Stuck in Open Loop?

[RedFRS4me]

Originally Posted by steve99

If you want to eliminate the tune then get a stock rom and use romraider to set the P0420 cel code (cat efficiency) to disabled.


then run the modded stock tune and see if you get same problem.

The problem is I ran stock tune and code P0420 shows up but I still have the same issue with AFR dipping to low 13s. I park the car and the next day its back to normal. I drive it in stop and go traffic and it doesn't do it. Only when I stay at 60mph+ for longer than 30 mins that I start seeing the AFR dip slowly till I get stuck in open loop. LTFT and STFT stay 0% Just like OP

[steve99]

Originally Posted by RedFRS4me

The problem is I ran stock tune and code P0420 shows up but I still have the same issue with AFR dipping to low 13s. I park the car and the next day its back to normal. I drive it in stop and go traffic and it doesn't do it. Only when I stay at 60mph+ for longer than 30 mins that I start seeing the AFR dip slowly till I get stuck in open loop. LTFT and STFT stay 0% Just like OP

I think you still have problem with hardware then, like sensor/wiring/connector, bad earth maybe exhaust leak or possibly even ECU

[RedFRS4me]

Originally Posted by steve99

I think you still have problem with hardware then, like sensor/wiring/connector, bad earth maybe exhaust leak or possibly even ECU

I'm 100% sure you're right. Probably a secondary O2 failure or leak due to cross thread. When I installed them on my OFH I never bothered to see if it was cross threaded since the install to remove them and install was easy. Might have been an oversight on my part and now I'm just starting to see it now.

[steve99]

Originally Posted by RedFRS4me

I'm 100% sure you're right. Probably a secondary O2 failure or leak due to cross thread. When I installed them on my OFH I never bothered to see if it was cross threaded since the install to remove them and install was easy. Might have been an oversight on my part and now I'm just starting to see it now.

grab an M18 by 1.5 mm pitch thead tap and run it through the header 02 bungs, they seem to distort due welding. the sensors will screw in by hand all the way then. if the thread on sensor is damage you will need to replace it unfortunatly

[Wepeel]

Originally Posted by RedFRS4me

The problem is I ran stock tune and code P0420 shows up but I still have the same issue with AFR dipping to low 13s. I park the car and the next day its back to normal. I drive it in stop and go traffic and it doesn't do it. Only when I stay at 60mph+ for longer than 30 mins that I start seeing the AFR dip slowly till I get stuck in open loop. LTFT and STFT stay 0% Just like OP

I just resolved my issue (posted in the datalog review thread).
http://www.ft86club.com/forums/showp...postcount=1228

Turns out I needed a new rear O2 sensor. As part of my troubleshooting I unscrewed/screwed the O2 in and out a few times to make sure the threading was smooth and sensor flush (it was). So I knew it wasn't a sensor placement issue.

Also, before I bought a new sensor, a friend had an old O2 sensor laying around. Since it was free, I swapped that one in, and noticed the problem accelerated - it only took a few mins of cruise to start seeing the AFR's drop. I'm guessing that sensor was highly degraded (friend replaced it as part of troubleshooting larger issues, but it was old and had a lot of mileage).

So that demonstrated to me that a more degraded sensor could make the problem worse, and that the rear O2 performance had a pretty significant effect on AFR. I bought a new sensor and that fixed the problem - steady 14.7 cruise during extended 70+ mph cruise.

Keep in mind O2 sensor voltage always reported something reasonable and there were no codes thrown, so it's possible that these things can decay and affect performance without any other indication that something is wrong.

[theadmiral976]

Originally Posted by Wepeel

I just resolved my issue (posted in the datalog review thread).
http://www.ft86club.com/forums/showp...postcount=1228

Turns out I needed a new rear O2 sensor.
Keep in mind O2 sensor voltage always reported something reasonable and there were no codes thrown, so it's possible that these things can decay and affect performance without any other indication that something is wrong.

Did you replace with an OEM sensor? Similar to you, I've been noticing my commanded AFR trending down from ~14.7 during long drives at constant RPM. Specifically, the downward spiral starts at the 1.5 hour mark and drops ~0.3 units every 20 min thereafter. For me, my STFTs and commanded AFR haven't hit 0.0 and ~12.2 respectively, indicating open loop; however, I imagine that I'm headed for that soon enough.

I wonder why these rear O2 sensors are dying. Perhaps the altered heat transfer of the uncatted header (I have an OFH)? If so, I wonder if there are better aftermarket options for the O2 sensor?

[Wepeel]

Originally Posted by theadmiral976

Did you replace with an OEM sensor? Similar to you, I've been noticing my commanded AFR trending down from ~14.7 during long drives at constant RPM. Specifically, the downward spiral starts at the 1.5 hour mark and drops ~0.3 units every 20 min thereafter. For me, my STFTs and commanded AFR haven't hit 0.0 and ~12.2 respectively, indicating open loop; however, I imagine that I'm headed for that soon enough.

