P1126 and low rpm hesitation - all troubleshooting listed- Help greatly appreciated!

[ike84]

Originally Posted by porschefan76

Hello friends. Sorry for the delay in updates, the weather has not been cooperating.

Yesterday was the first break in temperature so I scoped the intake tube as suggested and there were no obstructions. I moved on to replacing the fuel injectors on Bank 1 (immensely easier than on Bank 2). I actually noticed some positive change in the cold idle, throttle response and general feel of the motor overall. The engine felt noticeably smoother on the test drive and performed much like I remember it performing before this all began. In addition, fuel economy seemed to improve, but it was based on visual gauge estimation, so not data.

This is not the end of the road though. The car stored a P1126 during the test drive and there is still a momentary "swoosh" when sharply pressing the throttle.

It looks like the weather will be improving again next week sometime, so I'll check the cats by removing the fore O2 sensor and checking back pressure on each side. I'll also try smoking the intake again. I also noticed that cylinder 1 appears to have begun leaking oil at the spark plug tube, so I'll be replacing all 6 of those as well (they're on their way).

I do have a question though regarding P1126. Can anyone give me the correct verbiage for P1126 on DME 7.2? I realized my Durametric is reporting it as P1126 - Porsche fault code 356 - Multiplic. mixture adapt. lower load range B.1: and the Bentley manual reports it as P1126 Porsche DTC 35 - Oxygen sensing area 1 cylinders 4-6 - Short to B+/above upper limit/rich mixture threshold. Is P1126 a Bank 1 or Bank 2 code on 7.2? Any help there is appreciated!

I'm also planning to do a "hard reset" and capture some fresh data. Can anyone with a Durametric and DME 7.2 tell me what the short term fuel trim entry is? I was under the impression it would be "oxygen sensing Lamba" or "fuel trim mean value" but I do not see either in the list of Actual Values.

As usual, thank you for your time and help!

Hey fan, late to the party but I have a couple of thoughts...

Intake backfire is a lean condition (so long as timing is not completely wrong, which would be impressive), and if your o2 sensors are reading rich at that time if be would be very suspicious. A new set is not expensive, it may be worth a try.

Are you still pulling vacuum at your oil fill tube? May be worth double checking - i have read (not personally experienced though) that if you lose vacuum to aos then your crankcase pressure will build up and the you will notice this when the plug tubes start to leak oil.

Occam's razor - fouled o2 sensors reading too rich, engine pulls fuel in response, lean condition causes intake backfire (at idle only as the system will run richer under load), fries AOS tube, created vacuum leak, lean condition is now worsened and plug tubes are leaking oil. New injectors may have helped band aid the problem but I don't think they were the chicken or the egg.

Anyway, just a thought.

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[porschefan76]

Originally Posted by ike84

Hey fan, late to the party but I have a couple of thoughts...

Intake backfire is a lean condition (so long as timing is not completely wrong, which would be impressive), and if your o2 sensors are reading rich at that time if be would be very suspicious. A new set is not expensive, it may be worth a try.

Are you still pulling vacuum at your oil fill tube? May be worth double checking - i have read (not personally experienced though) that if you lose vacuum to aos then your crankcase pressure will build up and the you will notice this when the plug tubes start to leak oil.

Occam's razor - fouled o2 sensors reading too rich, engine pulls fuel in response, lean condition causes intake backfire (at idle only as the system will run richer under load), fries AOS tube, created vacuum leak, lean condition is now worsened and plug tubes are leaking oil. New injectors may have helped band aid the problem but I don't think they were the chicken or the egg.

Anyway, just a thought.

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Hello and thanks for joining in! I really appreciate the ideas. I've tried to use as few assumptions as possible while troubleshooting, so I like the application of Occam's Razor, but I'm not sure the data matches the assertion. I'll try to explain my approach below.

I have considered just changing the O2 sensors many times since this started as they're so cheap, but I resisted because according to Durametric, it all appeared to be working as intended (to me at least). The FORE cat O2 sensors were responding with a sine wave and the fuel trims seemed to be adapting by removing fuel at idle and adding it under load. I have never been able to get them to "peg rich" or "peg lean". Now, considering your comments, for the O2 sensors to be working properly, wouldn't it make sense for them NOT to be operating as a full range sine wave UNTIL the trims have adjusted? Do O2 sensors have a failure mode like this?

