98 Vette Failing HC ppm by 1 point?

[africke]

I'm new to tuning and the forum but I would like to say thank you for all the resources made available by this community.

I've been waiting to start using my hp tuner with my car for awhile and a week ago was motivated by my failed ontario emissions test.

It was passed last year with the stock exhaust and at the beginning of this year I installed 1 3/4 long tube headers, x pipe and borlas.

Everything passed except HC's, now I have only run 2 tanks of gas through her this year and this last (2nd tank) has been sitting for almost 2 months.

Latest Emissions test OCT 2010
HP ppm (limit 58) (reading 59)
C0% (limit.32) (reading .22)
NO ppm (limit 435) (reading 346)
RPM 1402
Dilution 14.8

I installed my wide band sensor and set it up with hp tuners and did a few logs etc.

I think HC means unburned fuel. Is there any way to lean the car out slightly without causing damage.

I'm sure you need more info and I can get you that if needed. A little direction may help based on the upgraded headers, x pipe.

I'm not looking to do anything illegal, I think by correcting the HC's it would be good for the car as well.

my test with the stock exhaust in 2009 ran these numbers
HP ppm (limit 58) (reading 22)
C0% (limit.32) (reading .06)
NO ppm (limit 435) (reading 152)
RPM 1404
Dilution 14.2

Thank you guys for any input you can offer.

Allen

[fasthotrod]

Glad to see you asking about how to make your car cleaner vs. trying to 'beat' the emissions. Talk about 'beating' emissions testing is taboo... and probably illegal.

That being said, educating yourself on the chemistry of the combustion cycle is the best way to understand that changes you can make to help your car run cleaner, and be better for our environment.

Here is a good write-up regarding the chemistry behind the combustion. (This is also some good info.)

As you can see in the articles, high levels of hydrocarbons (HC) are simply unburned fuel. There are a lot of different reasons why your hydrocarbon levels may be off the mark.

It's possible that your engine has a higher level of hydrocarbon emissions due to deposits in the combustion chamber. Cleaning the cylinders/heads with a chemical (Seafoam for example) may help bring your numbers within specifications. Maybe there is a fuel injector that is 'dribbling' and putting more fuel into one of the cylinders? Hard to know without testing it first-hand.

If your tune was off and your car was running more rich than ideal, then it would also explain the unburned hydrocarbons. I don't know what the chemical make-up of your fuel happens to be, but it's possible that your stoich value in your tune is off, or the actual stoich of the fuel differs from what the tune expects to see.

Be careful of leaning out your tune too much. While a tune with a a slightly more lean condition will be better to reduce the hydrocarbon levels, too lean of a condition can cause an increase in Nitrogen (NOx) emissions and/or cause cylinder temperatures that can damage your engine under load.

As always, responsible tuning that is in-line with your country/state/local laws is always encouraged, and is better for the environment. (As well as the public's attitude towards us.) Good luck.

[flame]

So its only failing the dyno portion and passes idle? How old are the O2 sensors?

[Nick 2K2 SS]

HC is unburned fuel. If you are not seeing any knock retard you might be able to increase your timing by a couple of degrees to give the cylinder a few more degrees of burn time and that might lower your HC's. Otherwise you may have to lean it out a little. It would probably be best to get a Wide Band O2 sensor so you can see if your mods have cause the car to run too rich as well. If it is running rich then that's good info so you can lean it out a little and that might solve your HC issue.

[africke]

Thank you very much for the info guys and taking the time to explain a few things! using that I was able to clean up my tune and was able to pass with satisfying numbers this morning.
I did adjust the timing a few degrees and it made a world of difference. Amazing how much all those gases affect each other.
Was able to run offline and fine tune a few things thanks to my mechanic being curious.
No power loss that I can feel, all my numbers still look good.

Thanks
Allen