1.5T Very High Fuel Trim Reading

[sirspazalot]

I drive a 2017 Si recently tuned with TSP stage 1, no other performance mods. I’m seeing some radically low fuel trim readings in bank 2. My Short term and Long term fuel trims for bank 1 fluctuate around 0, never +\- 10%.

However STFTB2 consistently sits at -62% and LTFTB2 at -100%. I’m not sure if this is an error with sensors or is a legit reading. Car doesn’t behave out of the ordinary outside these readings. Any insight?

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[PowerPerLiter]

I drive a 2017 Si recently tuned with TSP stage 1, no other performance mods. I’m seeing some radically low fuel trim readings in bank 2. My Short term and Long term fuel trims for bank 1 fluctuate around 0, never +\- 10%.

However STFTB2 consistently sits at -62% and LTFTB2 at -100%. I’m not sure if this is an error with sensors or is a legit reading. Car doesn’t behave out of the ordinary outside these readings. Any insight?

False reading. There aren't any bank 2 sensors on a 4 cylinder. Bank 1 sensor 1 and bank 1 sensor 2.

Some of the 19 and 20s don't use long term trim either.

 

[PowerPerLiter]

If your seeing strim hovering around zero its pretty much perfect. Probably because your still on the factory intake.

 

[sirspazalot]

False reading. There aren't any bank 2 sensors on a 4 cylinder. Bank 1 sensor 1 and bank 1 sensor 2.

Some of the 19 and all the 20s don't use long term trim either.

That makes sense thank you, good to know the fuel trims are right where they should be.

 

[Si2020]

@PowerPerLiter how do you effectively look at your short term and long term fuel trims? Is it at a given speed is it full throttle? My Ltft is around -7 around town and -4 to-5 ish cruising on the highway. Short terms bounce a bit. I have full bolt ons and race MAF. Thank you for any advice you could give.

 

[Si2020]

I forgot I am on TSP Stage 1

 

[PowerPerLiter]

@PowerPerLiter how do you effectively look at your short term and long term fuel trims? Is it at a given speed is it full throttle? My Ltft is around -7 around town and -4 to-5 ish cruising on the highway. Short terms bounce a bit. I have full bolt ons and race MAF. Thank you for any advice you could give.

They are more or less averaged together. Thus results the long trim number.

Think of it like this... long term trim is a "global" fuel adjustment, meaning, across the board that's the percentage of fuel being added or removed.

Short trim number is the "immediate" or current correction percentage.....

So if long trim is -5, and short trim is +5, then that equals zero. If long trim was 0 at the same point short trim was adding +5 percent, then you would need to add 5 percent to that exact spot for "perfection".

The ecu is doing this the entire drive cycle.

That's why tracking it and making sure not a single spot is that far off makes a big difference.

The car will allow ~37% +/- before alerting the owner....

Imagine if for a split second it needs to add 37% fuel at 6000 rpms on a full bolt on car at 23+ psi..............

 

[Si2020]

I am beginning to understand. Thank you for the info. I guess for the time being, I am ok with a long term of -7-8 and short terms of -3-4. I guess I could benefit from a tune @PowerPerLiter what is the gain of getting a tune hp and torque wise from adding full bolt ons to Tsp stage one? Again I really appreciate your reply.

 

[PowerPerLiter]

The gain really is safety.

Derek did a good job at assessing needed correction for a multitude of vehicles but by design it can't be perfect for all setups.

These computers are wild in the fact that they are excellent at long term self correcting and allow for ALOT of it before seemingly having an "issue" of some sort.

 

[Si2020]

I guess I am safe enough until I get a clutch and run e35. Then it would make more sense to get a tune. I will have Derek do it. I just don’t spend $400 on a tune and realize I need a clutch. Because once I get a clutch I will definitely go ethanol. Thanks again

 

[Gruber]

False reading. There aren't any bank 2 sensors on a 4 cylinder. Bank 1 sensor 1 and bank 1 sensor 2.

Some of the 19 and all the 20s don't use long term trim either.

@PowerPerLiter Could you elaborate on the last sentence?

 

[PowerPerLiter]

@PowerPerLiter Could you elaborate on the last sentence?

There are a increasingly higher amount of cars coming with ecu's that do not use the long trim function of fuel trimming (not monitor-able by our tuning devices etc)

 

[Gruber]

There are a increasingly higher amount of cars coming with ecu's that do not use the long trim function of fuel trimming (not monitor-able by our tuning devices etc)

So something actually changed in MY 2019 and 2020 civics? Fuel trim numbers wouldn't show on the Ktuner for example?
As I understand, the trim numbers for all 10 gen civics from the beginning, are not used for any actual fuel "trimming" but only are calculated to show the deviation between what the ECU actually does, which is based on the O2 sensors, and the MAF-based fuel calculation, which has not been used in closed cycle anyway. So actually, no "trims" were applied from the beginning of 10 gen at least.
But a large deviation ("trim") would indicate that something is broken, and so it would help in diagnostics. So why would Honda remove it maliciously so it's non-monitorable?

 

[PowerPerLiter]

Im a little lost in your interpretation of the fuel trim function and closed loop operation.

The fuel is being adjusted by the percent of the fuel trim function of the ecu. All modern vehicles use fuel trim function and the purpose is to ADJUST FUELING off of the map/maf signal based fuel tables. This really only happens in closed loop. Open loop is when the vehicle is not correcting via fuel trims.

All current 10th gens do this. As to why honda changed the long term trim function for certain ecu's I dont have an answer for. They all still use short trim and I am sure just because we cant monitor long trim with our current tuning solutions honda has kept SOME form of long term fueling adjustment. You have to remember there are many functions our computers do that is not seen. Hondata and ktuner both state there are a myriad of tables we dont ever get access to with these....

 

[Gruber]

Im a little lost in your interpretation of the fuel trim function and closed loop operation.

The fuel is being adjusted by the percent of the fuel trim function of the ecu. All modern vehicles use fuel trim function and the purpose is to ADJUST FUELING off of the map/maf signal based fuel tables. This really only happens in closed loop. Open loop is when the vehicle is not correcting via fuel trims.

All current 10th gens do this. As to why honda changed the long term trim function for certain ecu's I dont have an answer for. They all still use short trim and I am sure just because we cant monitor long trim with our current tuning solutions honda has kept SOME form of long term fueling adjustment. You have to remember there are many functions our computers do that is not seen. Hondata and ktuner both state there are a myriad of tables we dont ever get access to with these....

Actually, it's the other way around at least in this car. The trims are not used for anything in normal closed loop driving. Normal driving fuel supply is solely determined by the O2 sensors. No trims applied. The "trims" are only a calculated deviation between what the actual fuel flow is, and what would be orderd by the PCM if the PCM was using the MAF sensor (but it's not). The STFT was never used for anything except troubleshooting. The LTFT was stored, and then presumably used to trim the MAF based fuel supply, at least for the next cold start (open loop), and maybe for any other instances of open loop operation.

I've heard now for the first time that Honda allegedly decided to hide deeper the LTFT. Maybe now it is not used for anything at all, and the fuel supply in open loop is determined in some other way? Seeing how much the LTFT fluctuates depending on whether I was driving fast or idling much before I parked the car, I would think that using the LTFT from the last drive to trim the fuel supply for the next cold start makes very little sense. So I'm not sure if LTFT was ever used even in the older MYs. Maybe it was never used, so they removed it or hid it deeper.

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