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Old 01-20-2015, 09:18 AM   #1
gsrcrxsi
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Default Burning up Front oxygen sensor every 6mo

Hey guys. I've been having a problem for about the last year. For some reason my car/engine/tune/something seems to be causing failures of my front O2 sensor. They seem to last about 6months before needing to be replaced again.

A little background.
2010 WRX
Stage 2"+"
-At about 103,000mi, my head gasket failed.
-During replacement, I had the motor rebuilt with forged Pistons and new bearings. (Including all necessary machine work, etc)
-Motor was put back together with a full-race header that is ceramic coated and wrapped with DEI 'titanium' heat wrap.
-The F-R manifold is a "1.5 scroll" meaning that the lower manifold is EL twin scroll and the up pipe is merged from twin to single with a stock location flange.
-The front O2 is located on the lower tube of the FR manifold, just before the up-pipe
-I also have a wideband O2 in the downpipe just after the turbine (Cobb downpipe location)

Shortly after the motor was built and re-tuned, I noticed that the car was surging at cruise. The readout from my wideband showed the AFRs fluctuating from ~12 to ~18 and would go up and down over and over when cruising at certain throttle positions/loads. I felt like I was chasing my tail looking for loose hoses and leaks, and finally narrowed it down to the front O2 causing the issue. The stock sensor had ~106,000mi on it at that point, so I said ok fine, prob needs replaced. Problem fixed, all is well.

Fast forward ~6mo to June 2014. Same issues start to pop up. Surging at cruise, fluctuating AFRs. Initially I discounted the O2 again because I had just replaced it. But I ended up replacing the sensor under warranty (the Denso sensors have a 12month warranty, FYI). I thought, maybe I just got bum sensor, it happens. Problem fixed, all is well.

Fast forward to now, 6-7mo later, and this problem has creeped up again. I've already purchased the replacement and will replace it again.

I'm using Denso 234-9035 sensors, which is the exact same sensor as OEM.

Any thoughts on what might be causing them to fail? Has anyone else had accelerated failure with the front O2 sensor on a stage 2 or more car? I do drive quite a bit so 6mo is about 15k miles for me. But still, I'd expect the sensor to last longer than that. I'm also not running any leaded fuels or oils with crazy amounts of zinc or additives that might otherwise foul the sensor. Gas primarily from Shell or Sunoco, and I've mainly been using Mobil1 0w40 oil.

I do not have an EGT gauge, but I'd expect slightly higher than normal EGTs given that the header is coated and wrapped to trap more heat in for increased efficiency. Anyone think that is the underlying cause? Or maybe the tune itself is causing higher EGTs and burning up the sensor?

Maybe even something else? I am planning to bring this up with my tuner as I'm going to have the car re-tuned anyway for other reasons. But I wanted to start a discussion on this and see if anyone else has similar experiences or thoughts.



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Old 01-20-2015, 05:30 PM   #2
sebi1990
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There is many causes for a o2 sensor to go bad. Is it a problem with the wiring to the O2 sensor? Or is the sensor itself malfunctioning. If you have a picture of the sensor that would help us determinate what might have caused it to fail.
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Old 01-20-2015, 05:54 PM   #3
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i had my front sensor go a while after i installed tomei el headers. they are wrapped with dei titanium.its been good since though. i used the same denso part number you did.
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Old 01-20-2015, 06:35 PM   #4
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Quote:
Originally Posted by sebi1990 View Post
There is many causes for a o2 sensor to go bad. Is it a problem with the wiring to the O2 sensor? Or is the sensor itself malfunctioning. If you have a picture of the sensor that would help us determinate what might have caused it to fail.
It's obviously not the wiring TO the sensor plug (ie the engine harness end of the wiring) as the problem is totally alleviated by replacing the sensor.

It is definitely the sensor itself malfunctioning. i'll take a pic when i get the sensor swapped out, but it's always the same looking. nothing really noteworthy.
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Old 01-20-2015, 06:41 PM   #5
gsrcrxsi
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I actually found my old sensor (the original OEM one) this sensor had about 106,000mi on it. But failed shortly after the new motor was installed. I wouldn't put too much weight on this one.



The second sensor had to be sent back to Denso for warranty replacement so I don't have it.


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Old 01-20-2015, 07:17 PM   #6
gsrcrxsi
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I'd also like to add that when these sensors "fail", its not a total failure. the sensor does not trip any codes. rather it seems to start feeding erroneous AFR data back to the ECU and the ECU begins trying to compensate (incorrectly) as a result.
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Old 01-20-2015, 09:19 PM   #7
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1. Do you have any exhaust leaks. Leaks before the sensor will burn them up.
2. Boost leaks? What are your AFRs?
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Old 01-20-2015, 09:36 PM   #8
gsrcrxsi
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Default Burning up Front oxygen sensor every 6mo

Actually. I just replaced the manifold gaskets yesterday as there has been a small leak on the passenger side header gasket for some time now.

