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I installed bbk long tube headers with high flowing cats and I cant seem to pass Illinois state emissions! My mechanic cant seem to figure out why because when he connects his machine it doesn't give him any codes and my check engine light doesn't come on. Does anyone know what it could be or if there is a fix? I cant be the only one in the entire state of Illinois with longtube headers
 

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I mean, how about a little more information on your car?
 

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Discussion Starter #3
Sorry, first time ever posting on a forum. I have bbk 1 7/8 long tube headers, high flowing cats, borla s-type, 4:10 gears and a bama tune
 

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The tune is worthless, however, don't be surprised if the cats are at least partly to blame.....Good luck..
 

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The down stream O2 sensor readings are used by the ECU to measure how well the cats are working by comparing to the upstream O2 sensors. High flow cats quite often won't pass the check the ECU makes and will cause a check engine light. Tuners know this so they turn off the down stream O2 sensors. This will prevent a code and check engine light. But, there is another parameter that the inspection station looks at cslled status monitors, if these are not ready you will fail emissions. I would expect that the O2 status monitor is not ready because it is not getting a signal from the down stream O2s.

Not sure what equipment your mechanic has but even relatively inexpensive OBDII readers can look at the status monitors. If his can't find someone that has one that does to verify if it is the status monitors.

If it is, you will need a tune that does not turn off the down stream O2 sensors then you will need to get O2 extenders that move the O2 way from the direct exhaust flow. This will trick the ECU into thinking the high flow cats are working in spec.

Note: the reason for the status monitors is to keep people from clearing codes before going in for inspection and get a pass before the code comes back. They do this by taking a 100 miles or more and a number of start cycles after the ECU has been reset to clear codes or load a new tune.



Dave
 

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The reason they have for "For Offroad Use Only" right on the box.
 
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Both of my GT500's needed Kooks " green " cats to pass inspection with LT's, high flow cats threw codes..
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