Shouldn't they be indicating either rich or lean through altered sine amplitude until after the adjustment? I have data that shows the O2 sensor output is essentially unchanged even as the RKAT value is changing. Some insight here would be invaluable. Perhaps it's because the amount of trim being added isn't that large (RKAT ~1.5-3.0 and FRA is ~1.25)? This is part of why I'm trying to find the short term fuel trim within Durametric, to compare with the O2 sensor output.

Looking back, I have specifications from Porsche I have cobbled together from this site and others and it looks like the O2 sensor range is 0.04mV less than or equal to "O2 Sensor Volts" less than or equal to 0.79 mV. I do have O2 output data with some values above 0.79mV, however in ScannerDanner's youtube videos, there are times he has said this doesn't matter much.

Can anyone confirm that 0.79mV is the proper hard limit for O2 output using Durametric Tool for a 986 01S?

Regarding the crankcase pressure, I've tested with a manometer and I am pulling -5.05 inches of water column, which is what it appears I should be getting. I honestly think the oil on the valve cover at the spark plug tube (this oil residue is new) is likely due to O-ring failure but, I'll put the manometer back on the oil-fill tube next time the weather cooperates.

I would be overjoyed to simply replace the AOS and the O2 sensors and be done, but I've done my best to avoid changing things that "appear" to be operating properly. If I can nail down an analysis that shows the O2 sensors are not performing correctly, I'll replace them.

Additional questions, what should the "Engine Load %" be at idle in Durametric? My data seems to indicate 19.00-20.25 at idle? Is this correct? If not, what does this point toward?

I'm open to any ideas on further troubleshooting! Also, I have no problem replacing the O2 sensors if the values above 0.79 mV indicate they're failing. Thank you all for your continued help!

[ike84]

Originally Posted by porschefan76

Hello and thanks for joining in! I really appreciate the ideas. I've tried to use as few assumptions as possible while troubleshooting, so I like the application of Occam's Razor, but I'm not sure the data matches the assertion. I'll try to explain my approach below.

I have considered just changing the O2 sensors many times since this started as they're so cheap, but I resisted because according to Durametric, it all appeared to be working as intended (to me at least). The FORE cat O2 sensors were responding with a sine wave and the fuel trims seemed to be adapting by removing fuel at idle and adding it under load. I have never been able to get them to "peg rich" or "peg lean". Now, considering your comments, for the O2 sensors to be working properly, wouldn't it make sense for them NOT to be operating as a full range sine wave UNTIL the trims have adjusted? Do O2 sensors have a failure mode like this?

Shouldn't they be indicating either rich or lean through altered sine amplitude until after the adjustment? I have data that shows the O2 sensor output is essentially unchanged even as the RKAT value is changing. Some insight here would be invaluable. Perhaps it's because the amount of trim being added isn't that large (RKAT ~1.5-3.0 and FRA is ~1.25)? This is part of why I'm trying to find the short term fuel trim within Durametric, to compare with the O2 sensor output.

Looking back, I have specifications from Porsche I have cobbled together from this site and others and it looks like the O2 sensor range is 0.04mV less than or equal to "O2 Sensor Volts" less than or equal to 0.79 mV. I do have O2 output data with some values above 0.79mV, however in ScannerDanner's youtube videos, there are times he has said this doesn't matter much.

Can anyone confirm that 0.79mV is the proper hard limit for O2 output using Durametric Tool for a 986 01S?

Regarding the crankcase pressure, I've tested with a manometer and I am pulling -5.05 inches of water column, which is what it appears I should be getting. I honestly think the oil on the valve cover at the spark plug tube (this oil residue is new) is likely due to O-ring failure but, I'll put the manometer back on the oil-fill tube next time the weather cooperates.

I would be overjoyed to simply replace the AOS and the O2 sensors and be done, but I've done my best to avoid changing things that "appear" to be operating properly. If I can nail down an analysis that shows the O2 sensors are not performing correctly, I'll replace them.

Additional questions, what should the "Engine Load %" be at idle in Durametric? My data seems to indicate 19.00-20.25 at idle? Is this correct? If not, what does this point toward?

