Very High Negative Fuel Trims

Lulu733

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Hello everyone, this is my first post. I have a 2017 Honda Civic Si Coupe, with 50k miles. On my Ktuner V2, it’ve noticed my Short term fuel trims(STFT) usually range between -16% to 4%. My Long Term Fuel trims (LTFT) currently sitting at -14% to -10%. I am in college right now, and my driving habits consist of short trips to the gym, Walmart or doordashing (a lot of idling). Whenever I commute home (2.5 hr drive), I can ‘manipulate’ my short trim to make my long term fuel trim reach 0% or -1%. I cleaned my air filter last night and my fuel trims look about the same after going on a drive. I’ve read 27Won’s article on air fuel ratios, but any one have advice on what it could be? Maybe new spark plugs, because I’m running 21-24psi whenever I beat on it. New fuel injectors? Should I drive with rev hang, or keep it off?


Current modifications:
- Ktuner V2
- TSP Stage 1+
- Cobra Cold Air Intake (Street MAF)
- Type R shifter assembly
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Ap1 George

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Hello everyone, this is my first post. I have a 2017 Honda Civic Si Coupe, with 50k miles. On my Ktuner V2, it’ve noticed my Short term fuel trims(STFT) usually range between -16% to 4%. My Long Term Fuel trims (LTFT) currently sitting at -14% to -10%. I am in college right now, and my driving habits consist of short trips to the gym, Walmart or doordashing (a lot of idling). Whenever I commute home (2.5 hr drive), I can ‘manipulate’ my short trim to make my long term fuel trim reach 0% or -1%. I cleaned my air filter last night and my fuel trims look about the same after going on a drive. I’ve read 27Won’s article on air fuel ratios, but any one have advice on what it could be? Maybe new spark plugs, because I’m running 21-24psi whenever I beat on it. New fuel injectors? Should I drive with rev hang, or keep it off?


Current modifications:
- Ktuner V2
- TSP Stage 1+
- Cobra Cold Air Intake (Street MAF)
- Type R shifter assembly
Seems fine, mine also runs a little on the richer side and would do anywhere from -1 to -1x and I'm running a custom tune from one of the top tuners for this platform. I only track STFT because that is the "now", I believe LTFT is an average over time
 
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Lulu733

Lulu733

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Lulu733

Lulu733

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Seems fine, mine also runs a little on the richer side and would do anywhere from -1 to -1x and I'm running a custom tune from one of the top tuners for this platform. I only track STFT because that is the "now", I believe LTFT is an average over time
Glad to know it’s not uncommon, I just get paranoid and want to make sure this car lasts at least 200k miles.
 


ValkenDnB

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That’s an excellent article, really enjoyed reading it. I’m going to go through the list of possible culprits for high negative integers.
Tbh it might just be a dirty air filter. You have the cobra and it sits so close to the floor. I see it all the time when people post their cobras for sale on here.
 
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Lulu733

Lulu733

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Tbh it might just be a dirty air filter. You have the cobra and it sits so close to the floor. I see it all the time when people post their cobras for sale on here.
Possibly, I actually thoroughly cleaned it last night and let it dry the entire night. I went on a drive and it's about the same.
 

Neddih

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I think it is important to factor in how the car is actually running while you are driving it, I have the 27Won RACE MAF and even with a custom tune by Drob. My LTFT does almost exactly what you have described, idle and short drives make it look rich because there isnt enough load but long trips bring it back down. Since then I have stopped tracking fuel trims as an early indicator, if something feels off with the car is when I will monitor again
 
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Lulu733

Lulu733

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I think it is important to factor in how the car is actually running while you are driving it, I have the 27Won RACE MAF and even with a custom tune by Drob. My LTFT does almost exactly what you have described, idle and short drives make it look rich because there isnt enough load but long trips bring it back down. Since then I have stopped tracking fuel trims as an early indicator, if something feels off with the car is when I will monitor again
Yeah, I think I'm going to remove STFT and LTFT from my Ktuner's layout. Sometimes, I do have rough starts though, but I think that might have to do with spark plugs and needing to get new ones.
 

gtman

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You should run datalogs from time to time to check out trims though. Don't forget to add your car to the community tuning thread. Link is in my signature.
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