Running a wideband gauge

**SeekB00st** · 04-12-2010 08:04 AM

Running an AEM wideband. Now as you know I have three oxygen sensors. What am I suppose to do with the third? Also, I installed the one before the cat - this is the correct way to run them right?

**Seerlah** · 04-12-2010 08:39 AM

The one before the cat (pre cat 02 sensor) is needed if you are using the stock ECU. Without that, your ECU will not be able to correct for proper A/F ratio. The post cat oxygen sensor (downstream sensor, after that cat converter) is not really needed and you can have that file written out. But if you don't have it written out, then you will throw a CEL for it. You will also need to close that bung with a plug. That 02 sensor is there to basically just monitor your exhaust flow (ie CEL codes related to the catalyctic converter are granted because of this sensor). Or just leave it plugged in.

To install the wideband 02 sensor, you will need to have a 3rd bung welded onto your existing dp/tp/hfc or whatever you have. Your wideband 02 sensor, should sit basically right next to your stock primary 02 sensor. Any exhaust shop should be able to handle that for you. And if they can't, then they should close shop.

http://vibrantperformance.com/catalo...f3d3d5710d19e6

**SeekB00st** · 04-12-2010 11:06 AM

I have the precat installed and the wideband. The post cat is just sitting.
So basically I'm straight. I can unconnect the harness for the post cat and just leave it sitting in my room correct?

**Seerlah** · 04-12-2010 11:35 AM

You can do that, but not sure if it is the proper way. You are supposed to have the wideband sensor as close to the exit of the exhaust housing of your turbocharger to get the most accurate reading. This is why the stock sensor is located right at the exit point of the turbocharger, so it can get the most accurate reading.

With you leaving the secondary 02 sensor unplgged, you WILL get a CEL for it unless you have it written out of your ECU. The way you are doing it will work, but isn't the correct way to do it. The bung you have the wideband plugged into is really supposed to be meant only for the secondary 02 sensor. For an aftermarket wideband sensor, such as your AEM, you are supposed to have an extra bung welded onto whatever you have coming from your exhaust housing (test pipe, stock cat, hfc, or dp) and attach your wideband sensor onto that.

That is why I left that link in my previous post. The proper way to have your car set up would be to place the secondary 02 sensor back into the bung it was meant for (if you don't want to use your secondary 02 sensor, you should have it written out of your ECU and plug that bung. plugs for the bung are also on the link I previously posted). Purchase a bung, such as the one in the link in my previous post, take your car to an exhausrt shop, and have them place that extra bung around the area of the primary stock Bosch 02 sensor. Then, place your AEM wideband sensor into that bung. As I mentioned, the way you have it will work. But it would have a more accurate reading if the sensor was right where your exhaust gases exist your engine (which would be right after your turbocharger).

**SeekB00st** · 04-12-2010 12:49 PM

Thanks for the valuable information.
Now mr tech help me out with this. I desire your knowledge.

http://www.audizine.com/forum/showth...ugs-wont-spark.

**nagle10** · 04-12-2010 03:03 PM

Your supposed to install the bung downstream from the turbo. If you put the wideband sensor too close to the turbo you will burn it out.

**Seerlah** · 04-12-2010 03:06 PM

^I thought that at first, but noticed that the 034 dp has the 3rd bung maybe 1-2" down from the primary 02 sensor. That is where I drew my conclusion from. Also, my primary 02 sensor is a wideband and is right where all the other 02 sensors are for the B5 A4 1.8t. Hopefully, someone can chimme in to confirm.

**SeekB00st** · 04-12-2010 03:45 PM

Yea that'd be nice. I have a full down pipe very similar to that.

**nagle10** · 04-12-2010 04:52 PM

They just put the second 02 sensor closer to the turbo to install it easier. There is no cat on that downpipe so it makes no difference were the 2nd o2 sensor is. The bung all the way down past the flexpipe is for the wideband.

**lowandslow4now** · 04-12-2010 05:01 PM

Originally Posted by Seerlah

^I thought that at first, but noticed that the 034 dp has the 3rd bung maybe 1-2" down from the primary 02 sensor. That is where I drew my conclusion from. Also, my primary 02 sensor is a wideband and is right where all the other 02 sensors are for the B5 A4 1.8t. Hopefully, someone can chimme in to confirm.

I have this kit. Literally this kit the first and second my primary and secondary O2 sensors and the one at the bottom of the downpipe is for my wideband. I have not had to change an O2 sensor yet. My AFR is right on.

**Seerlah** · 04-13-2010 02:19 AM

Thanks for correcting me

**.Mad Hatter.** · 06-11-2010 03:51 AM

so to clarify for future reference; the wideband bung should be after the flex pipe? any measurement used for reference, I have read at least 18" from the exhaust housing on the turbo???

**nagle10** · 06-11-2010 07:25 AM

It doesn't have to be past the flex pipe. I would say aslong as its past the tranny support bracket you are good.

**SeekB00st** · 06-11-2010 09:31 AM

The post above me is accurate. Also, you will need all of your 02 sensors plugged in

**.Mad Hatter.** · 06-11-2010 10:08 AM

yes i have gathered that. i see some guys using the second O2 bung, but they are still leaving them plugged in either way.

**97B518TQM** · 06-11-2010 10:47 AM

The wideband sensor needs to go after the HFC or Cat. I had mine there instead of the secondary sensor and my AEM wideband was reading exactly what 034's dyno wideband was showing. The secondary O2 sensor needs to be plugged in no matter what, even if it's written out. NOTE: Keep the removed O2 sensor away from any plastic or rubber parts because it does get hot. It has a heating element inside and when the car is on it will get hot. Just make sure it's hanging in the air with nothing near it within 3 inches or so to make sure it doesn't touch anything.