How exactly does an upstream leak cause the sensor to burn up? I've seen plenty of people say that the leak can make the car think it's running lean, and adds fuel to compensate, and hurts MPG, but I haven't seen anything to suggest that the leak actually HURTS the sensor itself. Elaborate please.

Last edited by gsrcrxsi; 01-20-2015 at 09:56 PM.
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Old 01-20-2015, 09:39 PM   #9
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AFRs are "normal"
14.7ish in closed loop (cruise)
11.x ish in WOT open loop
Sliding scale at part throttle open loop.


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Old 01-20-2015, 11:09 PM   #10
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Got a pic of the O2 sensor in situ (that is, as it sits on the header when mounted in the car)?

O2 sensors have some specific mounting geometry; typically, the bung should be mounted above the horizontal plane so the sensor points in a generally "down" orientation. How is it mounted on your headers?

If the sensor is facing "up" it may be susceptible to contamination and damage from condensation in the exhaust pipe settling on it when things get are warming up and cooling down.
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Old 01-21-2015, 06:33 AM   #11
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It is horizontal. The same orientation as stock.


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Old 01-25-2015, 08:59 AM   #12
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Bump


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Old 01-26-2015, 08:43 PM   #13
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Leak would mean less air passing, thus less oxygen, computer thinks it is running lean, adds more fuel, thus it starts to run rich. Running rich would give significant unburnt fuel which would eventually clog the sensor. This is the reasoning I've come up with and read on other sources.

In addition, any time I've had a significant leak, it has burned up my O2 sensor pretty quick. I went through 2 early on when I owned the car with some pretty significant leaks. Fixed the leaks and stopped burning O2 sensors.

If you don't have any exhaust leaks, I would look at other things which would throw off the A/F ratio. Post MAF boost leaks, or bad MAF. I've done well with just cleaning my MAF and been able to fix most of my issues by fixing intake or exhaust leaks and swapping the plugs.
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Old 01-26-2015, 09:33 PM   #14
gsrcrxsi
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AFR readings from my wideband sensor have been normal though. maybe a tad on the lean side if anything. (in open loop)

after replacing the O2, the car seems to run richer.

kind of the opposite.
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Old 01-26-2015, 09:35 PM   #15
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...it almost sounds like contaminated fuel
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Old 01-26-2015, 09:39 PM   #16
gsrcrxsi
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across 1.5 years and multiple different stations?
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Old 01-26-2015, 11:08 PM   #17
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Quote:
Originally Posted by gsrcrxsi View Post
across 1.5 years and multiple different stations?

yeah...I know...but that is a weird one

maybe something you are doing that is causing this issue that you aren't thinking is causing it
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Old 01-26-2015, 11:33 PM   #18
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Quote:
Originally Posted by Uncle Scotty View Post
yeah...I know...but that is a weird one

maybe something you are doing that is causing this issue that you aren't thinking is causing it

Like fuel additives, or seafoaming frequently?

For sure exhaust leaks before or at the front O2 kill it quick, and new headers (ones that haven't been tanked) from the cosmoline/other gunk inside them.
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Old 01-27-2015, 05:30 AM   #19
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I don't use additives or sea foam.

I bought the header used. No "gunk" inside it.


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Old 01-27-2015, 09:01 AM   #20
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How is the grounding situation on your car? Maybe its not getting a good enough ground and is cause the sensor to die prematurely? I mean front O2 is one of the furthest runs from the ecu.
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Old 01-19-2016, 10:27 AM   #21
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Did you ever find a solution to this issue? I am currently experiencing the same thing. 09 Wrx/tomei headers/20g swap. I am on my 3rd front 02 sensor since installing the headers. Same crazy afr swings from 10-18 when they go. Otherwise the car runs beautifully.

I am wondering if there is some weight to delphi's suggestion about the grounding. I seem to remember a grounding strap to the headers or factory heat shield? That I couldn't re-use properly when I installed the headers. It was a long time ago so my memory is a bit fuzzy.
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Old 01-19-2016, 12:56 PM   #22
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Quote:
Originally Posted by Ashesofthewake View Post
Did you ever find a solution to this issue? I am currently experiencing the same thing. 09 Wrx/tomei headers/20g swap. I am on my 3rd front 02 sensor since installing the headers. Same crazy afr swings from 10-18 when they go. Otherwise the car runs beautifully.

I am wondering if there is some weight to delphi's suggestion about the grounding. I seem to remember a grounding strap to the headers or factory heat shield? That I couldn't re-use properly when I installed the headers. It was a long time ago so my memory is a bit fuzzy.
What kind of gaskets are you using on the header to head?
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Old 01-19-2016, 03:31 PM   #23
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What kind of gaskets are you using on the header to head?
I have a pair of the Grimmspeed thick gaskets on there now.
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Old 01-20-2016, 08:50 AM   #24
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Nope. Still happens. Actually need to replace it again soon
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Old 04-03-2020, 12:58 PM   #25
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Quote:
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Nope. Still happens. Actually need to replace it again soon
Hey, found the solution yet? Same exact problem as well, but while installing the new af sensor noticed a crack in the weld on my headers with carbon around it. So, I'll check there first.

Mike
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