I wonder why these rear O2 sensors are dying. Perhaps the altered heat transfer of the uncatted header (I have an OFH)? If so, I wonder if there are better aftermarket options for the O2 sensor?

I replaced with an aftermarket Bosch, seems to work fine. It definitely sounds like you're on your way to open loop. Peculiar but it seems there are a few of us that are seeing the same behavior.

I was wondering why it would have failed too. I'm only at 32k miles and never hit or banged the sensor - I did swap it in a few times since I went through 3 leaky borla header warranty replacements before I finally got the OFH, although I never even had to apply that much torque to swap the O2 sensor. Since there is no cat it's getting hit with hotter/dirtier air, so maybe that does have something to do with it. Although if it was that I'd think we'd start seeing more failures from everyone who's running a catless header (or maybe they're just not monitoring AFR constantly). I guess time will tell how much longer the new O2 sensor lasts.

[theadmiral976]

Originally Posted by Wepeel

I replaced with an aftermarket Bosch, seems to work fine. It definitely sounds like you're on your way to open loop. Peculiar but it seems there are a few of us that are seeing the same behavior.

I was wondering why it would have failed too. I'm only at 32k miles and never hit or banged the sensor - I did swap it in a few times since I went through 3 leaky borla header warranty replacements before I finally got the OFH, although I never even had to apply that much torque to swap the O2 sensor. Since there is no cat it's getting hit with hotter/dirtier air, so maybe that does have something to do with it. Although if it was that I'd think we'd start seeing more failures from everyone who's running a catless header (or maybe they're just not monitoring AFR constantly). I guess time will tell how much longer the new O2 sensor lasts.

Thanks for the info. To add details to the discussion for future reference, I have only moved my O2 sensors once, when I installed my OFH over a year ago. They are definitely not cross-threaded, nor did I hit the sensors against the bung during install. I'm currently at 42k miles, with about 20k miles on the OFH. I monitor my trims pretty regularly and haven't noticed the commanded AFR dropping before the ~1.5 hour mark of constant RPM cruising on the highway. I regularly take 5-hour constant RPM trips, so perhaps if others aren't doing this, they would never notice the problem. Still not really sure how to mechanically/physically explain the timing, though (e.g. why it takes upwards of 90 minutes to see an effect).

I never saw this cAFR drop prior to installing the uncatted header (I ran OFT Stage 1 maps for about 12k miles prior to installing the OFH). Good to know that other uncatted headers seems to be causing the same issue.

[RedFRS4me]

Originally Posted by theadmiral976

Thanks for the info. To add details to the discussion for future reference, I have only moved my O2 sensors once, when I installed my OFH over a year ago. They are definitely not cross-threaded, nor did I hit the sensors against the bung during install. I'm currently at 42k miles, with about 20k miles on the OFH. I monitor my trims pretty regularly and haven't noticed the commanded AFR dropping before the ~1.5 hour mark of constant RPM cruising on the highway. I regularly take 5-hour constant RPM trips, so perhaps if others aren't doing this, they would never notice the problem. Still not really sure how to mechanically/physically explain the timing, though (e.g. why it takes upwards of 90 minutes to see an effect).

I never saw this cAFR drop prior to installing the uncatted header (I ran OFT Stage 1 maps for about 12k miles prior to installing the OFH). Good to know that other uncatted headers seems to be causing the same issue.

That's funny you said that because I didn't start seeing this until I ran the Stage 2OFH tunes that were just released. Or maybe I just never paid too much attention to my AFR running the previous tunes including E85 tunes and I'm just seeing this for the first time. In stop-in-go traffic this never happens to me. but if I'm constantly on the throttle at 70mph for more than 30 minutes the car will creep slowly until it's stuck in open loop.

And like OP stated, it may be related to the catless design allowing more heat and deposits to the secondary O2. Unlike the primary O2, It probably can't absorb heat or fails if it's exposed too long to the same heat the primary O2 sees. For this reason I didn't want to spend money on a new secondary O2 and have it fail over time prematurely. I ended up disabling my LTFT and ignoring secondary O2 feedback. I tested tonight and it's working flawlessly except I think I lost some power because if i'm below the closed loop threshold the car will not add fuel in open loop to any rpms until I actually hit close loop. Feels like a lack of throttle response under normal driving but once I see closed loop engaged power kicks in. But we'll see as the car relearns itself after a few days.

[Wepeel]

Originally Posted by theadmiral976

Thanks for the info. To add details to the discussion for future reference, I have only moved my O2 sensors once, when I installed my OFH over a year ago. They are definitely not cross-threaded, nor did I hit the sensors against the bung during install. I'm currently at 42k miles, with about 20k miles on the OFH. I monitor my trims pretty regularly and haven't noticed the commanded AFR dropping before the ~1.5 hour mark of constant RPM cruising on the highway. I regularly take 5-hour constant RPM trips, so perhaps if others aren't doing this, they would never notice the problem. Still not really sure how to mechanically/physically explain the timing, though (e.g. why it takes upwards of 90 minutes to see an effect).

