Help me solve this riddle, 02 sensor from hell.

[pcv86]

Ok, i love my legacy and all but im about to drive it over a cliff and watch it burn.

Heres the problem. The car has been running without an o2 sensor for a long time. I say a year. The previous owner (Project_legacy) bought a o2 sensor from the junk yard, installed it in his car and it has a huge hesitiation when boosting. Like it takes a while for the rpms to build up. It seem like it didnt have any power. But when he removed the o2 sensor. It had plenty of power.

Now this riddle is in my hands. I bought a new bosch o2 sensor for the ej22t. Because we both thought that o2 sensor he bought at the junkyard was shit anyways. I installed the NEW o2 sensor and there we have it. Same problems. And when i take it off the problems disappear.

Im thinking that it is ECU related. Since the ECU has been running without an o2 sensor for so long it has store that information in its memory FOREVER. YES, i reset the ecu multiple times.

Now, if your smart enough. Help me solve this riddle. Look at this picture hopefully it will inspire you to write me back on this problem.

[Threshld1]

I had this same problem where no matter what i did it would still run better (though a bit rich) with the o2 unplugged. Even after i bought a 4 wire and hooked it up. I was getting good readings on the scan tool but still hessitated like crazy. After some seafoam i found some pre-turbo exhaust leaks, fixed them and it seemed to help the problem significantly. I now am able to run it with the o2 connected though i still get the occasional mis though i think i still have a leak i havent been able to track down.

Oh and im running a WRX IC, turbo, bellmouth catless system and have the o2 way down stream without a CEL fix and no lights. Though i would only throw a light once a week with it not connected anyways.

[pcv86]

I had this same problem where no matter what i did it would still run better (though a bit rich) with the o2 unplugged. Even after i bought a 4 wire and hooked it up. I was getting good readings on the scan tool but still hessitated like crazy. After some seafoam i found some pre-turbo exhaust leaks, fixed them and it seemed to help the problem significantly. I now am able to run it with the o2 connected though i still get the occasional mis though i think i still have a leak i havent been able to track down.

Oh and im running a WRX IC, turbo, bellmouth catless system and have the o2 way down stream without a CEL fix and no lights. Though i would only throw a light once a week with it not connected anyways.

So basically when you did the seafoam leak-down. There were exhaust leaks which threw off your o2 sensor. Exhaust leaks causes the o2 sensor to go crazy?? Interesting.. anyone elses input on this?

[Threshld1]

I should add i replaced my valve cover seals and bled my HLA's at the same time i did the uppipe to turbo and turbo to downpipe gaskets. I would get a second opinion on it but im quite sure an exhaust leak pre-o2 will cause false readings.

Do you notice the problem coming back occasionally even with the o2 unplugged? Unplugged mine would run great for a day but it would randomly come back and miss under high load

I think its worth atleast putting a can of sea-foam through the PCV and watching for any leaks before blaming the ECU. If you come up with something else please let me know

[pcv86]

I should add i replaced my valve cover seals and bled my HLA's at the same time i did the uppipe to turbo and turbo to downpipe gaskets. I would get a second opinion on it but im quite sure an exhaust leak pre-o2 will cause false readings.

Do you notice the problem coming back occasionally even with the o2 unplugged? Unplugged mine would run great for a day but it would randomly come back and miss under high load

I think its worth atleast putting a can of sea-foam through the PCV and watching for any leaks before blaming the ECU. If you come up with something else please let me know

Hmmm. The thing with my exhaust is that its all welded together.. even the cat. Im missing one bolt that goes on the downpipe to turbo exhaust housing. That might be it (i hope so) Hopefully i can find a local memeber and test his ecu on my set up. For some reason i dont think a simple exhaust leak would throw off the o2 sensor erradically. It doesnt make sense to me.

[pcv86]

Thank you threshld1.. i tighten up the bolts and the problem went away.. wow weird how subaru's work. Thank you thank you thank you!!!!!!!! i want to send u a thank you card.

[Threshld1]

haha no problem!
glad it was a repeatable solution

[gt tankie]

I had a similar problem turned out I had leaks in the ex manifold pre 02 sensor. Oxygen introduced into the ex manifold will throw the 02 sensor and with our ex arrangment there can be negative pulse passing through it. This can draw air into the manifold and cause problems (mean backfires too if ur running stinking rich!)

Gary

[thisgr8ride]

Is it safe to run with no 02 senser?

[head2wind]

I believe that the ECU defaults to Open Loop operation if the O2 sensor is disconnected. Safe? maybe, seems that others have ran for several years without issue other than overly rich mixtures.

Mine is doing a weird thing just prior to going closed loop. it won't run very well or much past 3k rpm, put the gas pedal anywhere still no good. I can hear the difference in the turbo whine (technical I know, but I don't have a boost gauge hooked up yet).... which just so happens to be about the same time I am trying to get on the highway! .... it runs hard when cold and then after it has ran for some time and is fully up to temp... but the transision from mildly warm to full temp is a PITA to drive through.

I think that a ECU/TCU reset and a new/different O2 sensor is in my near future.