e85 AFR with openflash

[nickw14]

So I've been doing a little bit of research on the stoichiometric ratios for different fuel types. This research was prompted by a high LTFT (about 20% to be exact). It appears as though the stoich ratio for e85 is 9.7:1 vs the 14.7:1 of regular gas. Looking at the OFT tune for e85, it looks like it tries to maintain a "14.7-like" afr (which would mean a reasonable afr in open loop and closed loop based on the stoich ratio for gas, if that makes any sense).

Would it be a good idea to adjust the AFR for the stoich ratio for e85? I really don't want to mess with the vendor tune on the OFT because it functions very well, but I also am concerned about fuel trims/ongoing problems... Here is a picture of the open loop AFR table and the closed loop adjustment tables.

[Illuminaughty]

High LTFT at what RPM/Load? I think it's a bit cleaner to leave the fueling the same (stoich being 14.7) and change the GDI Pressure, injector scaling, crank pulse widths, and probably some more but it's late and I'm on my phone. I'd compare the differences between the OFT E85 and OFT 93 tune to get a feel of what needs to be changed. I agree though, the OTS tunes are very solid.

[504]

To my understanding, the ECU reads lambda from the oxygen sensor not actual air to fuel ratio strictly.

If the oxygen sensor in the exhaust stream detects excess oxygen it is running lean and reads a lambda >1 which translates to an air to fuel number > 14.7 which we are all familiar with.

That 14.7:1 you are seeing is just a reference for lambda = 1 = stoichiometric ratio for whatever fuel the car is burning even though it actually is burning at 9.7:1.


Hope that clears things up!

[steve99]

Originally Posted by nickw14

So I've been doing a little bit of research on the stoichiometric ratios for different fuel types. This research was prompted by a high LTFT (about 20% to be exact). It appears as though the stoich ratio for e85 is 9.7:1 vs the 14.7:1 of regular gas. Looking at the OFT tune for e85, it looks like it tries to maintain a "14.7-like" afr (which would mean a reasonable afr in open loop and closed loop based on the stoich ratio for gas, if that makes any sense).

Would it be a good idea to adjust the AFR for the stoich ratio for e85? I really don't want to mess with the vendor tune on the OFT because it functions very well, but I also am concerned about fuel trims/ongoing problems... Here is a picture of the open loop AFR table and the closed loop adjustment tables.

As previous poster,s said, the o2 sensor does not know your running e85, the Ecu firmware is set up for petrol so it reads petrol AFR. So 14.7 is Stoic. wether its petrol or e85 , if your fuel trims are that high you have intake or exhaust leak or an aftermarket intake and MAF sensor is not calibrated or your running wrong fuel for tune. problem with maf or o2 sensor ect.

LTFT is the ecu,s attempt to get the afr the ecu is asking for ie the OL Fuel table value (or cl depemding on fueling mode) to equal the afr measured by the 02 sensor.

If their is a constant discrepency the ecu attempts to correct this with ltft.

[nickw14]

Originally Posted by 504

To my understanding, the ECU reads lambda from the oxygen sensor not actual air to fuel ratio strictly.

If the oxygen sensor in the exhaust stream detects excess oxygen it is running lean and reads a lambda >1 which translates to an air to fuel number > 14.7 which we are all familiar with.

That 14.7:1 you are seeing is just a reference for lambda = 1 = stoichiometric ratio for whatever fuel the car is burning even though it actually is burning at 9.7:1.


Hope that clears things up!

This makes sense, thanks. However, the measured AFR during datalogging still reads close to 14.7:1 at idle. If this is fine, then great. Otherwise, I guess I still think there's a "problem" if you want to call it that.

Originally Posted by steve99

As previous poster,s said, the o2 sensor does not know your running e85, the Ecu firmware is set up for petrol so it reads petrol AFR. So 14.7 is Stoic. wether its petrol or e85 , if your fuel trims are that high you have intake or exhaust leak or an aftermarket intake and MAF sensor is not calibrated or your running wrong fuel for tune. problem with maf or o2 sensor ect.

Agreed. And the tune supposedly uses the fuel trims to account for e% changes. I have been meaning to re-calibrate my MAF sensor, which will probably fix the LTFT spike.

LTFT is the ecu,s attempt to get the afr the ecu is asking for ie the OL Fuel table value (or cl depemding on fueling mode) to equal the afr measured by the 02 sensor.

If their is a constant discrepency the ecu attempts to correct this with ltft.

This is a great explanation for LTFT. Thanks.

[Kodename47]

Originally Posted by nickw14

This makes sense, thanks. However, the measured AFR during datalogging still reads close to 14.7:1 at idle. If this is fine, then great. Otherwise, I guess I still think there's a "problem" if you want to call it that.

Your O2 sensor is reading Lambda 1, not 14.7:1 AFR. The standard setup for the OFT is just petrol AFR scale. You could correct that for E85 by doing:
(AFR/14.7)x9.7 = E85 AFR

[aagun]

ok

the ecu work at PATROL PLATFORM THAT IS NEED 14.7 cm3/air to burn 1 cm3/fuel and that is = 1.0 Lambda (14.7/14.7 = 1 )

if we let the ecu work at E85 PLATFORM THAT IS NEED 9.7 cm3/air to burn 1 cm3/fuel and that is 1.52 Lambda (14.7/9.7 = 1.52)

the ecu think he is going to lean and try add fuel until he got 1.0 Lambda so STFT will set @ 30% - 35% (14.7/14.7 - 9.7/14.7 = 1 - 0.66 = 0.34*100 = 34% ) more fuel to make lambda = 1 to be sure = 1.52 - (1.52 * 34%) =1.52 - 0.52 = 1 lambda

a 30% LTFT WILL used at OL MODE AND MAKE IT WORSE

fa20 ecu is made to read PATROL PLATFORM only . so we need to add 30% - 35% more fuel at E85 PLATFORM to make the ecu happy . = 1 lambda

TUNERS fix high LTFT by ADDing 30% 35% of fuel to the main table to let the LTFT near 0% + advancing the spark BTDC

TUNERS USE lambda ONLY because it will be = 1 at all type of fuel and make it easy to calibrate fuel tables .


see blow

[steve99]

The fueling in oft tunes is adjusted for E85 by chahanging the Injector Scaling Brz parameter about 30% to correct port injection fueling and adjusting the GDI Pressure mutiliplier by 30% to correct the direct injecton fueling.

your fuel trims on E85 will move arround a bit due varing e% but should be less than 10% if maf scaling is ok ie intake not changed.

you should not need to adjust injector scaling or gdi pressure multiplier or even fuel tables.

its easier to correct maf scaling on petrol but can be done on e85 if you have a consiestent mix, varing e% will throw off maf scaling calcs, best to scale for average e%in your area.

[aagun]