Finally got my smog check done today. Passed everything, however, something caught my eyes.

The CO and NO were both well below the max allowed. However my HC at 15mph was at the max allowed. Max allowed HC at 15mph is 55, average is 9 and my measured was 55. At 25mph it was much better, max allowed is 39, average is 7 and my measured was 23.

What can cause my HC to be high?

Car is 2000 model with 43K miles. No engine or exhaust modifications.

Suggests welcome, comments...

 

I think the same thing happened with my car the last time I smogged it. Everything was way below max except HC, which was right near the max. HC's come from unburned gas. The cat is supposed to turn the hydrocarbons into CO2 and water. Maybe you're running a little on the rich side, or the cat isn't completely doing the job?

 

I made sure the car was nice and hot coming off the freeway but I had to wait about 30min before the actual testing began. When I got the car back the oil temp was below 200F so it wasn't fully warm. I hope it's not my cats, I have 4 of them and they are $$$$$.

Not sure why the car would run rich unless it went into warmup mode. But that's only suppose to happen on the first cold start of the day and for the first 10mins.


Might be time for another dyno run to get my O2 level checked :rick:

 

:rofl:

You could do that, or you could check your plugs and see if they are dark and smell like fuel.

 

yeah, plugs are a good place to start.
Check the oxygen sensor/sensors too.

 

Yeah I'm going to check the plugs. After 4 or so years of autox, I'm sure it wouldn't hurt to replace them :happysad:

 

they should be fine, I'm not getting a CEL and the car only has 43K miles.

 

i passed smog w/a broken cat and broken o2 sensor

 

4 cats? Dang.

Are they in parallel or series?

 

well i have headers with cylinders 1-3 exiting through the first one and 4-6 exiting through the 2nd one. each have 2 cats in series, I guess the first one is a precat technically.