Ares3985 Posted September 13, 2019 Share Posted September 13, 2019 Can a bad front o2 sensor cause lean at wot but not during regular driving? My tuner had me smoke test. Found nothing. I am checking fuel pressure tomorrow but he sent me the second map and wanted me to datalog and see if it was different. I never made it out of the garage. As soon as I started the car I got a cel for non communicating front o2 sensor. I have one on the way but I am wondering could that starting to fail the day before have caused it to go lean. Also would it cause soot? When I started the car at the time of the o2 failure. It shot soot all over the garage floor. I’ve never had any soot before. Obviously it’s from what’s going on w the a/f but wouldn’t that mean it was rich not lean? Idk maybe I’m wrong. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Max Capacity Posted September 14, 2019 Share Posted September 14, 2019 The front O2 is the one the is used to meter fuel flow. So if its not working correctly... 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Ares3985 Posted September 14, 2019 Author Share Posted September 14, 2019 The front O2 is the one the is used to meter fuel flow. So if its not working correctly... Awesome. Thanks Max! Hopefully that’s why I was lean and I can keep going on my tune. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
DaveWaters Posted September 14, 2019 Share Posted September 14, 2019 (edited) It’s my understanding that the o2 sensor is just sensing during wot and has no influence on fueling due to closed loop tuning. Meaning when you mash the pedal the ecu falls back on a preset tune (closed loop). Those here more versed in tuning please correct me if I’m wrong. Edit: now if the o2 sensor is not working properly I would imagine the ecu could throw a mil for lean condition when it’s actually not lean. Edited September 14, 2019 by DaveWaters Link to comment Share on other sites More sharing options...
Ares3985 Posted September 14, 2019 Author Share Posted September 14, 2019 Edit: now if the o2 sensor is not working properly I would imagine the ecu could throw a mil for lean condition when it’s actually not lean. I think you are right. I was thinking that also. he kept saying I’m lean but when the code popped I shot soot out my exhaust which has never happened. I’m thinking it wasn’t lean at all and it was reading improperly. He turned up the fuel and now it’s actual rich but doesn’t appear to be on a/f readings. Idk. Just makes sense I guess. We’ll find out. It comes later today. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Max Capacity Posted September 14, 2019 Share Posted September 14, 2019 Do you know the tricks to replace the sensor ? I put a screw type hose clamp around the O2 socket to keep it from spreading. Spray the old one with PB Blaster give it a few minutes to do its job. You'll need to pull the right front tire and the plastic panel. 305,600miles 5/2012 ej257 short block, 8/2011 installed VF52 turbo, @20.8psi, 280whp, 300ftlbs. (SOLD). CHECK your oil, these cars use it. Engine Build - Click Here Link to comment Share on other sites More sharing options...
Ares3985 Posted September 14, 2019 Author Share Posted September 14, 2019 Do you know the tricks to replace the sensor ? I put a screw type hose clamp around the O2 socket to keep it from spreading. Spray the old one with PB Blaster give it a few minutes to do its job. You'll need to pull the right front tire and the plastic panel. I never thought about that with the clamp. Good idea. I actually tried to pull It once before to check and was unsuccessful. This time I cut the wires and used a grinder to cut half the sensor off. Then was able to get a regular deep socket on it with impact. That o2 socket was pretty much useless if it’s stuck. Was just rounding it off. I’ll try the hose clamp trick next time. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
Ares3985 Posted September 14, 2019 Author Share Posted September 14, 2019 Ok Sensor is replaced. I actually replaced the downstream one also. I had a new one laying around so I figured it couldn't hurt. So here are my datalogs. One is from before I put the new one in. Before it even failed. This datalog is the one he said I was lean. The second is the one I just made with the new sensors. Someone give me some good news please lol.before o2 sensor wot.csvafter o2 sensor wot.csv Link to comment Share on other sites More sharing options...
BrandonspecB Posted September 15, 2019 Share Posted September 15, 2019 Is your front o2 in the stock location? The exhaust pressure there is too high to get an accurate reading under boost. The only way you can use the front o2 sensor to tune is if you move it after the turbo. You really need a wideband. Your tuner should know this. The front o2 is only used for fuel control during idling and cruise. As soon as you step on it, the ECU goes into open loop mode and ignores the o2 sensor feedback. The WOT AFR is completely dependent on the fuel flow and air flow calibration. There is no correction to it. Link to comment Share on other sites More sharing options...
Ares3985 Posted September 15, 2019 Author Share Posted September 15, 2019 (edited) Is your front o2 in the stock location? The exhaust pressure there is too high to get an accurate reading under boost. The only way you can use the front o2 sensor to tune is if you move it after the turbo. You really need a wideband. Your tuner should know this. The front o2 is only used for fuel control during idling and cruise. As soon as you step on it, the ECU goes into open loop mode and ignores the o2 sensor feedback. The WOT AFR is completely dependent on the fuel flow and air flow calibration. There is no correction to it. Yes it is in the stock location. He didn’t really specify why I was lean. Which value he was looking at. Just so happened that the o2 sensor failed during tuning. He recommended the fuel pressure test. Which I did last night. Not sure what my results mean but. I’m just gonna send him those new datalogs and hopefully they are better. Sent from my iPhone using Tapatalk Edited September 15, 2019 by Ares3985 Link to comment Share on other sites More sharing options...
BrandonspecB Posted September 15, 2019 Share Posted September 15, 2019 I looked at your logs and there is no difference in WOT AFR between the two. According to the log your AFR is 14:1 at WOT under boost. The thing is you can't trust that reading if the o2 is in the stock location. What I see in your logs is the AFR richens up like it's supposed to during spool up, but at peak boost it leans out. This is when exhaust pressure is going to be skewing the readings of the sensor. You need to have an o2 bung welded in after the turbo and move your front o2 there for tuning or get a wideband and set it up so you can datalog it. What the logs told me is that your o2 sensor is fine. Before you went WOT the fuel trims were doing what they were supposed to and weren't too far off from where they are supposed to be. Fuel trims are active during closed loop and this is when the o2 sensor is used for fuel correction. Link to comment Share on other sites More sharing options...
Ares3985 Posted September 15, 2019 Author Share Posted September 15, 2019 So do you think it isn’t actually going lean? The readings are just messed up? I sent 4 new wot short pulls to the tuner along with telling him I tested the fuel pressure and replaced my failed o2. Smoke tested and nothing. So I’m guessing next he’s going to tell me to get a wideband. If that is what happens he should have told me that from the start because I can’t be the first person that has exhaust pressure messing w readings. Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
BrandonspecB Posted September 15, 2019 Share Posted September 15, 2019 I don't think it's as lean as the logs show, but it's not possible to say for sure without putting the o2 in a lower pressure location. It's been known for a while that the front o2 readings get skewed toward lean under pressure: Front o2 readings Link to comment Share on other sites More sharing options...
Ares3985 Posted September 15, 2019 Author Share Posted September 15, 2019 I don't think it's as lean as the logs show, but it's not possible to say for sure without putting the o2 in a lower pressure location. It's been known for a while that the front o2 readings get skewed toward lean under pressure: Front o2 readings Might need to send that thread to the tuner lol. Well see what happens after he reads the new logs Sent from my iPhone using Tapatalk Link to comment Share on other sites More sharing options...
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