2012 Mustang GT stumbling at part throttle

Rypper1

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I have a 2012 Mustang GT that has developed a pretty heavy stumble at part throttle. It doesn't seem to do it at WOT, if it is I don't feel it. It developed in the last week or so. The only mods are Pypes LTH, High Flow catted H pipe, and a Lund tune. I have reloaded the tune, completed an idle relearn, found I had lost one of the bolts at the collector on the headers and replaced it. Datalog is showing 0 AFR on bank 2. That is not on a WOT pull, just driving around a bit. I haven't contacted Lund yet since it is the weekend. I was hoping someone here could point me in the right direction or at least give me some things to check.

Thanks
Randy
 

Rypper1

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I also meant to ask, where does the afr reading come from with SCT X4? I went back and looked as some of my old datalogs and bank 2 afr was reading in those.
 

Rypper1

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Yes, I have cleaned both a couple of months ago. Cleaned the MAF again today.

I could have sworn I put this in chit chat.
 
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skaarlaj

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I too have Pypes headers, and I also had one of my O2 sensors go out, but there was no stumbling at part throttle for me. Mine threw a code 2195 I think. The passenger's side afr reading 0 for you seems like a pretty good clue though. Btw mine was the passenger's side also.
 

redfirepearlgt

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^^^ Agreed. 0 is not a good reading as idle should indicate Lambda 1.0 give or take at idle. First verify your datalog monitoring PID selections. You can verify commanded Lambda against actual by observing PID Lambse bank 2 with measured afr bank 2. They should be close. Compare bank 1 to bank 2. You can also look at short term trims and see how close they are to one another. An erratic Short term on bank 2 compared to bank 1 would be a tell tale.

You may wish to check the integrity of your wiring before replacing the O2 sensor. If extensions were used check them as well. More than once people have found wiring chaffed and shorting to the frame or broken wires within the circuit. A low cost test for this would be to swap the sensors physical locations (don't forget to unplug and swap the connections as well or you will create other issues). If the problem follows the sensor you know the sensor is an issue. If the problem remains with bank two you have a wiring issue or something creating an improper input feedback to the PCM. Good luck.
 
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Rypper1

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You can also look at short term trims and see how close they are to one another. An erratic Short term on bank 2 compared to bank 1 would be a tell tale.
That is the part I really don't get. Short term fuel trim reading between the two banks are pretty damn close. To me that makes no sense. Does the pcm command a fuel input based on maf flow if it is not getting an afr reading?
 

Rypper1

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I too have Pypes headers, and I also had one of my O2 sensors go out, but there was no stumbling at part throttle for me. Mine threw a code 2195 I think. The passenger's side afr reading 0 for you seems like a pretty good clue though. Btw mine was the passenger's side also.

Isn't Bank 2 the driver's side? And if yours wasn't stumbling it makes me think a bad o2 isn't what is causing that. Dammit.

Update: Just rechecked for codes and I have a P0155, bad heater element Bank 2 Sensor 1. Looks like that sensor may be shot after all. New one should be in this week.
 
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redfirepearlgt

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That is the part I really don't get. Short term fuel trim reading between the two banks are pretty damn close. To me that makes no sense. Does the pcm command a fuel input based on maf flow if it is not getting an afr reading?

Agreed. The fact that you are reading 0 on bank 2 yet showing similar ST trims between bank 1 and 2 is peculiar.

The PCM will correct and add or remove fuel (assuming a fixed MAF signal and Throttle position) based on the O2 sensor feedback (which is your AFR bank 2 PID) to maintain LAMBSE command (the calculated AFR being targeted for that bank). There is a lot more to it than that but this is the down and dirty so to speak.

Again before we waste days theorizing why, if, how, when, and so forth, it would be best to swap the O2 sensors and see if the data problem follows the sensor or stays with bank 2. Since that is the obvious here it needs to be addressed first.
 

redfirepearlgt

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Isn't Bank 2 the driver's side? And if yours wasn't stumbling it makes me think a bad o2 isn't what is causing that. Dammit.

Update: Just rechecked for codes and I have a P0155, bad heater element Bank 2 Sensor 1. Looks like that sensor may be shot after all. New one should be in this week.

Therefore the PCM is not going into closed loop mode. The heater on the O2 sensor for bank two is not working. If the O2 sensor never reaches proper operating temp or does not reach it in a specific time frame this code will pop up. May well explain the 0 value on bank 2 though trims are similar.

