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Old 07-01-2005, 06:42 PM   #1
Scooby Newbie
Member#: 71361
Join Date: Sep 2004
Chapter/Region: BAIC
Location: SFBay
2000 Impreza 2.5RS

Lightbulb Emissions and hi-flow cat converters

Being new to OBDII and California, I had a couple questions which the Random Tech(RT) guys were so kind enough to answer, so I thought I'd share:

Me: Kinda of new to all of this, so trying to understand... if aftermarket hi-flow cats work just as well at meeting emissions standards, why are they technically illegal? Googling around, I found "as of early 2005, only a few 1997 and later OBD II catalytic converters have been granted an exemption".

Go easy on me if this is a dumb question, but what's their dealio?

Not a dumb question at all. CARB has made the exemption process for OBD2 converters very complex and expansive. For OBD1 applications, it is possible to go through a "worst case" test-- heaviest vehicle, biggest engine-- and the EO applies to all vehicles that are lighter in weight and/or have a smaller engine. the cost to go through this testing is $50,000 to $70,000. For OBD2 applications, converters must be tested for each engine family. As a result, total costs will be significantly higher if a company wants broad market coverage. A few companies have been granted exemptions for pickup truck applications, but there's little else available in California-legal OBD2 converters.

The problem for car owners is that the CARB position makes converter replacement unnecessarily expensive, because only original equipment replacement converters are legal. None of this has anything to do with tailpipe emissions-- it's all a paperwork issue. We've heard of may California drivers whose cars passed the tailpipe test with flying colors, yet failed the visual inspection because they had installed an aftermarket converter. EPA takes a different approach and allows the installation of aftermarket converters on OBD2 vehicles. EPAs concern is that the vehicles are emissions compliant, not whether or not the vehicle is equipped with an "approved" catalytic converter.
Me: A lot of people with obdII cars get a MIL from the high flow cats (0420 - cat below efficiency) and put an eliminator spliced into the rear o2 sensor to stop this. Since the code is thrown from the ecu because the resistor temp reading is lower than it would be for a reg cat, I was considering putting a different resistor inline instead of and eliminator....... thus the question: what is the nominal operating temp for one of your high flow cats?

Actually, 0420 codes are not set because of temperature. While it is true that if a converter cools off too much, there will be a significant decrease in conversion efficiency, the most common cause of 0420 codes with high flow converters is that the exhaust passes through the converter too quickly. As part of the catalytic process, converters cause free oxygen to for various oxide compounds. With a stock converter, the exhaust spends a lot more time inside the converter because it's relatively restrictive. The greater the length of time the exhaust spends inside the converter, the more time there is to form oxide compounds, and vice versa. The oxygen to oxide conversions are part of the same process that converts carbon monoxide and unburned hydrocarbons to carbon dioxide and water. Oxygen sensors are cheap and reliable, so that's the sensor of choice for monitoring converter efficiency. The assumption is that if a converter is operating at proper efficiency, it's going to converter virtually all free oxygen into some form of oxide. That assumption is only partially true. We've seen a number a vehicles pass tailpipe sniff tests, even though the ECM had set a 0420 code and turned on the MIL.

The short answer to your question is that internal temperatures in virtually all converters ranges between 600 at "light off" to 1200 degrees F during normal operation.
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Old 07-02-2005, 09:24 PM   #2
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Join Date: May 2005
Chapter/Region: BAIC
Location: Monterey Bay Area
2002 Impreza WRX


so basically the RT pipes a smog legal, but visually illegal in Cali? whats the best way around this problem? or is there no way around it?
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