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Fuel vs Gear

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I noticed that usually on higher gears we have richer afr, so, to reach target afr, we need to remove some percents by gear-fuel trim. Question is, how much you trimming from your experience, and what determines this effect?

Below is not best, but very illustrative example.

Is this from a road session or a dyno?

It could be any matter of trims kicking in, intake air temp for one, also is it hitting the same load sites on the map? In the lower gears your through them quickly, once into the higher gears the ecu has more of a chance to control the fuel properly

Hello Chris, thanks for you answer. It is from road run. All fuel trims are 0 in this session. Same load sites also, but yes, fifth gear is much longer then fourth, but if I run car on the dyno at 4th gear with ramp rate so, that I run from 5500 to 9000 rpm about 8 seconds - I have afr very close to target, but on road at 5th gear CLL lambda decrese fuel by 15-18% to reach target afr.

Also what EGT you prefer at so high gear and 2,7 bar of boost on gtx42 size turbocharger if probe is installed just in 1 inch from head port?

I've not encountered anything like that, but looking at the fact that your MAP looks to be if anything higher but your IDC looks lower there seems to be a very substantial difference in either:

a) How the engine is breathing

b) How the fuel system is working

c) How accurate the O2 sensor reading is reading

I guess strictly speaking your IAT has increased enough to need some trim but off-hand needing 17% less fuel at 38degC versus 20ish seems a bit excessive - HOWEVER it looks like CLL is actually targetting half a point leaner than what it has stabilised at in 3rd and 4th so between the IAT trim not being sorted and the fact that your are running about 4% leaner in 5th when CLL catches up that does make things a certain amount less drastric.

I also think the fact that you have done the last gear change almost several hundred earlier than what appears to be your normal shift point has resulted in the data for 5th being for a rev range which barely overlaps with the earlier data as well which makes it an extra variable to deal with when looking at that data. Not really convinced that'd be causing what we can see there, but hooking 5th 500rpm or so later would probably make the start of the 5th gear sample more relevant.

Those are my thoughts from a first look over it anyway, no great bits of wisdom there or anything but I figured I'd mention that bunch in case that adds a different perspective to what you are looking at and helps further ideas :)

Good luck and let us know how you go

It's not uncommon to see a slight variation in AFR between gears. What you will often see is the AFR is a little leaner in perhaps 1st/2nd gear. In the taller gears though where the engine is under moderate/heavy load you should see reasonably consistent AFR. There are a couple of points to note:

1. The log for 3rd and 4th gear which are the only two that are really directly comparable under the same rpm range and boost pressure are very close in AFR. It looks like your CL trim is pulling perhaps an additional 2% (ish) out at high rpm in 4th but if you're not utilising an IAT trim table then this would be a factor as to why that's necessary.

2. As Lith mentions, you change in to 5th gear and end up in an rpm range you don't see in the other gears so it is possible that the main fuel table needs some work here. You only just start getting into the same rpm range as we saw for the other gears right at the end of the log file. At this point your closed loop trim is -17% which on its own is excessive in light of the only factor you've logged - IAT (that alone I would expect to see a trim of around -5% between 20 deg C and 38 deg C IAT). However at 6500-7000 rpm in each of the other gears you also see a rich dip in the AFR trace. I can't form a specific answer but based on what I can see I'm suspecting that you may be a little rich in the fuel table below about 7000 rpm. In the lower gears this isn't too obvious as you pull through that rpm so quickly. In 5th however you start well below this rpm and pull through it much more slowly.

That's about all I can add based on the data you've got. A full log of 4th gear from perhaps 3000 rpm or a short shift from 3rd into 4th to show this same low rpm area of the tune might show some valuable data. Often when you're flat shifting on the road or track the turbo speed is maintained meaning you end up in an area of the mapping that you can't actually get to on the dyno (low rpm but high boost).

Thanks alot Guys, I will try to work more with this car and I will let you know results.

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