Position of O2 sensor?

[K85 Octane]

I'm starting to question the position of my O2 sensor. I'm wondering if it's affecting how it reads.

When I built my exhaust I used some Edelbrock shorty headers but capped off the O2 bung. I welded a new bung closer to the Y pipe collector.

The sensor is a self headed unit, but does it still need to be installed in the header to work properly? Or maybe I'm getting a funky reading for my EFI because it's only reading one bank? Or is it being affected by scavenge from the other bank?

Just thinking about repositioning this, but is it worth it?





And the collector bolts up to the end of the exhaust, near the oil cooler lines. I can't see this being too far away but I really know nothing.

 

[4X4HIGH]

Well since you don't show a pic of where the sensor is now located I can only say that an 02 sensor must NEVER be mounted at or near the bottom of a tube but rather the best spot being the top side of the tube or on the side. Also the further the 02 sensor gets away from the hottest part of the exhaust the better the chance of the system never going into closed loop as the sensor MUST reach 600* in order to go closed loop operation. I findd it best to install a heated 02 sensor anytime you move it from the factory location.

 

[dyeager535]

There is some concern with latency and heat, but GM had many of these setups go open loop at idle anyway, so in those cases O2 sensor placement wouldn't matter, in terms of temp. Even with an unheated O2 and the sensor ~3ft from the closest exhaust port, mine would go closed loop at idle with the tiniest bit of throttle. (note that this is for the narrowband O2 sensors most of us run, not the wideband O2's that can accurately measure AFR well outside of only 14.7:1, where narrowbands are accurate)

Since this is heated, you eliminate that problem. IMO without tuning the PROM, the closer to the collector you are, the better. There is a delay factored into the O2 reading in many of GM's early setups, so the further back it is from stock, the more of a "lag" there will be in between what the O2 sensor sees and the amount of air/fuel changed going into the cylinder.

Look at it this way though: the O2 sensor is used at idle and cruise for a good mixture under those conditions. It has no bearing on WOT performance/power, so you being able to tell a difference based on where the O2 sensor is located, is unlikely.

I went from an unheated to heated O2 sensor, then changed the "lag" factor in the PROM, and noticed no difference in how it runs, or economy.

 

[Blue85]

If I'm guessing correctly about your setup based on the pics, you have a single exhaust down the driver's side, with the Y-collector sitting kind of next to the transmission. You put the bung just before the left and right streams come together. But are you measuring the left bank or right? The distance to the left is much shorter because you must have some kind of crossover pipe to the right. How far behind the header collector is this? What kind of "funky" readings or strange symptoms are you getting?

Measuring only 1 bank is OK. Generally putting the sensor in 1 header collector works better then moving it back behind where the two merge, because of the heat and distance. If you just capped the stock header bung, take the plug back out and put the sensor up there to try. You also need to be sure there are no exhaust leaks because that can really mess up the O2 reading.