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

[blue62]

Originally Posted by porschefan76

OK, quick follow-up. I tested the temperatures of the "pre-cat" (cat on the header) and the temperatures were higher at the outlet end of the cats than at the inlet side, which is promising. I collected Durametric data for the O2 sensors while trying to hold the rpms at ~2000 RPMs for 2 minutes, followed by ~2500 RPM for 1 minute. The data is here:





The post catalytic converter O2 sensors appear to be responding properly, only showing big movements on throttle changes (to me at least. Please tell me if I am incorrect).
I went ahead and acquired a back pressure test gauge and O2 sensor socket and will attempt to check back pressure as soon as I am able. The weather is not going to cooperate this upcoming week.

As usual, thank you all for your time!

Post cat sensor response may be ok. Not really sure.
Very very difficult to diagnose problems over the internet.
Another issue in diagnosing is that the Durametric expresses data over units of time (bottom axis on the graphs) as compared to frames when you watch something like ScannerDanner's video's. Makes comparing data a little more difficult.

You may want to look at ScannerDanners vids on Catalytic converter efficiency or his vids related to the P0420 or P0430 codes. In most of his vids there are examples of bad and good wave forms on the graphs. May give you better insight then I am giving you
I know you don't have the P0420 or P0430 code but your post Cat Sensor signals still seem a little suspect.
Hope I am not leading you down a wrong path.

[porschefan76]

Originally Posted by Zzorro

Following with interest.

Thanks! Weather just got bad for about the next week, so updates may be slow.

Originally Posted by blue62

Post cat sensor response may be ok. Not really sure.
Very very difficult to diagnose problems over the internet.
Another issue in diagnosing is that the Durametric expresses data over units of time (bottom axis on the graphs) as compared to frames when you watch something like ScannerDanner's video's. Makes comparing data a little more difficult.

You may want to look at ScannerDanners vids on Catalytic converter efficiency or his vids related to the P0420 or P0430 codes. In most of his vids there are examples of bad and good wave forms on the graphs. May give you better insight then I am giving you
I know you don't have the P0420 or P0430 code but your post Cat Sensor signals still seem a little suspect.
Hope I am not leading you down a wrong path.

I definitely agree that the fidelity of the data from the durametric is troubling at times. The fact that the length of the time steps are inconsistent really gets to me. I will take in some more of ScannerDanner's videos and see if causes any ah-hah! moments. As soon as I can get those O2 sensors off and check the back pressure, that'll be a big data point on whether I need to focus on the exhaust to solve this issue or not.

Thanks again for following and helping!

[szube]

I encountered the same issues (and same P1126 code IIRC) with my 2.5L this past summer and tried many of the same steps you tried like cleaning, disconnecting the MAF, checking for vacuum leaks, O2 etc.

I know you said you checked the intake already, but its worth checking again between the airbox and the screen just downstream of the MAF (assuming the S's intake also has a screen).

FWIW, the culprit on my car turned out to be a clear piece of plastic wrapper caught inside the intake on the screen inside the intake tube just downstream of the MAF. I'd checked the intake previously but I didn't find it at first since the plastic was clear and not very large (maybe 1" -1.5" square) and it might've been clung to the side of the intake.

[porschefan76]

Originally Posted by szube

I encountered the same issues (and same P1126 code IIRC) with my 2.5L this past summer and tried many of the same steps you tried like cleaning, disconnecting the MAF, checking for vacuum leaks, O2 etc.

I know you said you checked the intake already, but its worth checking again between the airbox and the screen just downstream of the MAF (assuming the S's intake also has a screen).

FWIW, the culprit on my car turned out to be a clear piece of plastic wrapper caught inside the intake on the screen inside the intake tube just downstream of the MAF. I'd checked the intake previously but I didn't find it at first since the plastic was clear and not very large (maybe 1" -1.5" square) and it might've been clung to the side of the intake.

Hi! thanks for the suggestion, I will definitely look into that. If I'm being perfectly honest, other than checking that tube for smoke during my smoke test, I didn't investigate the intake tube very closely. As soon as the temps get back above 30 (ugg!), I will take a look and report back. As usual, thanks all for your time!

[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!

[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.

Sent from my POCOPHONE F1 using Tapatalk

[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.

Sent from my POCOPHONE F1 using Tapatalk

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!