Expectable Variance Between Long Term Fuel Trims Banks
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 851
Likes: 103
From: St Louis, MO
Expectable Variance Between Long Term Fuel Trims Banks
I recently replaced my airbox, throttle body and HFC. My scanner shows bank number 1 running at about 10% while bank two is at 4% (this is at idle).
The car is at 13% and 7% while driving. The numbers have decreased as I drive the car over time (100 miles). I have been told the car will keep learning and adjust.
Is it ok to have a 6 to 7% variance between the 2 banks or does it indicate I may have a small leak from my install?
Bank #1 (is that the driver's side)?
The car is at 13% and 7% while driving. The numbers have decreased as I drive the car over time (100 miles). I have been told the car will keep learning and adjust.
Is it ok to have a 6 to 7% variance between the 2 banks or does it indicate I may have a small leak from my install?
Bank #1 (is that the driver's side)?
Pro
Joined: Sep 2018
Posts: 667
Likes: 302
From: Nova Scotia Canada
Did you preplace the gaskets when you did the cats? If not MAYBE there is a leak at one of the flanges. Watch for carbon marks. Maybe an issue with the O2 sensors? What are you seeing at WOT?
If able perhaps have someone with HP Tuners plug in and have a look. That will provide you with much more information.
This is an interesting one. Good luck and please report back with your findings.
This MIGHT help
If able perhaps have someone with HP Tuners plug in and have a look. That will provide you with much more information.
This is an interesting one. Good luck and please report back with your findings.
This MIGHT help
Last edited by Bobbo76; Apr 15, 2025 at 11:03 AM. Reason: video added
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 851
Likes: 103
From: St Louis, MO
Did you preplace the gaskets when you did the cats? If not MAYBE there is a leak at one of the flanges. Watch for carbon marks. Maybe an issue with the O2 sensors? What are you seeing at WOT?
If able perhaps have someone with HP Tuners plug in and have a look. That will provide you with much more information.
This is an interesting one. Good luck and please report back with your findings.
This MIGHT help
https://youtu.be/Rhg5NSh8Dq8
If able perhaps have someone with HP Tuners plug in and have a look. That will provide you with much more information.
This is an interesting one. Good luck and please report back with your findings.
This MIGHT help
https://youtu.be/Rhg5NSh8Dq8
Drifting
Joined: Feb 2023
Posts: 1,361
Likes: 1,125
I recently replaced my airbox, throttle body and HFC. My scanner shows bank number 1 running at about 10% while bank two is at 4% (this is at idle).
The car is at 13% and 7% while driving. The numbers have decreased as I drive the car over time (100 miles). I have been told the car will keep learning and adjust.
Is it ok to have a 6 to 7% variance between the 2 banks or does it indicate I may have a small leak from my install?
Bank #1 (is that the driver's side)?
The car is at 13% and 7% while driving. The numbers have decreased as I drive the car over time (100 miles). I have been told the car will keep learning and adjust.
Is it ok to have a 6 to 7% variance between the 2 banks or does it indicate I may have a small leak from my install?
Bank #1 (is that the driver's side)?
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 851
Likes: 103
From: St Louis, MO
There are many things that ultimately affect your fuel trims. The missing piece of the puzzle is - what your trims were before your component changes. Barring this, my question is: does your airbox change the way air flows across the MAF? If it does, this alters the engine's load calculation and this, in turn, will affect other things. It would be a good idea to double check for an exhaust leak. By itself, your trims are a little discerning, but within the realm of what is acceptable.
I am hoping, after a few more miles, the numbers will come down. I am really concerned bank 1 is too high.
Drifting
Joined: Feb 2023
Posts: 1,361
Likes: 1,125
I am doing a smoke test tomorrow am before I remove any parts. Everything I read says numbers over 10 at each bank could be a problem and the total of the short and long term numbers should be 10 or less.
I am hoping, after a few more miles, the numbers will come down. I am really concerned bank 1 is too high.
I am hoping, after a few more miles, the numbers will come down. I am really concerned bank 1 is too high.
Thread Starter
Burning Brakes
Joined: Jan 2004
Posts: 851
Likes: 103
From: St Louis, MO
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