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

[blue62]

Cats fail in a number of ways.
1. Physical damage such as hitting speed bumps. Can lead to a rupture,hole, leak in the case.
2. "Plugging up" usually caused from things like too rich of mixture over time. rings not seating causing oil blow by, leaking head gasket. Antifreeze gets into the exhaust.
3."Burning out" caused by to lean of mixture, excessive idle time, things that create to much heat.
A burned up cat has no back pressure issues or the like, it acts just like a good cat except it doesn't do it's thing.
Those are the things I am aware of.

They are designed to last the life time of the car. But they function in a very narrow range. So fuel air ratio needs to be very close to 14.7 to 1. I think somewhere around one half of one percent + or - of 14.7 to 1. Outside that range for extended periods then they burn up or plug up.

So something to try and keep in mind when dealing with OBDII and the P-Codes.
Its not about engine performance or power or gas mileage. The primary function of the OBDII system including the sensors is Catalytic Converter Performance and longjevity. Everything else is secondary.

[porschefan76]

Originally Posted by blue62

Cats fail in a number of ways.
1. Physical damage such as hitting speed bumps. Can lead to a rupture,hole, leak in the case.
2. "Plugging up" usually caused from things like too rich of mixture over time. rings not seating causing oil blow by, leaking head gasket. Antifreeze gets into the exhaust.
3."Burning out" caused by to lean of mixture, excessive idle time, things that create to much heat.
A burned up cat has no back pressure issues or the like, it acts just like a good cat except it doesn't do it's thing.
Those are the things I am aware of.

They are designed to last the life time of the car. But they function in a very narrow range. So fuel air ratio needs to be very close to 14.7 to 1. I think somewhere around one half of one percent + or - of 14.7 to 1. Outside that range for extended periods then they burn up or plug up.

So something to try and keep in mind when dealing with OBDII and the P-Codes.
Its not about engine performance or power or gas mileage. The primary function of the OBDII system including the sensors is Catalytic Converter Performance and longjevity. Everything else is secondary.

Hey again! I'm not concerned about failure mode 1 as this hasn't occurred. I have a troubleshooting methodology for 2 (back-pressure test) and the fact that for about 75% of the time at constant RPM the downstream O2 do exhibit a flat response, I'm fairly confident that the cats are not burnt-out. Combine that with the temperature testing I have done which showed marked increase in flange temperature downstream of the cat compared to the cat inlet, I'm "fairly" confident they're not fully gone, but cannot say with confidence they're not currently compromised. I will research the tests for troubleshooting and verifying a "burned out" cat, but so far, haven't found anything. Are you aware of a way to verify "burned out" that doesn't rely on the output of an O2 sensor of unknown functionality (i.e. downstream O2 sensor may have it's own problems being 20 years old)?

Thank you for the continued help and ideas!

[blue62]

Originally Posted by porschefan76

Hey again! I'm not concerned about failure mode 1 as this hasn't occurred. I have a troubleshooting methodology for 2 (back-pressure test) and the fact that for about 75% of the time at constant RPM the downstream O2 do exhibit a flat response, I'm fairly confident that the cats are not burnt-out. Combine that with the temperature testing I have done which showed marked increase in flange temperature downstream of the cat compared to the cat inlet, I'm "fairly" confident they're not fully gone, but cannot say with confidence they're not currently compromised. I will research the tests for troubleshooting and verifying a "burned out" cat, but so far, haven't found anything. Are you aware of a way to verify "burned out" that doesn't rely on the output of an O2 sensor of unknown functionality (i.e. downstream O2 sensor may have it's own problems being 20 years old)?

Thank you for the continued help and ideas!

The only way I know of to reliably test a Cat to see if it is burned out. (other then what the O2 sensor is showing). Is with something like a five gas analyzer. Some shops still have them. Or your local smog test station. That is one of the things smog test stations are testing when they put the probe up the exhaust pipe. They are looking at the gases from the exhaust to see if the Cat is working properly.

[porschefan76]

Originally Posted by blue62

The only way I know of to reliably test a Cat to see if it is burned out. (other then what the O2 sensor is showing). Is with something like a five gas analyzer. Some shops still have them. Or your local smog test station. That is one of the things smog test stations are testing when they put the probe up the exhaust pipe. They are looking at the gases from the exhaust to see if the Cat is working properly.

Ok, that ones going to have to wait until last then. It unrelated to P1126 so I'll get that fixed first and see where I stand. I suppose I can just run to the inspection station and run the car through at that point.

[porschefan76]

Hello all. Time for another update.

