Mechanic told me cats from the dealer last around eight years but are hella expensive. Vs the universal/shop cats are good for a few years. So if you haven't changed it in at least two years and have a similar situation its 99% your cat.

 

yup, got my o2 sensor and cat changed and passed! 0! all oem honda parts. 310 for the dumb cat and 100 something for the dumb o2 sensor. pissed me off, but got it done.

 

I had a similar problem but not sure if its the same answer as yours. Mine read high on the 15mph (1047 PPM) and 25mph (0972 PPM). It's a D15B7 Engine. The Cat is oem honda maybe 2 years old. The O2 sensor is a year old. Just replaced air filter (Toyoroki D16z6 Air Intake), spark plugs (NGK Properly Gapped), Oil, Oil Filter, and ran GTB "Guaranteed To Pass" through it. MSD Ignition Wires as well. Run 91 Octane always and the timing is right. The motor is at 213k, but was rebuilt at 168k. I have a slight head gasket leak that I soon will fix. Valves need adjusting so to speak. New Distributor and Rotor. I did just install a new thermostat not too long ago that had a higher temp than the previous one. (180 rather than 174) Possible cause maybe cause the spark plugs show an indication of being too hot. Radiator is good and always filled same with reservoir tank. All hoses are good. No vaccume leaks. Idk what the cause is. Help???? Please!!!! Lol. Thanks!