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

[blue62]

Looking at the post Cat O2 signal I would say your cats are not working.
Post Cat signal is following RPM and Pre Cat signal very closely. Not as it should be.
Post Cat signal will have some rises and falls with RPM and engine load but should be biased towards a flatish signal voltage in the .650-.750 mil volt range.

There are some good youtube videos on testing for exhaust restrictions.
Also if you look up ScannerDanner on youtube he has some very good videos on reading fuel trims and O2 signals to diagnose performance problems.
He is a professional and very good at what he does.
You can view his videos and have a visual of what your Post Cat O2 signal should look like (flatish) under different running conditions.
Perhaps some of his videos will give you some insight on your issues.

[porschefan76]

Originally Posted by blue62

Looking at the post Cat O2 signal I would say your cats are not working.
Post Cat signal is following RPM and Pre Cat signal very closely. Not as it should be.
Post Cat signal will have some rises and falls with RPM and engine load but should be biased towards a flatish signal voltage in the .650-.750 mil volt range.

There are some good youtube videos on testing for exhaust restrictions.
Also if you look up ScannerDanner on youtube he has some very good videos on reading fuel trims and O2 signals to diagnose performance problems.
He is a professional and very good at what he does.
You can view his videos and have a visual of what your Post Cat O2 signal should look like (flatish) under different running conditions.
Perhaps some of his videos will give you some insight on your issues.

OK, I'm going to follow this and see where it leads. I've watched Schrodingers Box on youtube and he's where I got my primer on fuel trims, but ScannerDanner seems great as well. In fact, I'm watching this video now:
https://www.youtube.com/watch?v=9TlygJMxTps
I may go purchase a back pressure gauge and check each of the cats. The only hesitation I have with this right now, is that in ScannerDanner's video, he said that because the pre-cat O2 sensor indicates rich at wide-open throttle, he'll focus on the exhaust and assume it's not a fuel issue. It does not appear that I am running rich (likely lean) above idle. I also do not have a situation where the car will not exceed a certain speed. It still "almost" drives like it did before above 3000 RPM. Additionally, my water temperature gauge has never indicated that the engine was running hot.
I may start by checking the temperature of each cat at the inlets and outlets and ensure the outlet temperatures are higher than the inlet temperatures, indicating the cats are heating the gases. I will also try to capture a stream of good Durametric data from all 4 O2 sensors while maintaining 2000-2500 RPM for a minute or two. I will post results once I get a chance to run these tests, hopefully this afternoon. Thanks!

[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!

[Zzorro]

Following with interest.

[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!