I’ve been having some issues with my upstream O2 sensors failing, and I’m trying to figure out what’s causing it. Car has no cat, runs a Racing beat intake, and a racing beat catback. No tune, just bolt-ons.

I have now replaced the upstream o2 sensor twice in the past year (Denso Oxygen Sensor 234-9102) and it seems as though the problem is getting worse.

I don't suspect any air leaks as the vacuum #'s look good I dont heavily premix.

Any ideas?

 

Do you have any pictures of the sensors you are taking out? Could be the wires, the sensor getting clogged/coated, or you are overtorquing it and damaging the sensor somehow.

Or its not even the sensor and there is another problem with the engine running. Compression, fueling, timing, or ignition coil spark wise.

 

What leads you to believe the sensor is failing? What codes is it throwing?

 

Here is a picture of the sensor.

Definitely not being over torqued. I'm inclined to think it might be fuel related. Engine was recently rebuilt and has 14k miles on it. Coils and plugs also have 14k miles on them.

I've been monitoring AFR's and it looks normal up until the point it fails

 

This is half the problem. I'm not getting an engine code but the AFR's spike and it has issues idling just before it completely fails. Throw in a new sensor and the car is good as new.

 

What about fuel trims? The ECU diagnoses the O2 sensor every drive cycle, it's one of the easiest failures to pop a code for, so the absence of a code tells me it's something else. Can you post the fuel trim and AFR data? How are you monitoring these things? Arr you taking apart the UIM to get to the sensor each time, and could that be what's actually causing/fixing the problem?

Is there oil in your intake?

 

I'll see if I can get logs of the AFR and fuel trim. I currently run Torque Pro so I can monitor data from my phone. I havent had to remove the upper intake manifold - the Upstream O2 is easily accessible and can be removed by lifting the car.

 

Here are some logs that include fuel trim and AFR data

 

The log doesn't show rpm or MAF rate, but it seems your sensor is working just fine and reading continuously. If the problem is the leaning out, have you considered you have a fuel delivery problem?
This looks like mostly an idle situation, how does it drive?

The constant +10 long term fuel trim is also indicative of a small but not insignificant vacuum leak.

Again, is there oil in the intake? What intake is on there?

 

I'll see if I can add the other data points. My guess is its fuel related and i'm looking at replacing the pump.

I drove around for 15 minutes when creating the logs and tried to get some variety in driving style. I also have this second data set with a little more info that i've attached.

Car drives fine. It had an odd issue the other day where it cut out completely trying to accelerate hard. Moderate driving was ok. That issue has since gone which had me thinking there's a fuel delivery problem.

AFR's are 14.5 or so highway and 13-14 when driving until the engine gets above 5k rpm and then i'll see as low as 11:1.

I'll check for vacuum leaks and will see what vacuum pressure reads at idle.

I dont recall seeing any oil in the intake but i'll pull it and verify that's still the case. Car has a racing beat intake on it

 

Cutting out under hard acceleration can be oil barfing into the intake due to blowby. Under medium load there's not enough blowby to force this.

Best logs for diagnosing is a fully warmed idle (airlfow grams/sec, rpm, fuel trim, AFR..) and a steady state cruise between 4 and 5k. In your case if there's an issue above 5 k try a steady state cruise at 6 or so and see what the logs say.

Unsteady driving logs are hard to parse, there's a lot going all at the same time.

 

Does anyone know what the port on the stock manifold is that is on the upper side between the middle and left bolt?

 

are you talking about the where the air pump is plumbed in?



thats where the pipe for the air pump goes. if you are catless most people remove it and block it off

 

yeah thats the one, thanks for your help, im pretty sure whatever was blocking it fell off then