Deleting sensors

[DMC7492]

Hi guys I am in the middle of the wiring experience. Based on the tuners what is needed to tune properly? Do I need the following?

Rear O2
EGT

currently my EGT has a 14 K resister in the connector.

Thanks Guys for the help!! Don

[Bob_n_Cincy]

Hi Don
Turn In Concepts wanted my Rear O2 installed.
My EGT was already installed so they did not comment on that.
Bob

[DMC7492]

Is the rear o2 the only one used? in this position. For a street driven car?
And also is the front totally eliminated?
Stock O2 or wide band?
41702

[Pearldrummer7]

I don't have my EGT installed. I've heard horror stories of them shearing off and going up into the turbo (at least the 2002 ones mounted in the uppipe). I don't know if that's likely, but no reason to risk it. I'd like to monitor EGT from elsewhere (right behind turbo in the "downpipe", perhaps).

[STiPWRD]

Don, I believe the rear O2 is mainly used by the ECU to adjust long term fuel trim. If you can try to keep the rear O2, it's probably for the best. I drove my wrx for years with a wideband O2 in place of the rear O2 and didn't have issues. I did however plug in some resistors into the rear O2 harness connector to fool the ECU into thinking there was still a narrowband O2 sensor there. This got me through emissions. The front O2 is essential and regulates short term fuel trim. I also removed my EGT sensor, plugged the up-pipe with a bolt and connected a resistor to the connector. This also did not cause any issues. I think the EGT is mainly used to monitor pre-cat temperatures related to emissions control. If you do plan on running an EGT sensor, I've heard the best place to mount it is as close to the engine exhaust ports as possible coming off the hottest cylinder (1 or 3 as they are close to the up-pipe/turbo). I would highly suggest getting a wideband.

[Buzz Skyline]

I thought the rear O2 was almost exclusively for emissions to make sure the cat is working. I think the forward O2 is the critical one for tuning. As I recall, the EGT was handy when tuning with the open source tuning program I used on my Evo, but I believe that it doesn't give you much more than confirmation of other things that can affect temperatures (like air fuel ratio) and perhaps a warning that something is going very wrong.

[STiPWRD]

I thought the rear O2 was almost exclusively for emissions to make sure the cat is working.
That could be the case, I'm not certain. I just know that I ran without a rear O2 for years and it didn't cause issues for me.

[Buzz Skyline]

If it's only for emissions, it shouldn't cause any problems if you delete it, other than a check engine light. Even that you could probably get rid of with the right resistor across the contacts in the O2 connector.

[Bob_n_Cincy]

Here is what the 06 Subaru manual says.

http://thefactoryfiveforum.com/attachment.php?attachmentid=41728&d=1430932578

[Buzz Skyline]

Of course, the chemistry of the exhaust will be changed by the catalytic converter, so even though the manual implies that the second O2 sensor is important for tuning, it's really just for emissions, to ensure that the cat is working properly. The first O2 sensor is the only one that can give you useful info for tuning and performance (and for achieving stoichiometric conditions under the closed loop ECU operation). If you put in a wideband O2 sensor for tuning with the Tactrix system, for example, it has to go upstream of the cat for that reason. So you can delete the downstream sensor with no performance impact, I believe.

[Slatt]

I don't have my EGT installed. I've heard horror stories of them shearing off and going up into the turbo (at least the 2002 ones mounted in the uppipe). I don't know if that's likely, but no reason to risk it. I'd like to monitor EGT from elsewhere (right behind turbo in the "downpipe", perhaps).

I've heard the same stories. In my case I have one of those PSI3 ECU monitors and it shows EGT (along with many other ECU values, hey, it's a great toy to have on your dash). It's becoming obvious that the signal from the stock EGT fails long before it actually disintegrates into the turbo. I'm about to install my 4th EGT sensor in my 70k mile 03 WRX. I never get a CEL when the EGT fails. Which all kind'a makes me wonder just how important that sensor is.

[icky]

If you are removing the cat from the up pipe it is imperative that you remove the egt sensor, replace it with a plug and resistor. You need both o2 sensors for the oem ecu to do its thing.

[Buzz Skyline]

The values.the rear O2 sensor provides can't be part of the ecu tuning calculation. It can only report on the catalytic converter's operation, so yes the ecu uses it for emissions monitoring, but not for performance or air fuel ratio feedback. That requires info from upstream of the cat.

In fact, people often have to add an adapter to the rear O2 sensor after they have installed high flow cats. It fools the sensor into reporting better cat operation than they are actually getting. Tuning, however, is not affected by the adapter.

[DMC7492]

Okay guys tanks for the info. I discovered the front O2 is in the right manifold and the rear is going into the bell mouth or down pipe. My EGT is resistored with a 2.2K resistor. The up pipe is a Grimm Speed so there is no bung for the EGT. That is the part that threw me for a loop.
After looking at the wiring it is apparent the front sensor seems to be more shielded robust and the rear appears to be just a sensor. I will use both and I am sure the tuner will be looking at both feedbacks to tune properly.
See picture41763

[STiPWRD]

Does anyone see an issue with using a downstream O2 in place of an upstream O2? My upstream O2 sensor is old and I have a new downstream sensor so I was going to cut the connector off the old upstream, solder it to the new downstream O2 and bolt it into the upstream location. As far as I know, both upstream and downstream sensors use 4 wires (signal, ground, 12V+, heater) and have a 0-1V output signal. For some reason new upstream O2 sensors are much more expensive than new downstream sensors.