Adjusting LTFT/STFT???
Thread Starter
Instructor
Joined: Jan 2020
Posts: 143
Likes: 12
From: Beaumont, Southeast Texas
Adjusting LTFT/STFT???
6 weeks ago I removed the stock exhaust from my 2015 Z51 and installed new LT headers and used catted x-pipe. The car ran poorly and I replaced leaking header gaskets and changed rear oxygen sensors. Since then I checked a lot of things including the plugs which are okay. I’m showing two codes 2096 bank 1 fuel trim lean and 2099 bank 2 fuel trim rich. Where do I go from here? I can turn off the rear oxygen sensors. Does the tune need adjustment? Or put in new cats? The car was running fine before this change.
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
The leak would cause that same code . Is it active or was it in history
Is it possible you could have switched the leads on the O2 sensors
Rear 02 sesnors have nothing to do with performance as they only monitor cat efficiency
Dave
Is it possible you could have switched the leads on the O2 sensors
Rear 02 sesnors have nothing to do with performance as they only monitor cat efficiency
Dave
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
I have mine rear right O2 harness to right sensor and Left rear harness to left rear sensor... but that would not cause your issues but they should not be crossed
Is your car still running bad after you fixed your leak .. then you either still have a leak or something is wrong with your front O2 sensors
You did not mix up front and rear O2 sensors/ harnesses did u ?
Just putting headers on the car will not cause it to run bad , plenty of guys running around with headers and no tune
I had the connecter come apart on my front O2 sensor ... you sure you have them plugged in right
Dave
Is your car still running bad after you fixed your leak .. then you either still have a leak or something is wrong with your front O2 sensors
You did not mix up front and rear O2 sensors/ harnesses did u ?
Just putting headers on the car will not cause it to run bad , plenty of guys running around with headers and no tune
I had the connecter come apart on my front O2 sensor ... you sure you have them plugged in right
Dave
Last edited by Dcasole; Mar 15, 2020 at 05:34 PM.
Thread Starter
Instructor
Joined: Jan 2020
Posts: 143
Likes: 12
From: Beaumont, Southeast Texas
Finally Fixed
I thought I’d post the final outcome of my efforts since you guys were kind enough to give advice. There were three things that caused problems. First, cracked the spark plug insulators and stubborn me wouldn’t admit it. Second, particular header gaskets had rivets and I installed them wrong which caused air leaks. I ended up using GM gaskets Third, rear O2 sensors wouldn’t play nice with the aftermarket cats so I had them turned off. Once I fixed those three things she runs better than new.
Shout out to Dave, thanks!
Shout out to Dave, thanks!
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
I thought I’d post the final outcome of my efforts since you guys were kind enough to give advice. There were three things that caused problems. First, cracked the spark plug insulators and stubborn me wouldn’t admit it. Second, particular header gaskets had rivets and I installed them wrong which caused air leaks. I ended up using GM gaskets Third, rear O2 sensors wouldn’t play nice with the aftermarket cats so I had them turned off. Once I fixed those three things she runs better than new.
Shout out to Dave, thanks!
Shout out to Dave, thanks!
Dave
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Melting Slicks
Joined: Feb 2007
Posts: 3,297
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From: Raleigh Suburbs
like in the scan above 
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
Dave ....
Melting Slicks
Joined: Feb 2007
Posts: 3,297
Likes: 398
From: Raleigh Suburbs
Le Mans Master
Joined: Oct 2014
Posts: 8,673
Likes: 2,728
From: Atlanta GA
This is all good info but the OP is not asking any questions about tuning .. and pretty confident he does not have or understand HP Tuners .
he popped a code for lean and was asking questions as to why which were clearly answered and he is now running fine ....
Dave
he popped a code for lean and was asking questions as to why which were clearly answered and he is now running fine ....
Dave
Melting Slicks
Joined: Feb 2007
Posts: 3,297
Likes: 398
From: Raleigh Suburbs
Safety Car
Joined: Mar 2004
Posts: 4,048
Likes: 1,478
From: South Florida
While that may be the case I'm just demonstrating where LTFT's and STFT's come into play within HP Tuners, during the scanning, street or dyno same, when you go WOT, they cancel and you are relying on your PE tuning NOT fuel trims any more, until you are off the gas...this you can see as the trims are zero across the board [from the arrow]
In OEM tunes, LTFT's are considered when you go into PE and only STFTs are ignored.The only way LTFT's are ignored in PE mode is if they were specifically tuned that way.
Melting Slicks
Joined: Feb 2007
Posts: 3,297
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From: Raleigh Suburbs