I never saw this cAFR drop prior to installing the uncatted header (I ran OFT Stage 1 maps for about 12k miles prior to installing the OFH). Good to know that other uncatted headers seems to be causing the same issue.

There must be some logic to determine if the primary AFR or O2 sensor are bad, because if one is bad then your AFR readings are unreliable, and the car has no idea what is going on from a fueling/combustion standpoint. This is just a wild guess, but in steady state conditions like cruise, the ECU uses this time to do comparisons and make sure both are reporting somewhat similar AFR. There might be some kind of aggregate error that builds and as it builds the car targets richer and richer to make the car more safe, and one it crosses a certain threshold the car decides it's safest to just go open loop rich.

The healthier both sensors are, the lower the likelihood this will happen. And if a sensor is degrading, and continues to degrade, open loop will happen faster and faster. I suspect if a car has this problem that it will happen faster as the sensor degrades more.

^That's all a guess. But when I put an older, more questionable O2 in my car it didn't take long at all to hit open loop. My original bad sensor took about an hour at 70+ to hit open loop - this other bad one took 10 minutes at 55-60 to hit open loop, and the brand new sensor did a 2hr+ 70 mph cruise with perfect AFR.

The other thing I noticed with the OFH is that the AFR sensor is located to pick up readings off of only one bank, and the O2 is sensing after the full merge. That may have something to do with it?

[RedFRS4me]

Originally Posted by Wepeel

There must be some logic to determine if the primary AFR or O2 sensor are bad, because if one is bad then your AFR readings are unreliable, and the car has no idea what is going on from a fueling/combustion standpoint. This is just a wild guess, but in steady state conditions like cruise, the ECU uses this time to do comparisons and make sure both are reporting somewhat similar AFR. There might be some kind of aggregate error that builds and as it builds the car targets richer and richer to make the car more safe, and one it crosses a certain threshold the car decides it's safest to just go open loop rich.

The healthier both sensors are, the lower the likelihood this will happen. And if a sensor is degrading, and continues to degrade, open loop will happen faster and faster. I suspect if a car has this problem that it will happen faster as the sensor degrades more.

^That's all a guess. But when I put an older, more questionable O2 in my car it didn't take long at all to hit open loop. My original bad sensor took about an hour at 70+ to hit open loop - this other bad one took 10 minutes at 55-60 to hit open loop, and the brand new sensor did a 2hr+ 70 mph cruise with perfect AFR.

The other thing I noticed with the OFH is that the AFR sensor is located to pick up readings off of only one bank, and the O2 is sensing after the full merge. That may have something to do with it?

I curious as well about the second O2 location. But for now I'm driving on just the AF3 tables zeroed and the problem has gone away with no seconday O2 feedback interrupting my cruising AFR.

[theadmiral976]

Originally Posted by Wepeel

That's all a guess. But when I put an older, more questionable O2 in my car it didn't take long at all to hit open loop. My original bad sensor took about an hour at 70+ to hit open loop - this other bad one took 10 minutes at 55-60 to hit open loop, and the brand new sensor did a 2hr+ 70 mph cruise with perfect AFR.

The other thing I noticed with the OFH is that the AFR sensor is located to pick up readings off of only one bank, and the O2 is sensing after the full merge. That may have something to do with it?

That is definitely a reasonable hypothesis. Now the question is whether it is worth replacing the rear O2 sensor regularly or not? Or if there is an alternative sensor available that would be more resistant to fouling and/or thermal degradation. Replacing this sensor every 20k miles is certainly not ideal. Maybe as RedFRS4me said, there might be a way to modify the maps to "silence" this phenomenon; however, I am a little wary of that fix, mainly because I am not very knowledgeable about tuning.

[RedFRS4me]

Yij

Originally Posted by theadmiral976

That is definitely a reasonable hypothesis. Now the question is whether it is worth replacing the rear O2 sensor regularly or not? Or if there is an alternative sensor available that would be more resistant to fouling and/or thermal degradation. Replacing this sensor every 20k miles is certainly not ideal. Maybe as RedFRS4me said, there might be a way to modify the maps to "silence" this phenomenon; however, I am a little wary of that fix, mainly because I am not very knowledgeable about tuning.

With my OFT tune I added the airfuel #3 tables to my tunes and used rom raider to zero out those values. These relate to the ecu reading the secondary o2 to adjust/learn fuel which in our case, running rich open loop. With these zeroed I am no longer seeing the issue.

[theadmiral976]

Originally Posted by RedFRS4me

Yij

With my OFT tune I added the airfuel #3 tables to my tunes and used rom raider to zero out those values. These relate to the ecu reading the secondary o2 to adjust/learn fuel which in our case, running rich open loop. With these zeroed I am no longer seeing the issue.

That is brilliant! Excuse my naivete, but would you anticipate any long-term issues by doing this adjustment?