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Flex fuel on G4 (non plus)

Link G4 Plus Software Tutorial

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Im about to start playign with flex fuel on the G4+ and the older G4.

Am i correct in thinking that you can only have a "overall" 2d correction to IGN/Fuel with the G4? ie. Can not tune cell by cell?

Ok I had more of a play and came it with some kind of solution. Not sure its its the best way to do it though?!

Something like below?

With the G4 there is no dedicated flex fuel functionality so you need to create a work around using the overlay tables as you have figured out. This does mean that you don't have a dedicated E85 ign/fuel map to tune and then a blend between the two like you can with the G4+ or most ECUs using a dedicated flex fuel strategy. Instead you are making changes to your normal pump gas map based on ethanol content.

I'll ask another one of our members to post in here with a description of how he is using the G4 for flex fuel as I know he is achieving really good results.

Thanks Andre,

Hi guys, sorry it's taken a bit to reply - I don't seem to get many opportunities to ramble as much about this kind of stuff as I like to.

When Andre mentioned this thread it made me ponder on it and realise I haven't ACTUALLY done any flex tuning with a G4 Link in years, I guess that kinda means that while I don't feel there is a way of doing as well as I'd like it and there is always a compromise - it is strictly speaking livable, at least the way I did it. I'd not say that it's the best way, but it seems to have done the job so far.

I'm actually going off memory here, but things that more or less come to mind which may be worth thinking about or playing with... I hope I remember this right:

- The style of maps you have done there are what I initially started with but actually probably are excessive and complicated, probably not necessary and to a degree may actually be better to just keep with 1 overlay where possible. I *think* I ended up with ethanol content vs load for fuel and ethanol content versus rpm for ignition, though I *may* have done a 5d table for load to pull back a bit of timing at higher boost on lower ethanol percentages where knock may have come into it.

- I used 80% ethanol as my base map and adjusted from there, at the time I did it (not sure if this has changed) the 4d/5d fuel tables had a maximum %age trim you could specify in them. My memory is a bit hazy here, but from memory the trim is "add or subtract x%" of whatever the current value is, so if the limit was 30% and you were running a tune with petrol and you needed to add 40% for E85 you are somewhat screwed.

The way one can get around that if that (still?) applies is lets say the fuel table value needed for E85 is "100" and the value needed for petrol at the same point is "71.4" and your base map is on petrol then you need a "+40%" number in your 4d table which if there was a 30% limit is not viable. The trick here is though is that if you have E85 as your main table you "only" need to subtract 28.6% from 100 to hit 71.4. Though I could be completely off, this was AGES ago but that's kinda how I remember it, I've not had the chance to go back and look.

- Cranking enrichment: E85 needs HEAPS more fuel than petrol for cranking. I created a dual fuel table set up as an overlay table as it has (or had?) much bigger limits for values than the 4d/5d tables did and I found I needed big cranking enrichment to get nice starts. From memory I had the dual fuel overlay table on so long as the engine was under 400rpm, and as it happens it never seems to dip that low in normal running so that works well - though you should need no extra trims really over 40c ECT or so.

- I think may have done something similar for the lower temp warm up enrichment stuff too, with a 5d table - when you are dealing with different amounts of fuel and compounds that have different evaporative properties things like this and accel enrichment aren't going to scale perfectly. I just did as much due diligence as possible and hoped the end compromise wasn't noticable and it seems like I've got away with it, but would MUCH prefer to have something like a G4+/Haltech/something else if I had to do it again.

Those are the main thoughts that come to mind, hope that helps in some way - happy to try and answer anything if you have any questions.


Thanks a lot for the time, Fantastic answer! Thanks i will have a go!! if not I will look at a g4+!

The logic you mention sounds perfect!


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