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Old 08-24-2007, 12:33 PM   #1
williaty
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Join Date: Sep 2004
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Default How Do You Tell if an AFR/O2 Sensor is Broken?

So my car is down on fuel mileage and stinks like raw gas. I plugged into the ECU, and this is what the AFR sensor (front O2 sensor) reported for a full-throttle trip across the rev range:


Now, that seems a little wacky to me that the ECU would be letting the car go that rich. Do you think the AFR sensor could be at fault (even though I smell the car being rich)? If it's not a sensor, any idea why I'm running this rich?
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Old 08-24-2007, 01:13 PM   #2
Unabomber
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Your stock O2 sensor is about as accurate as calling my mom and asking for your AFRs, so don't get excited. If your O2 sensor was going south, you'd have a CEL. It might be on it's way out, so take it to the dealer and have them fix that crap for $0.
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Old 08-24-2007, 01:21 PM   #3
WRX_TR
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n/m......

Last edited by WRX_TR; 08-24-2007 at 01:21 PM. Reason: n/m didnt read right....rs
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Old 08-24-2007, 07:47 PM   #4
LewisWORX
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I have an innovate lc1 and I have to say that the stock o2 sensor is pretty spot on most of the time. I have run logs side by side with very little difference.
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Old 08-24-2007, 08:03 PM   #5
shemoves
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Well, 11.0 is actually pretty normal. Problem is, the stock 02 only reads down to either 11.2 or 11.02, so you don't really know how rich it is.

Due to the gas smell, I'd say your car is running rich. It may just be compensation from the ECU. If you don't mind having the dealer mess with it, by all means bring it in.

If you are more of a DIY guy, then do this: Run the current tank of gas out enough to where the gas light comes on. Refill it it with high quality (chevron, shell, etc) gas that is one 'step' up in octane (if you normally put in 87, put in 89. If you normally put in 89, do 91 or 93. If you normally do higher than 89, stop wasting your money). Reset the ECU. Then drive around and see if it goes away. (Reset ECU by unplugging the negative on the battery, pumping the brake a few times, and letting it sit for a couple minutes.) If it does go away, then you know the ECU detected something (coulda just been a bad batch of gas). From then on, just use good-quality 87, and you should be fine.

Oh yea, this is all assuming normal maintenance (filters, fluids, plugs) is current.
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