Cobb Stage 2 and Rear o2 - Page 2

ParkerSTi · 05-11-2005, 01:26 PM

rodent:

My understanding is this: The ECM makes decisions for the A/F based on input from the front O2 sensor and the rear O2 sensor. The front does most of the input with the rear doing the fine adjustments. The ECM based on what it sees from these two sensors (and other I/O) is constantly adjusting the A/F based on the stored map(s).

You might be able to get away with disconnecting the rear O2 sensor, but if you have a cat I would keep the rear sensor hooked up to keep from long term degradation of the catalyst element. It can scorch if too lean or explode if overly rich condensation is allowed.

rodent · 05-11-2005, 01:59 PM

I don't have a cat.

I talked to Cobb and they said it shoudn't hurt anything by having it out. They said I could short the two heating wires together but don't suggest it. I think I'll just get another o2 bung welded in and re-install it.

ParkerSTi · 05-11-2005, 02:11 PM

rodent:

Hate to say it, but that might be your best option.

And for shorting the heater wires, I think that could cause problems since they are sourced from the ECM.

My TBE came with an extra bung just below the turbo for just this sort of application, but I have never used it.

ValvetrainEngineer · 05-11-2005, 05:40 PM

Yes, the first O2 is used for engine control, the rear is solely used for OBD II (emissions) monitoring...

STirish · 05-11-2005, 06:51 PM

I think the '05s only have one O2 sensor, you guys were really worrying me for a second

RXAK · 06-24-2008, 03:08 PM

Thread back from the dead.

I just installed on my 05 STi a Greddy Evo 2 mid and cat pipe with an Invidia V2 DP.

The O2 Sensor won't fit in the supplied bung so I just plugged the hole and disconnected the sensor (the sensor bumps against the drive train). How do I get rid of the CEL for the o2 sensor? My Cobb AP resets it temporarily until I turn the car off. Then it reappears.

I searched this site for some kind of fix, but can't seem to find a definitive answer.

Can anyone help on this?

Thanks

05-11-2005, 01:26 PM	#16
ParkerSTi Professional STI Driver Car: Subaru Fav Mod: N/A Location: N/A Posts: 436 Join Date: Oct 2004 Trader Rating: (0)	rodent: My understanding is this: The ECM makes decisions for the A/F based on input from the front O2 sensor and the rear O2 sensor. The front does most of the input with the rear doing the fine adjustments. The ECM based on what it sees from these two sensors (and other I/O) is constantly adjusting the A/F based on the stored map(s). You might be able to get away with disconnecting the rear O2 sensor, but if you have a cat I would keep the rear sensor hooked up to keep from long term degradation of the catalyst element. It can scorch if too lean or explode if overly rich condensation is allowed. This ad is not endorsed by this member. Please register or login to hide this ad.

06-24-2008, 03:08 PM	#21
RXAK Amateur STI Driver Car: Black 05 WRX STi Fav Mod: Coming Soon Posts: 15 Join Date: May 2008 Trader Rating: (0)	Re: Cobb Stage 2 and Rear o2 Thread back from the dead. I just installed on my 05 STi a Greddy Evo 2 mid and cat pipe with an Invidia V2 DP. The O2 Sensor won't fit in the supplied bung so I just plugged the hole and disconnected the sensor (the sensor bumps against the drive train). How do I get rid of the CEL for the o2 sensor? My Cobb AP resets it temporarily until I turn the car off. Then it reappears. I searched this site for some kind of fix, but can't seem to find a definitive answer. Can anyone help on this? Thanks This ad is not endorsed by this member. Please register or login to hide this ad.

05-11-2005, 01:59 PM	#17
rodent Professional STI Racer Car: 95 GSX Location: Highlands Ranch, CO Posts: 810 Join Date: Mar 2004 Trader Rating: (4)	I don't have a cat. I talked to Cobb and they said it shoudn't hurt anything by having it out. They said I could short the two heating wires together but don't suggest it. I think I'll just get another o2 bung welded in and re-install it.

05-11-2005, 02:11 PM	#18
ParkerSTi Professional STI Driver Car: Subaru Fav Mod: N/A Location: N/A Posts: 436 Join Date: Oct 2004 Trader Rating: (0)	rodent: Hate to say it, but that might be your best option. And for shorting the heater wires, I think that could cause problems since they are sourced from the ECM. My TBE came with an extra bung just below the turbo for just this sort of application, but I have never used it.

05-11-2005, 05:40 PM	#19
ValvetrainEngineer Spec C Club Car: '04 WRB Fav Mod: A working ECU... Location: CT Posts: 1,486 Join Date: May 2003 Trader Rating: (7)	Yes, the first O2 is used for engine control, the rear is solely used for OBD II (emissions) monitoring...

05-11-2005, 06:51 PM	#20
STirish Spec C Club Car: '99 M3/'03 WRX Avant Fav Mod: Modification is wrong! Location: SLC, UT Posts: 1,026 Join Date: Sep 2004 Trader Rating: (6)	I think the '05s only have one O2 sensor, you guys were really worrying me for a second