Emission Q - High HC count

[InvalidUserID]

Hi all,

I just got my 2008 CA registration notice and saw that I have to take my 1996 V6 Camaro to a "gold shield-test only" station and I'm a little nervous due to my last test barely passing the HC test. The following is my last test results.
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Chevrolet Camaro, 160,520 miles
7/30/2006

15MPH test (1544 RPM):
%CO2 - 13.6
%02 - 1.7
HC (PPM) - 51 measured (51 max allowed)
CO % - 0.13 measured (0.49 max allowed)
NO (PPM) - 266 measured (424 max allowed)

25MPH test (1537 RPM):
%CO2 - 13.2
%O2 - 2.1
HC (PPM) - 15 measured (36 max allowed)
CO % - 0.03 measured (0.46 max allowed)
NO (PPM) - 33 measured (711 max allowed)
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When that test was performed, it was still the factory cat as well as some pretty old plugs (at least 3 years old/60k). Since that time, I've replaced the two manifold o2s and replaced the factory cat. This weekend, I'm going to replace the spark plugs, wires, fuel filter and clean out my cold-air intake filters. I've also installed CARB headers, but that shouldn't factor into anything. My latest UOA showed no fuel, coolant or water in the oil and the car hasn't set a CEL in a while.

With this latest PM, the HC count should come down, shouldn't it? I don't know, maybe that 51 out of a 52 allowed just got me a little scared.

 

[artificialist]

It ought to pass.

Another thing I'd look at is see if the thermostat is opening too early. If it does, the lower engine temperature will cause combustion to become less efficient.

I'd also run some seafoam through the vacuum lines to blow out junk that stuck to the intake manifold, cause unequal air distribution, and therfore a cylinder running richer than other cylinders.

 

[tom slick]

you should be ok.

 

[Rhymingmechanic]

To go along with artificialist's comment about the thermostat--If you're close to the station, be sure to take a long drive to get the engine and cat hot. My HC results for a '94 Saturn dropped significantly by doing that. (Changing the stuck-open thermostat before the second test probably helped, too.) The station was 5-10 minutes away, with both tests in fairly cool weather.

2004
2500 RPM--125
idle--144

2006
2500 RPM--23
idle--55

(HC limits for both RPM were 220)

Good luck.

 

[InvalidUserID]

Originally Posted By: Rhymingmechanic
To go along with artificialist's comment about the thermostat--If you're close to the station, be sure to take a long drive to get the engine and cat hot. My HC results for a '94 Saturn dropped significantly by doing that. (Changing the stuck-open thermostat before the second test probably helped, too.) The station was 5-10 minutes away, with both tests in fairly cool weather.

2004
2500 RPM--125
idle--144

2006
2500 RPM--23
idle--55

(HC limits for both RPM were 220)

Good luck.


The shop I took it to back in 2006 was only about a 7 minute, 5 mile trip down the freeway although they did a pre-test before the real smog, so that probably warmed it up a bit too. I plan on taking it to a shop closer to my work which would be closer to 25 miles on the freeway to give it a chance to full warm up, as well as a pre-test again.

 

[TooManyWheels]

Check out the following link for some more ideas on the high HC

Using a 5-Gas Analyzer

This is a great site to bookmark for troubleshooting emissions problems.