I'm open to any ideas on further troubleshooting! Also, I have no problem replacing the O2 sensors if the values above 0.79 mV indicate they're failing. Thank you all for your continued help!

Sorry but I really can't comment on the specifics about the durametric readouts. My knowledge of afrs is limited to use of wide band o2 sensors and afr or lambda readouts, and narrow band sensors like ours can be very finicky. With that being said though my experience in working on cars has been two things 1 - it's really easy to overthink these types of problems 2 - you can spend forever looking up detailed specs, reference values, etc when that time may have been spent turning wrenches. I'm not knocking your approach at all, but rather criticizing all the time I have spent doing that exact thing when all I really needed to do was start physically working through things on the vehicle. The theory behind ICEs is really quite simple, and all things revolve around a few basic principles that will lead you to a diagnosis in nearly all circumstances. (I'm sure you've heard it before but don't lose the forest through the trees lol) I'm totally with you that the "eh let's replace this part and see what happens" approach is fool hearted at best but i trust the processes of reason and elimination more than anything when it comes to complex problem solving. Not to mention that Amazon's return policies are great, so try a new part and if it doesn't fix the problem clean it up and send it back and then let someone else buy it at a great discount lol.

Anyway, I'm happy to help if I can. Good luck and keep us posted!

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[porschefan76]

Originally Posted by ike84

Sorry but I really can't comment on the specifics about the durametric readouts. My knowledge of afrs is limited to use of wide band o2 sensors and afr or lambda readouts, and narrow band sensors like ours can be very finicky. With that being said though my experience in working on cars has been two things 1 - it's really easy to overthink these types of problems 2 - you can spend forever looking up detailed specs, reference values, etc when that time may have been spent turning wrenches. I'm not knocking your approach at all, but rather criticizing all the time I have spent doing that exact thing when all I really needed to do was start physically working through things on the vehicle. The theory behind ICEs is really quite simple, and all things revolve around a few basic principles that will lead you to a diagnosis in nearly all circumstances. (I'm sure you've heard it before but don't lose the forest through the trees lol) I'm totally with you that the "eh let's replace this part and see what happens" approach is fool hearted at best but i trust the processes of reason and elimination more than anything when it comes to complex problem solving. Not to mention that Amazon's return policies are great, so try a new part and if it doesn't fix the problem clean it up and send it back and then let someone else buy it at a great discount lol.

Anyway, I'm happy to help if I can. Good luck and keep us posted!

Sent from my POCOPHONE F1 using Tapatalk

Hey, thanks for the quick response. I've got to admit, I am beginning to be tempted toward just replacing a few things (especially the low-dollar stuff) and see what happens.

I think if I can't get specifics on where the O2 output signals should be or what the STFT PID is in Durametric, this limits my ability to continue troubleshooting with any reliable effectiveness. But I cannot find any confirmation that maintaining a full-sweep sine wave of 0.04mV to 0.85 mV is even a failure mode for narrow-band O2 sensors, meaning logically, they're working and it's something else. That said, after I test the cats with a back-pressure gauge, replace the spark plug tubes, test crankcase vacuum with my manometer again and smoke the intake once more, my next step may be replacing the O2 sensors. Fortunately, I enjoy working on the car and learning more about it, so I'm just going to keep at it.

Thanks for the time and the help!

[blue62]

Originally Posted by porschefan76

Hey, thanks for the quick response. I've got to admit, I am beginning to be tempted toward just replacing a few things (especially the low-dollar stuff) and see what happens.

I think if I can't get specifics on where the O2 output signals should be or what the STFT PID is in Durametric, this limits my ability to continue troubleshooting with any reliable effectiveness. But I cannot find any confirmation that maintaining a full-sweep sine wave of 0.04mV to 0.85 mV is even a failure mode for narrow-band O2 sensors, meaning logically, they're working and it's something else. That said, after I test the cats with a back-pressure gauge, replace the spark plug tubes, test crankcase vacuum with my manometer again and smoke the intake once more, my next step may be replacing the O2 sensors. Fortunately, I enjoy working on the car and learning more about it, so I'm just going to keep at it.

Thanks for the time and the help!

From what I see in your O2 signal sine waves that you have posted in this thread in post 13 your O2 sensors are fine they show a typical sine wave.
The issue I see is your post Cat O2 signals are showing that your Cats are not working properly. So the Catalytic converter are suspect the sensors are fine.

