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Old 10-22-2014, 11:21 PM   #1
Jaredhaney
Scooby Newbie
 
Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default AFR is Jumping From Rich to Lean Constantly SOLVED

So in one of my dumber moments I decided to degrease my engine bay for a second time since I washed my car. Since there is essentially a large water funnel on the hood and since the last time I washed the engine there were no ill effects, I decided why not. Well after letting the engine dry for two days before even turning on the engine, and now my air/fuel ratio has gone completely nuts and the car is acting like it attempting to correct itself constantly and making drastic corrections.

At idle the afr shows it jumping back and forth from about 11.5 on my wideband to 17 and making sweeps in between. It also continues to do this at steady throttle on the highway and with the cruise control on. Under WOT it acts completely perfect and whenever there is a decent load on the engine it clears up as far as I can tell from logs so something in closed loop setup seems to be on the fritz as if something may have gotten wet or shorted. It started immediately after I washed the engine.

The car currently has a catless downpipe, an aem short ram intake, and a protune from TopSpeed in Atlanta through my cobb accessport v3. I have cleaned the Maf, reset the ecu multiple times, tried swapping tunes, sandblasted the front o2 sensor, and so far have not found anything to change how it acts. I also unplugged every connector I could reach, sprayed contact cleaner in them, then added some dielectric grease and plugged them back in. Also got angry and shook some my CAI and top mount while it was idling to see if it would change any at all, which of course it did not. Anyone have any ideas on anything to try, because the maf seemed okay by my logs as far as voltage and reading air flow correctly?

Log of cruising, a pull through a couple gears, and then cruising in 6th:
https://docs.google.com/spreadsheets...kXY/edit#gid=0



Fix:
The front o2 had apparently gotten water in the connection and shorted. Put a new Denso o2 from the local parts store in and it was fixed immediately. Glad is finally fixed, it would almost make you sick driving it. Thanks NASIOC.
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Last edited by Jaredhaney; 10-24-2014 at 10:00 AM. Reason: Problem Solved
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Old 10-23-2014, 12:10 AM   #2
gsrcrxsi
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Member#: 236952
Join Date: Jan 2010
Chapter/Region: MAIC
Location: Baltimore
Vehicle:
2010 WRX (SSM)
Stg "2+" 300hp/360trq

Default

Replace your front O2 sensor.


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Old 10-23-2014, 09:08 AM   #3
Jaredhaney
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Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default

Thanks I'll order one today. I tend to not believe in coincidences but considering where it plugs in, I guess it shorted from the water.
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Old 10-24-2014, 09:58 AM   #4
Jaredhaney
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Member#: 379293
Join Date: Jan 2014
Location: Northeast Georgia
Vehicle:
2005 Subaru Sti
Silver

Default

Front o2 was the problem! This thing has been giving me fits all week without any real signs of what caused the AFR to be all over the place. Turns out that the sensor will still read and not throw a check engine light while being on the fritz.
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Old 10-24-2014, 10:55 AM   #5
gsrcrxsi
Scooby Specialist
 
Member#: 236952
Join Date: Jan 2010
Chapter/Region: MAIC
Location: Baltimore
Vehicle:
2010 WRX (SSM)
Stg "2+" 300hp/360trq

Default

very common issue. glad it helped you out. I had the same problem during cruising and it took me a while to track down the problem.

it makes sense. if you have no problems in WOT (open loop), but problems cruising light throttle or idling (closed loop), its easy to deduce the problem. whats the difference between open loop and closed loop? the input from the front o2 sensor! closed loop uses it, open loop ignores it.

you are correct, what's happening is that o2 sensor is feeding the ECU incorrect AFR readings, and the ECU is trying to correct for them, which in turn causes an incorrect response from the ECU. the absence of a CEL makes this more frustrating to pinpoint.
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