Flex Fuel and Long Term Fuel Trims

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blakebonkofsky
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Flex Fuel and Long Term Fuel Trims

Postby blakebonkofsky » Sun Nov 20, 2016 3:03 pm

I understand how the long term fuel trim setup works, but I'm curious how it reacts when flex fuel is brought into the mix. I know about the composition and scaler tables for the fuel adjustments, but how does the long term trim table affect the main fuel map when not on straight gasoline (if the engine was originally tuned on gasoline). Is the long term table applied to the Fuel Composition Correction map, or is it still applied to the main fuel table? Basically what I'm asking, will the corrections end up fighting each other if the fuels are changed back and forth on a semi-regular basis?

I do see the option for a 3rd axis on the LTT table, locked to Fuel Comp, and I assume it would log to those separate tables when configured, I'm just curious what happens if those maps are configured and I hit the "Apply LTT" button. Is it similar to the situation of V engine with 2 o2 sensors, only applying corrections common to both banks and then leaving the remainder in the LTT table? Say, at 0% ethanol the logged LTT is +8% at a certain cell, and +12% at the same cell at 85% ethanol, would it apply 8% to the main fuel table and leave 4% in the 85% ethanol table when I press the "Apply LTT" button?

Also, is there any baseline map available for Fuel Composition Correction? Something to at least get me close for regular pump fuel vs. E85?

Thanks for any help you can provide to clear the confusion going on in my head right now.

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blakebonkofsky
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Re: Flex Fuel and Long Term Fuel Trims

Postby blakebonkofsky » Sun Nov 20, 2016 5:28 pm

Scratch the question, I've figured it out by manually putting in LTT numbers and applying changes to see what it did. If the fuel table doesn't have the matching 3rd axis, it just dumps the extra tables and only applies the first LTT table to the main fuel table. Having to use a 4D fuel table defeats the purpose of the Fuel Composition Correction table, but I suppose logging those LTT numbers and then manually correcting the FCC table would work as well. It makes sense to do it that way, because if you only ran E85 for a while, if the software applied those numbers to the FCC table, it would be working on the assumption that the primary fuel table is correct, which may not be the case. Then, if you switched back to normal gasoline, it could all go haywire again. In the end, I suppose it won't matter a whole lot, just wanted to get a feel for how it did things. Ideally, the fuel tables would be tuned pretty closely before ever using the LTT anyway.

But still, if anyone has a rough base table for the FCC, that would be very helpful!

Spadam9
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Re: Flex Fuel and Long Term Fuel Trims

Postby Spadam9 » Thu Nov 24, 2016 4:36 pm

I have found using a 4d fuel and LTT table with 0, 25, 50 and 75% ethanol to work well (they both need to be 4d to apply the trims) and don't use the scalar. I also found the automatic Ethanol compensation in the main set up to be about 15% too lean (in my case 15% rich going back to pleb spec dino fuel). So I adjusted the injector scalar value for ethanol percentage (like you would on a stock ECU) to compensate which seemed to work really well. Not sure if this is what haltech intended but it works.

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HaltechMatthew
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Re: Flex Fuel and Long Term Fuel Trims

Postby HaltechMatthew » Wed Dec 14, 2016 8:56 am

It is how I do it too. Base table in 4D vs Composition, and the same for LTT. The scalar itself is used for stoic correction, just dont use the fuel composition correction table.

IMHO it is there for backwards compatibility for those importing previous generation ECU maps or those more familiar with this older method.

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blakebonkofsky
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Re: Flex Fuel and Long Term Fuel Trims

Postby blakebonkofsky » Wed Dec 14, 2016 9:10 am

So you are suggesting simply to use the FCC table to get it close, and then tune the 4D fuel tables? Or not use the FCC table at all and simply have the target lambda FCC table make up the difference? This will be my first time tuning a flex fuel vehicle, I just want to get it right and not have to start over from scratch halfway through because of an initial setup error.

Also, does the target AFR map compensate for ethanol percentage automatically, or is that the purpose of the FCC table under the Lambda section? I would love to see a functional example calibration for a flex fuel equipped engine if you have anything you are willing to share. I think seeing one setup and ready to go would help me understand.

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HaltechMatthew
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Re: Flex Fuel and Long Term Fuel Trims

Postby HaltechMatthew » Wed Dec 14, 2016 9:17 am

By selecting Flex as the fuel type it will already do the stoic correction based off the scalar table. Your 4D mapping over flex fuel composition is only then to fix errors in fuel flow modeilling and tuning differences.

Set to Flex, do not turn on the correction tables, instead map over 4D. It will then learn the table over mulitple compositions and simply get better over time.

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blakebonkofsky
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Re: Flex Fuel and Long Term Fuel Trims

Postby blakebonkofsky » Wed Dec 14, 2016 9:30 am

Gotcha, that makes more sense. So remove both FCC tables (Lambda and Fuel).

Also set the ignition table over 4d as well?

Thanks Matt and Adam(?), you've been a big help!

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HaltechMatthew
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Re: Flex Fuel and Long Term Fuel Trims

Postby HaltechMatthew » Wed Dec 14, 2016 9:33 am

Yeap. You can also 4D the target if you want to vary the AFR with changing fuel composition.

superskaterxes
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Re: Flex Fuel and Long Term Fuel Trims

Postby superskaterxes » Wed Dec 21, 2016 9:20 pm

i have a question regarding this topic, once you put the respective tables into 4D mapping, how does the interpolation work between ethanol percentages? Say i have 0/25/50/75 as my 3rd axis and im running 37.5% ethanol, do the trims split half way between the tables? do all of my 3rd axis's need to be identical for fuel comp?

also, the fuel density scalar is currently set for some percentage of ethanol, but how does this change based on your ethanol content? if there is already a fuel comp scalar why do you need to know the density (assuming this is factored into the scalar already).
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HaltechMatthew
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Re: Flex Fuel and Long Term Fuel Trims

Postby HaltechMatthew » Wed Jan 04, 2017 12:58 pm

Density is for the non-ethanol part of the fuel.

Yes it does interpolate in all dimensions.

Flat_Rate
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Re: Flex Fuel and Long Term Fuel Trims

Postby Flat_Rate » Thu Jan 26, 2017 10:11 am

Good thread, just upgraded from Platinum Pro to Elite, explains alot!!

mantrx7
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Re: Flex Fuel and Long Term Fuel Trims

Postby mantrx7 » Fri Feb 10, 2017 4:20 pm

would be great to see a Hatech Tech video on this. As its quite different to the previous E85 haltech video on how do to the calibration

mantrx7
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Re: Flex Fuel and Long Term Fuel Trims

Postby mantrx7 » Tue Feb 21, 2017 3:17 pm

Gents,

In regards to this.

Does the Fuel Comp scalar still interpolate between the 4D maps via the % factor? or does it a does tit read linearly between the 4D maps (i'm only running a 0% and a 85% currently. Curious how it wants to scale in the intermediate ranges.

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HaltechMatthew
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Re: Flex Fuel and Long Term Fuel Trims

Postby HaltechMatthew » Mon Mar 27, 2017 3:37 pm

Yes it does interpolate in all dimensions, and it uses the scalar.

Unless your flow rates and dead times are absolutely perfect I would add a little more resolution thatn just 0 and 85. I would normally as a minimum go 0,25,50,75 and the same for Long Term. After 75% the difference greatly lessens.

mantrx7
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Re: Flex Fuel and Long Term Fuel Trims

Postby mantrx7 » Wed Apr 05, 2017 2:50 pm

Cool, thanks.

Would still make a good tech video :) I can donate my Rx7 if you want :)


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