Sorry I just went through the thread again and see in post 17 that you ran the O2 sensor data again at a more steady rpm.
But to me your bank 2 post O2 cat sensor still shows that your cat on bank 2 is suspect. maybe not failed but boarderline.

[ike84]

Originally Posted by blue62

From what I see in your O2 signal sine waves that you have posted in this thread in post 13 your O2 sensors are fine they show a typical sine wave.
The issue I see is your post Cat O2 signals are showing that your Cats are not working properly. So the Catalytic converter are suspect the sensors are fine.

Sorry I just went through the thread again and see in post 17 that you ran the O2 sensor data again at a more steady rpm.
But to me your bank 2 post O2 cat sensor still shows that your cat on bank 2 is suspect. maybe not failed but boarderline.

Hey blue do you think a failing cat would cause his problems though? I could see that if a cat were clogged and not flowing well that would cause loss of power because of choking down flow. Would out cars attempt to lean out the mixture in order to reduce emissions if it senses a bad cat? I'm not asking to disagree, it's purely from ignorance I've not ever dealt with a bad cat before and I'm trying to piece together how that would play into what he's dealing with.

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[blue62]

Originally Posted by ike84

Hey blue do you think a failing cat would cause his problems though? I could see that if a cat were clogged and not flowing well that would cause loss of power because of choking down flow. Would out cars attempt to lean out the mixture in order to reduce emissions if it senses a bad cat? I'm not asking to disagree, it's purely from ignorance I've not ever dealt with a bad cat before and I'm trying to piece together how that would play into what he's dealing with.

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1. I do not see a failing Cat causing his problems.
2.Our cars do not attempt to lean out the mixture in order to reduce emissions if they sense a bad Cat. Post Cat sensors on cars of that era do one thing = monitor Cat health via reading oxygen levels.
The only thing a narrow band O2 sensor of that era can do is sense oxygen and only in a very narrow band.
3. The reason I pointed what I see as possible failing or bad Cats is that he was talking about replacing his 02 sensors. I was pointing out that based on what I see in the O2 sensor Sine Wave, that the Sensors are fine. But the post Cat signal is suggesting a failing Cat.. So no need to replace the O2 sensors.

Ummm I think that's it Hope I answered your questions.
And there is nothing wrong with disagreeing how else could one learn he was wrong

[porschefan76]

Originally Posted by blue62

From what I see in your O2 signal sine waves that you have posted in this thread in post 13 your O2 sensors are fine they show a typical sine wave.
The issue I see is your post Cat O2 signals are showing that your Cats are not working properly. So the Catalytic converter are suspect the sensors are fine.

Sorry I just went through the thread again and see in post 17 that you ran the O2 sensor data again at a more steady rpm.
But to me your bank 2 post O2 cat sensor still shows that your cat on bank 2 is suspect. maybe not failed but boarderline.

Originally Posted by ike84

Hey blue do you think a failing cat would cause his problems though? I could see that if a cat were clogged and not flowing well that would cause loss of power because of choking down flow. Would out cars attempt to lean out the mixture in order to reduce emissions if it senses a bad cat? I'm not asking to disagree, it's purely from ignorance I've not ever dealt with a bad cat before and I'm trying to piece together how that would play into what he's dealing with.

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Hello and thanks for the follow-ups. Yes, I intend to back pressure test for failing cats when the weather cooperates, probably early this upcoming week. As far as I can tell however, the post-cat O2 sensor does not play with the ECU, so I don't think that could be causing the P1126, but maybe if the cat is failing, that could cause it?

I'll add results as soon as I perform the test. Thanks for the continued interest and inputs!

[blue62]

Originally Posted by porschefan76

Hello and thanks for the follow-ups. Yes, I intend to back pressure test for failing cats when the weather cooperates, probably early this upcoming week. As far as I can tell however, the post-cat O2 sensor does not play with the ECU, so I don't think that could be causing the P1126, but maybe if the cat is failing, that could cause it?

I'll add results as soon as I perform the test. Thanks for the continued interest and inputs!

Agree your P1126 is another issue.
Perhaps some form of vacuum leak.
Or MAF sensor but there are ways to test it.