Things I've learned:
1. STFT is called Oxygen Sensor Integrator on my 986 01S (I think).
2. I reached out to Durametric regarding the discrepancy on P1126 between what Durametric was reporting "Porsche Fault Code 356 - Multiplic. mixture adapt. lower load range B.1:" and Bentley "Porsche DTC 35 Oxygen Sensing Area 1 Cylinders 4-6 - rich mixture threshold". Durametric doubled down on bank 1, indicating their data was such:
a. P1126: "Oxygen sensing adaption, lower load range, bank 1."
b. P1126: "Fuel system multiplicative Bank 1, fuel trim limits exceeded."
c. P1126: "Fuel system multiplicative Bank 1, Range 2 (multipl. fault) load (rl) > threshold and air mass > threshold."
VERDICT: This response from Durametric combined with the change in engine feel after installing new Bank 1 fuel injectors, I'm calling this a Bank 1 code. Whether it's being tripped for range 1 rich or range 2 rich or lean, I'm not sure.

OK, on to some of the work I've completed since last check-in:
I removed the upstream O2 sensors one at a time and performed a back-pressure test on each bank. Both banks had nearly zero back pressure at idle and not much more at 2500 RPM (maybe .5-1 psi). I inspected upstream view of each cat with a borescope and verified they do not appear plugged, nor are they burned through or anything like that.
I left the new upstream O2 sensors in place and collected a lot of data. P1126 did return after about 50 miles of driving. Fuel trims are nearly identical for Bank 1 and Bank 2, RKAT is now roughly -3.5 and FRA is roughly 1.3, which causes me to question why I'm not receiving a code for Bank 2 as well?

Comparing a Normalized MAF signal (divided MAF signal by idle value of 15) to the Throttle Position Sensor 1, I got the following graph:



Not sure if this tracks similar to how blue62 described or not? Also during data collection, kept an eye on MAF outputs. Is the MAF supposed to reach up over 582 kg/h (& 3.58 V) at 5260 RPM? I'm not sure on what the correct values are but this one appears to be functioning to me (output responses to increase air flow).

Next warm day, the spark plug tubes go in. I'll post any updates after that.

Any input/thoughts/new troubleshooting is appreciated. Aside from investigating the EVAP component under Bank 2 intake manifold and attempting to evaluate the 2 electronic change-over valves (one SAI and the other for the resonance flap) I'm kind of out of ideas.

Edit: Forgot to mention, observed fuel economy has largely improved and seems back to normal.

[blue62]

Your MAF signal compared to the TPS signal looks normal to me.
So I believe you MAF is fine.
You say your fuel mileage is back up???
Improvements are good. Any idea what your MPG is currently???
Do you think the fuel mileage improvement is from changing the injectors???

[porschefan76]

Originally Posted by blue62

Your MAF signal compared to the TPS signal looks normal to me.
So I believe you MAF is fine.
You say your fuel mileage is back up???
Improvements are good. Any idea what your MPG is currently???
Do you think the fuel mileage improvement is from changing the injectors???

Hi blue62! I can't thank you enough for sticking through this with me.

Yes, fuel economy seems to have largely returned to earlier numbers. I do not have an absolute number, but I'd estimate it at about 20mpg (~75 miles per quarter tank). This is varied driving conditions while test driving. I can only attribute this change to the replacement of Bank 1 fuel injectors, because Bank 2 fuel injectors didn't seem to make much of a difference to engine performance or fuel economy. Regarding engine performance, most, if-not-all, of the cold-start idle weirdness has gone away.

I have no black smoke (rich condition) at idle, nor any soot on the tailpipes, and the exhaust does not smell of gasoline. The old O2 sensors had a mostly white-tan light coating, which seems normal. Also, my RKAT numbers for both banks have gone further negative to -3.5 since changing Bank 1 fuel injectors. Yet, I'm still only throwing code P1126.

I got a little fed up trying to decipher Durametric data, so I bought a bluetooth obd and android app to watch the new O2 sensors and the post-cat sensors (as well as STFT, this is before I figured out it's PID in Durametric). All four O2 sensors and the STFT values looked very much closer to the data from ScannerDanner's videos (flat line for the downstream O2 sensors and adaptation behavior from the upstream sensors) than anything I was able to plot from Durametric data. No conclusions drawn here, it's just the way it is. As I learn to use the Android app better, I will try to output data from there as well if you want a look.

This thread has gotten long, so I will post a roll-up (TLDR style) summary shortly to get a snapshot of the current situation and hopefully, something might jump out, because right now, I'm not sure where to go next. Thanks again!