Weird P0171 Code
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Teching In
Joined: Sep 2021
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Weird P0171 Code I've been having trouble tracking down the source of an apparent vacuum leak on bank 1 of my LY6 and would like to leverage the collective knowledge this forum has to offer. First, a little background.
The motor is a 6.0L LY6 2009 from a 2500HD with a 6L90 swapped into a 1972 Starcraft motorhome.
EVAP was removed and plugged.
Throttle body was replaced
New O2 sensors
Symptoms:
At idle my LTFT is running at 19.5 on B1, B2 running around 2.3
STFT are cycling between + and - with activity similar between banks.
As I raise the RPM, right at 2500 rpm, I can hear a slight single click sound and the B1 LTFT drops instantly to around 2.3, Its like the source of the vacuum leak closes when the vacuum drops to a specific level.
When I pull the O2 sensors, B1 looks to have slight carbon coloring compared to B2. Exhaust manifold leak??
I've tried a few methods to find a vacuum leak (propane, carb cleaner) with no luck. SoI'm thinking if it is a vacuum leak, it must be on the valley side of the intake. And before I remove it (which I really, really don't want to do), I'm hoping someone has a definitive answer.
The motor is a 6.0L LY6 2009 from a 2500HD with a 6L90 swapped into a 1972 Starcraft motorhome.
EVAP was removed and plugged.
Throttle body was replaced
New O2 sensors
Symptoms:
At idle my LTFT is running at 19.5 on B1, B2 running around 2.3
STFT are cycling between + and - with activity similar between banks.
As I raise the RPM, right at 2500 rpm, I can hear a slight single click sound and the B1 LTFT drops instantly to around 2.3, Its like the source of the vacuum leak closes when the vacuum drops to a specific level.
When I pull the O2 sensors, B1 looks to have slight carbon coloring compared to B2. Exhaust manifold leak??
I've tried a few methods to find a vacuum leak (propane, carb cleaner) with no luck. SoI'm thinking if it is a vacuum leak, it must be on the valley side of the intake. And before I remove it (which I really, really don't want to do), I'm hoping someone has a definitive answer.
TECH Addict
Joined: Oct 2016
Posts: 2,513
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From: PDX-OR-USA
What was used to plug the un-needed evap connections? I've found its deceptively hard to find good vacuum fitting caps. The average ones bake out and get hard then crack. The fancy colored rubber ones tend to get soft and loose, a quality tie wrap can fix those up. (like a mini hose clamp) I buy them from real electrical supplier. and ask for heat rated ones.
TECH Apprentice
Joined: Oct 2016
Posts: 321
Likes: 30
From: Massachusetts
I've been having trouble tracking down the source of an apparent vacuum leak on bank 1 of my LY6 and would like to leverage the collective knowledge this forum has to offer. First, a little background.
The motor is a 6.0L LY6 2009 from a 2500HD with a 6L90 swapped into a 1972 Starcraft motorhome.
EVAP was removed and plugged.
Throttle body was replaced
New O2 sensors
Symptoms:
At idle my LTFT is running at 19.5 on B1, B2 running around 2.3
STFT are cycling between + and - with activity similar between banks.
As I raise the RPM, right at 2500 rpm, I can hear a slight single click sound and the B1 LTFT drops instantly to around 2.3, Its like the source of the vacuum leak closes when the vacuum drops to a specific level.
When I pull the O2 sensors, B1 looks to have slight carbon coloring compared to B2. Exhaust manifold leak??
I've tried a few methods to find a vacuum leak (propane, carb cleaner) with no luck. SoI'm thinking if it is a vacuum leak, it must be on the valley side of the intake. And before I remove it (which I really, really don't want to do), I'm hoping someone has a definitive answer.
The motor is a 6.0L LY6 2009 from a 2500HD with a 6L90 swapped into a 1972 Starcraft motorhome.
EVAP was removed and plugged.
Throttle body was replaced
New O2 sensors
Symptoms:
At idle my LTFT is running at 19.5 on B1, B2 running around 2.3
STFT are cycling between + and - with activity similar between banks.
As I raise the RPM, right at 2500 rpm, I can hear a slight single click sound and the B1 LTFT drops instantly to around 2.3, Its like the source of the vacuum leak closes when the vacuum drops to a specific level.
When I pull the O2 sensors, B1 looks to have slight carbon coloring compared to B2. Exhaust manifold leak??
I've tried a few methods to find a vacuum leak (propane, carb cleaner) with no luck. SoI'm thinking if it is a vacuum leak, it must be on the valley side of the intake. And before I remove it (which I really, really don't want to do), I'm hoping someone has a definitive answer.
But aside from that, have you tried to
1. change the intake manifold gaskets? I doubt it to be the cause, but if you suspect it's coming from the intake valley side of the intake......
2. is the engine tuned right? I also doubt this to be the case, but a badly tuned engine will throw a lean code. Mine did and it just threw it on one bank. I'm guessing you're using the factory pcm? Same tranny as the engine's donor vehicle? I will tell you that I was losing my mind tracing a vacuum leak after I installed a procharger complete kit. The tune they sent me was way off. The car was running like it had a vacuum leak.
3. Like Wannafbody said, Check the pcv system.
4. Spray some soapy water to see if you have an exhaust manifold leak.
5. Maybe you have a clog in the fuel rail on that side or one or two dirty injectors not shooting enough fuel. THAT CLICK YOU HEAR CAN BE THE SOUND OF A FUEL INJECTOR FINALLY WORKING.
Last edited by 2001ws6ft; Sep 13, 2021 at 12:18 AM.
Thread Starter
Teching In
Joined: Sep 2021
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Thanks everybody for your ideas. I think I've finally have things sorted out. It was MULITPLE problems!!
1. I rechecked all vacuum lines and found a V shaped crack in the vacuum line to the evap valve. It acted like a flap and when vacuum was high, it would be sucked in and seal. Why it didn't have a bigger impact bank 2 LTFT is a bit of a mystery.
2. I found and re-welded a hole where I welded the bung for the O2 sensor.
3. A ticking sound developed though that I didn't hear before and I was sure it was a lifter! Scanned the oil pressure and it was low (10psi at hot idle). I had just installed a front sump pan so I pulled it back off and checked the pickup tube... The bend in the tube just before the pump was touching one of the windage tray studs preventing the O-Ring from sealing properly on the opposite side of the hold down bolt. Dremel made quick work of the stud and I ordered a saddle so I can bolt down both sides to the pump.
Again thanks to all!
1. I rechecked all vacuum lines and found a V shaped crack in the vacuum line to the evap valve. It acted like a flap and when vacuum was high, it would be sucked in and seal. Why it didn't have a bigger impact bank 2 LTFT is a bit of a mystery.
2. I found and re-welded a hole where I welded the bung for the O2 sensor.
3. A ticking sound developed though that I didn't hear before and I was sure it was a lifter! Scanned the oil pressure and it was low (10psi at hot idle). I had just installed a front sump pan so I pulled it back off and checked the pickup tube... The bend in the tube just before the pump was touching one of the windage tray studs preventing the O-Ring from sealing properly on the opposite side of the hold down bolt. Dremel made quick work of the stud and I ordered a saddle so I can bolt down both sides to the pump.
Again thanks to all!
