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

[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

[ike84]

Originally Posted by blue62

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

So I need to go and watch scanner danners videos about cats because my knowledge of them is still very much comic book version. When they fail what is the main symptom? Do they choke down the exhaust and kill power through reduction of flow? Or do they just stop cleaning up the exhaust and result in no other difference? I remember newarts video of how he toasted his cats when he blew his engine but that's the only other time I've ever heard of them going bad.

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[porschefan76]

Originally Posted by ike84

So I need to go and watch scanner danners videos about cats because my knowledge of them is still very much comic book version. When they fail what is the main symptom? Do they choke down the exhaust and kill power through reduction of flow? Or do they just stop cleaning up the exhaust and result in no other difference? I remember newarts video of how he toasted his cats when he blew his engine but that's the only other time I've ever heard of them going bad.

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Yes, ScannerDanner and also Schrodingers Box on youtube have great videos on fuel trims, O2 sensors, failing cats etc. ScannerDanner is a professional and Schrodingers Box is a DIY guy, so the videos are different, but both focus on the mathematics and science of engine controls.

From what I've learned watching their videos it appears that your former statement is what occurs. The failed cats typically impede the flow and result in very poor engine response and a lot of hot start issues. That said, I see exactly what blue62 was referring to with respect to my downstream O2 sensors. With the car at a steady rpm, a properly functioning cat should result in a downstream O2 sensor with a very flat output. My downstream O2 sensors do not look like they are doing that. Hence, a back-pressure test, to see if the cats are clogged or failing ... or at least that's my understanding from watching ScannerDanner and asking questions of my mechanic buddy.

[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.