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Old 09-27-2005, 04:14 AM   #1
drdeuce
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Member#: 36075
Join Date: Apr 2003
Location: Calgary, Alberta, Canada
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2004 STi 2.65L GT35R
Hydra

Default Is there a reason the Front O2 sensor is before the turbo?

I know that most O2 sensors don't depend on where they are located.

But is there soemthing unique about the factory front "Wide-range" O2 sensor that requires it before the turbo?

My reason for asking is becuase my new setup was made just for a Hydra and the front O2 sensor bung has been welded shut. I'm now having issues with the Hydra and want to put the stock ECU in, but the only conveniet place I have for yjr O2 sensor now is in the Downpipe behind the turbo. Should there be a problem putting it here?

thanks
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Old 09-27-2005, 08:53 AM   #2
Wombat North
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Default

Jay,

FWIW
I have a spare bung if you want me to weld it on in the stock location. FOC

I could also redrill the hole and tap a new thread.

PM me if you want to go the above.
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Old 09-27-2005, 11:56 AM   #3
drdeuce
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Hydra

Default

Thanks, actqually the bung is still there and I could probablu get the plug out as it was just lightly welded, my My whole headers in wrapped in about an inch thick of exhaust wrap. I don't really wan to pull the header and revove the 8hours labout it took to do the wrap just to test the Stock ECU for a few minutes.

I'll just put it behind the turbo and see how it works.

Jay
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Old 09-27-2005, 02:32 PM   #4
MikeWRX-NJ
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i don't have an answer to your question but i do know the JDM twin scroll setup has the o2 sensor a few inches from the turbo in the downpipe.
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Old 09-27-2005, 05:12 PM   #5
drdeuce
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Thanks. Thats useful to know.
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Old 09-27-2005, 08:29 PM   #6
hatchy
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Just a guess, but O2 sensors work best only when they are at a properly temp range. Closer to the exhaust manifold == hotter so the ECU doesn't have to turn on the heater element in the sensor to get an accurate reading?
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Old 09-27-2005, 09:17 PM   #7
nhluhr
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You want the O2 as close to the cylinders as possible to ensure quick response time.
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Old 09-28-2005, 05:51 PM   #8
drdeuce
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Hydra

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OK,

To answer my own question, it appears that it works in the downpipe. It does seem like the AFR takes a bit longer to respond than usual, but it's not a huge problem.

This now seems to confirm that all the drivaility issues I was having were with the hydra. Defective unit is the likely cause, but I won't know for sure until I send it back to Element and Phil checks it in a car.

With regards to the sensor being as close to the combustion chambers as possible, it makes sense but many 02 sensors are not. Most aftermarket ECUs that run in closed loop (Hydra, AEM) for WOT tuning don't have the O2 Sensor after the turbo. Whether that matters, I don't know. I've also been advised by many (PDX) that if it is too close the the turbo the reading are innacurate. I think becuase of heat, but not sure.


thanks

Jay
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