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Old 12-11-2011, 12:04 AM   #1
Scooby Newbie
Member#: 65876
Join Date: Jul 2004
Chapter/Region: TXIC
Location: Austin, Tx
06 Stg 2 WRX Wagon

Default Easy way to tell if o2 sensor is going bad?

Hey guys--

I've done a few hours of searching between here and RR forum, and haven't been able to find an answer to this yet.

Is there an easy way to tell if my front o2 sensor is going bad based on logging parameters in RomRaider?

Obviously i will need to stay in closed loop operation as I understand that the ecu uses the maf for open loop fueling, but what parameters should I log, and what values should I be experiencing during normal operation of the o2 sensor? I unfortunately do not have a wideband currently.

Reason for the question is due to some terrible mpg's over the last month or two. No CEL's, just really bad mileage (16-17 mpg when I have averaged 20-24 like clockwork since owning the car, depending on how I drive of course.)

I've got some new plugs in the mail, and plan on cleaning the MAF soon just in case it got borked by some filter oil.

Car is a 2006 WRX wagon with 73k on the odometer. Mods are:
- TGV deletes
- bellmouth catless downpipe
- k&n panel filter
- silicone inlet
- xpt stg 2 map
- Tire pressure is 40 psi (55 psi max with these tires)

Here is a link to my thread on the romraider forum that has a couple Learning View screenshots and logs; one WOT, and one cruising. BTW, I have a small hole in my inlet so I'm sure that is why my fuel trims are a bit off in my learning view screens, but pretty sure thats not the only reason I'm seeing this kind of mpg's -->

That's all the info I can think of for now... Any help is greatly appreciated!
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Old 12-12-2011, 04:52 PM   #2
Scooby Guru
Member#: 36033
Join Date: Apr 2003
Chapter/Region: SCIC
Location: Tuning Lab
CEO PhatBottiTuning
2006 STi GTX3582 + Meth


if your front 02 sensor is going bad your car will start hesitating and bucking like a rodeo bull.

simply unplug the front 02 sensor connection by the stock boost controller and go drive around. if the bucking/hesitation is gone, then your front 02 is the culprit.
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Old 12-12-2011, 07:44 PM   #3
Scooby Newbie
Member#: 65876
Join Date: Jul 2004
Chapter/Region: TXIC
Location: Austin, Tx
06 Stg 2 WRX Wagon


^^Thanks for the reply, I havent experienced any hesitation-- car runs smooth, Ill try unplugging it and take a spin. Also, for anyone else concerned with a topic similar to this; here is a reply I recwived on RR forum:

"Well judging by your AF learning ranges your car isn't adding a ton of fuel, so I don't believe this is due to a bad o2 sensor. It could likely be a change in environmental conditions. I get much worse fuel economy in the winter.

If you really want to test your o2 sensor, spray something flammable into your turbo inlet (starting fluid, carb cleaner, etc.) and log AF correction. As soon as you spray in the fluid you should see it start to pull fuel. Alternatively, you can create a vacuum leak, and log the same parameter and see if it starts adding fuel to compensate for the increased oxygen entering the engine.

Hope this helps.


^will try this as well and let you know what I find.
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