[TestDrive]

Originally Posted by ConnClark

Okay,

I was wrong on one part. Its not grams per HP its grams per mile. http://www.epa.gov/otaq/cert/veh-cert/b00001a.pdf

It sure as hell isn't parts per million.

The pdf chart you're citing can be found at Federal and California Exhaust and Evaporative Emission Standards for Light-Duty Vehicles and Light-Duty Trucks | Cars and Light Trucks | US EPA where it clearly states -

The following tables of exhaust emission standards attempt to consolidate federal and California standards and implementation rates to facilitate comparison and to provide a one-stop resource for these emission standards. However, these tables are not a substitute for the official federal or California regulatory text. In addition, these tables do not reflect some emission standards, such as the federal cold temperature carbon monoxide standards and test procedures, or some optional standards that might apply to some manufacturers (e.g., small volume manufacturers). Each of the tables is potentially confusing without the accompanying Footnotes, Abbreviations and Definitions (PDF) document to help you sort things out (e.g., California calls cars "passenger cars" while EPA calls cars "light-duty vehicles").

The vehicle in question (a '93 Civic DX) is Tier 0 LDV (meaning a passenger car manufactured 1981 - 1993) and the very first line of data in the table applies. Since the car is over 10 years old, by federal standards it's exempt. But I assume Texas is expecting it to pass the 5 years / 50,000 miles standard.

In any case, footnote 39 of Footnotes, Abbreviations and Definitions (PDF) applies to both THC (Total HydroCarbons) and CO (Carbon Monoxide)

39. CERTIFICATION SHORT TEST (CST)

EMISSIONS FROM GASOLINE VEHICLES SHALL NOT EXCEED 100 PPM HC OR 0.50 PERCENT EXHAUST GAS CO AT IDLE AND 2500 RPM AT 4K MILES; COMPLIANCE STATEMENT ALLOWED (IN LIEU OF DATA)

Certification Short Test (CST) is also known as the Two Speed Idle (TSI) test. Which ever name you want to call it by, it measures HydroCarbons (HC) in parts per million (PPM). Read this Texas Department of Public Safety page Texas Emissions Testing Procedures and near the bottom you'll find.

What type of emissions test will my vehicle need?

El Paso, Travis & Williamson County Motorists
In conjunction with the annual safety inspection all gasoline powered vehicles from 2 through 24 years old which are registered or primarily operated in these emissions counties will be subject to one of the following emissions test.
1995 and older vehicles will receive the Two Speed Idle (TSI) test while 1996 and newer vehicles receive the On-Board Diagnostic(OBDII) test.

DFW and Houston/Galveston Area Motorists
In conjunction with the annual safety inspection all gasoline powered vehicles from 2 through 24 years old which are registered or primarily operated in these emissions counties will be subject to one of the following emissions test. 1995 and older vehicles will receive the Acceleration Simulation Mode (ASM) test while 1996 and newer vehicles receive the On-Board Diagnostic (OBDII) test.

If the car lives in El Paso, Travis or Williamson county, it was subjected to a TSI test. If it lives in the Dallas, Fort Worth or Galveston area, it was subjected to the more stringent ASM test.

If the TSI test was used, Hydrocarbons were measured in PPM. And if it was the ASM test?

Read this MOTOR MAGAZINE article -
http://www.motor.com/magazine/pdfs/051999_01.pdf
titled ASM testing getting a passing grade. If you're in a hurry, look at the table on page 3 of the pdf.

Originally Posted by ConnClark

As I stated before any leak in your exhaust skews the results in your favor.

Any leak? By a measurable amount? Do you have test data or can you cite a source to backup this supposition?

As I stated before: The exhaust system operates under positive pressure - above ambient atmosphere. If there is a hole, exhaust spews out the hole. Unless air enters the hole at the same time exhaust is spewing out (unlikely if the hole is tiny - quite possible if the hole is 1/8" x 1.5"), the emission ratios will not be affected. So far as I know, no testing equipment measures grams per mile directly. Grams per mile is always a calculated result based on a number of parameters. And some sort of emissions ratio always one of the required parameters in the calculation. An emissions ratio is the second to last step in each of the methodologies illustrated in this diagram - http://www.epa.gov/nvfel/methods/chemstry.jpg