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Kevfra · 06-29-2008, 01:24 PM

My headers have four bungs, so all four are plugged in.

So you say the first set adjust the mixture - makes sense. And the second set tests for cat performance...then what? Seeing the cats not perform well does it adjust the mix or simply throw a code? I would thik it does not make any correction in the burn, leaving this to the first O2 sensors.

I have not thrown a code and obviously my cats are not performing. Many others have done this and also not thrown a code. Perhaps the failure mode for the cats does not include a burn like mine, but rather some other mode of failure the system is looking for?

My engine is running warmer - slightly. And while it may be this is due to a lean mixture I have another thought...where is the temperature sending unit located? I suspect it is near one of the headers and is getting local influence from the heat of the header pipe, giving it a reading different than the actual coolant temperature. I have a laser temperature guage and could read my coolant directly, but since I didn't do that beforehand I wouldn't have any comparison to go by. If indeed the temp sender is near the header I can do a quickndirty shield to test my idea.

06-29-2008, 01:24 PM	#72
Kevfra Registered User Join Date: Mar 2008 Location: San Francisco Posts: 66	2nd set of O2s My headers have four bungs, so all four are plugged in. So you say the first set adjust the mixture - makes sense. And the second set tests for cat performance...then what? Seeing the cats not perform well does it adjust the mix or simply throw a code? I would thik it does not make any correction in the burn, leaving this to the first O2 sensors. I have not thrown a code and obviously my cats are not performing. Many others have done this and also not thrown a code. Perhaps the failure mode for the cats does not include a burn like mine, but rather some other mode of failure the system is looking for? My engine is running warmer - slightly. And while it may be this is due to a lean mixture I have another thought...where is the temperature sending unit located? I suspect it is near one of the headers and is getting local influence from the heat of the header pipe, giving it a reading different than the actual coolant temperature. I have a laser temperature guage and could read my coolant directly, but since I didn't do that beforehand I wouldn't have any comparison to go by. If indeed the temp sender is near the header I can do a quickndirty shield to test my idea.