I have an 98 Civic Ex (1.6L Vtech, SOHC, 16Y8). It has 200'000 miles, but the engine is in great shape (no oil burning, no leaks, etc).
2 years ago it failed the smog check pretty bad. I ended up replacing both O2 sensors and the Cat. That was about 30'000 miles ago. Now it failed again. My numbers are as follows: %CO2: 14.5, %O2: 0, HC: very high (about double the allowable max), CO: high (about a third more than allowable), NO: very low (about a third less than average).
Anybody has an idea what could be wrong? Tune ups done regularly.
Thanks for the help in advance.

 

Just my .02 but in order to find out exactly what is causing your high Hydro carbons, you need to perform a complete diagnostic. From what I have heard, a high HC reading can be caused by running to rich or not adequatly burning the right amount of fuel.

If you want you can replace Plugs/cap/rotor/O2/wires/cat in that order.

Bump for someone who has more excperience.

 

Any CEL codes?

High fuel pressure?

Ignition/mechanical timing out of spec?

Thermostat stuck open?

 

Thanks for the suggestions.
No error code of any type, no problems. Timing is on the dot and thermostat works perfectly.
What I'm gonna do for now is I'll send in the fuel injectors for sonic cleaning and I'll put on a new fuel pressure regulator.
Any other ideas welcome

 

I would say do a full tune up also. And make sure you have changed your PCV valve. Besides that i wish u good luck.

 

More ideas:

Measure the fuel pressure before replacing the FPR.

Check whether any fuel injectors are stuck open before cleaning them.

Check for an exhaust leak near or upstream of the primary O2 sensor.

Test the primary O2 sensor.

Adjust the valve clearance to spec.

 

Thanks, I didn't think of the PCV valve. Completely forgot about that one.

 

Check your exhaust manifold for cracks between the runners.. It is a known problem.

 

I'm pretty sure none of the injectors are stuck open, but some may be clogged up to a certain degree. I'll get a report on the injectors. Flow-rate before and after cleaning, resistance, etc.
I had it done with the injectors on my 88 CRX Si just because it had 300'000 miles. 2 were fairly clogged up. Car runs much better now.
About the leak in the exhaust manifold. I'll check but I doubt it since I have a fairly new header on it.
Thanks to all for the help

 

engines just pollute more after long periods of time. try using some engine restore and fuel system cleaner