So again swap the two sensors (or feel free to spend the money on a sensor) and determine if the problem is the sensor or a wiring issue. Guys running LT's run into wiring issues do to having to add relocation extensions or rerouting wiring to accomodate teh O2 sensor location which is now further back of the original O2 position.
 
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Rypper1

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Therefore the PCM is not going into closed loop mode. The heater on the O2 sensor for bank two is not working. If the O2 sensor never reaches proper operating temp or does not reach it in a specific time frame this code will pop up. May well explain the 0 value on bank 2 though trims are similar.

So again swap the two sensors (or feel free to spend the money on a sensor) and determine if the problem is the sensor or a wiring issue. Guys running LT's run into wiring issues do to having to add relocation extensions or rerouting wiring to accomodate teh O2 sensor location which is now further back of the original O2 position.

I do not have extensions on the car. The wiring was pulled from the tabs at the top of the transmission to allow the wire to be long enough to reach. I am going to try swapping the sensors but it will have to wait until tomorrow. Where do the sensors plug in to the harness? I don't have a lift and haven't been able to spot the other end of the wires. Gonna get it up on jack stands tomorrow and get them swapped. Thanks for all your help!
 

redfirepearlgt

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I do not have extensions on the car. The wiring was pulled from the tabs at the top of the transmission to allow the wire to be long enough to reach. I am going to try swapping the sensors but it will have to wait until tomorrow. Where do the sensors plug in to the harness? I don't have a lift and haven't been able to spot the other end of the wires. Gonna get it up on jack stands tomorrow and get them swapped. Thanks for all your help!

that is good news. The location of the O2 sensor bung on Pypes LT's is just on the forward side of the collector flange. The O2 sensor will have a 12-18 inch pig tail. You will have to trace that back to the connector which will be accessible only from underneath the car. Jack stands or safer yet a nice set of ramps should get you the clearance you need to get up underneath and trace the wiring. Not knowing exactly how the installer routed them makes it a tracing job of following the O2 sensor cable back to the connector. If teh problem follows the sensor you have a licked. If the problem remains on bank two its time to start chasing wiring. Best of luck.
 
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Rypper1

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that is good news. The location of the O2 sensor bung on Pypes LT's is just on the forward side of the collector flange. The O2 sensor will have a 12-18 inch pig tail. You will have to trace that back to the connector which will be accessible only from underneath the car. Jack stands or safer yet a nice set of ramps should get you the clearance you need to get up underneath and trace the wiring. Not knowing exactly how the installer routed them makes it a tracing job of following the O2 sensor cable back to the connector. If teh problem follows the sensor you have a licked. If the problem remains on bank two its time to start chasing wiring. Best of luck.

I will have to get it up on jack stands in the morning. I ran it up on a set of ramps this evening but still can't get under the car. The ramps I have are too short to be of much use. Hopefully the problem will chase the sensor when I make the swap. That will be my best out. Thanks again for your help!

Edit: I can see the 02 sensors but I can't get under far enough to see the other end of the pig tail. That is why I was asking about where they were located. I am pretty sure I will be able to see them once I get the car higher.
 
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2011/5.0

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I will have to get it up on jack stands in the morning. I ran it up on a set of ramps this evening but still can't get under the car. The ramps I have are too short to be of much use. Hopefully the problem will chase the sensor when I make the swap. That will be my best out. Thanks again for your help!

Edit: I can see the 02 sensors but I can't get under far enough to see the other end of the pig tail. That is why I was asking about where they were located. I am pretty sure I will be able to see them once I get the car higher.
Their about 8 inches up the side if trans
I just unclipped pass side to replace,drivers side routed above shift linkage
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2011/5.0

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There's a tab you push down on the female side that is on the main harness that releases the sensor
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Rypper1

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Cool, thanks for the pics! I was hoping it wouldn't be a major ordeal to reach up to them, I know there isn't a lot of room to spare on these cars.
 

skaarlaj

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With my car on jack-stands, I had to drop down the rear of my transmission to reach the plug for my front O2 sensors, rediculous imo. I'd hate to see what a Ford dealership charges for the work because of the connectors being on the top/side of the transmission, at least on an auto Coyote car.
 

travelers

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With my car on jack-stands, I had to drop down the rear of my transmission to reach the plug for my front O2 sensors, rediculous imo. I'd hate to see what a Ford dealership charges for the work because of the connectors being on the top/side of the transmission, at least on an auto Coyote car.

It's the same for a stick car too. After I installed the ARHs I had to go with a F150 O2 sensor for the left side because the lead is longer and no longer need the extension that wouldn't stay connected.
 

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