Mitsubishi EvoX - Stopping the fuel trims affecting WOT fueling PDF Print E-mail
Stopping the fuel trims affecting WOT fueling

Ok we all know how the Fuel Trims work, basically MAFHz bins, so Low/Medium/High

Usually High isn't used, here is why:

Left is stock, Right is my modified one

So the High FT won't be used unless the MAFHz goes above 1593.75, which won't really happen on stock turbo.

So I have modified the High bin so it's lower. And thus gets used.

Now here's the best part, because of how the STFT works, the High FT should really NEVER get populated with anything OTHER than 0%.

I have done a log and you can see the High FT being used in the fueling calculations, and you can also see it being set to 0%, so now I don't have my Cruise (Med) Trim affecting WOT.


Low -> Mid
Mid -> Low
Mid -> High
High -> Mid

That's for 53040010, but also should work for 526800XX - If your values for above don't look very similar to mine then something's wrong.

If your interested in logging trims then find the MUT_TABLE - then you have the addresses you need to log:

MUT0C = LTFT_Low (Usually Idle)
MUT0D = LTFT_Medium (Usual Cruise)
MUT0E = LTFT_High (Usually not used, but that's what this MOD is all about)
MUT50 = Copy of the trim currently in affect

find the MUT_TABLE - then you have the addresses you need:

You should be able to see the trim being used by logging MUT50 - same formula as the other trims...

1) There are many addresses
2) Evoscan requires a prefix of "23"
3) Depending on whether you are requesting an ODD or EVEN byte you will need to say returnbytes=1 or 2.

You can log MAFHz with MUT1A (x*6.25) and then you should be able to see when the STFT drops to 0% (closed loop)

MUT50 guys... that is the copy of the current LTFT in affect...
and when I say log MUT50 - I mean grab the 4 bytes @ MUT50 (0x0080XXYY) and log that (0x0080XXYY)

it wont zero out the trims. it will force the high trim to be used, which should be zero

did you try logging MUT50? you can see it transition from low -> mid -> high (it will be the same %'s anyways)

I found that the mid trim varied so much that the stock setup really wasn't ideal. So "disabling" it seemed like the best option. So far my WOT AFR's have been much more predictable.

I settled on 343/350, since this is about 140-160 load (at 2500rpm) .

I had my WOT AFR's at about 11.5-7 and then with this change they went terribly lean to about 12.5's. I was just wonder if it was me or no. Ofcourse knock showed up. So I had to redo my entire AFR map.

Chris - Log the memory address of MUT1A - that's MAFHz, formula is x*6.25

Thanks tephra for figuring this out! You're a genius!

I have some mixed feelings about disabling LTFT from affecting WOT. On the one hand, it's great to not have this extra factor affecting things. On the other hand, it's possible that the weather compensations don't make up for the cold weather enough, and that without LTFT, AFR's can get too lean as Hiboost experienced when the weather is cold.

The concept of LTFT affecting WOT makes sense - if in closed loop, the car can't achieve the right stoich afr, it will adjust fueling based on a learned percentage to keep AFR's correct despite any long-term issues such as seasonal changes, clogged air filter, fuel differences etc. However, as we have seen, LTFT can vary WAY too much in a single day. It needs to be more stable in order for it to work properly when used to adjust WOT.

One specific concern is that in most areas, they add more ethanol to standard fuel over the winter. I believe (or maybe just blindly hope) that LTFT would adjust for this and keep AFR's safe. My main concern is that without the LTFT affecting WOT, I will need to more closely monitor AFR's. Note that I have a wideband but it is not permanently installed. Anyone else have any experiences with disabling LTFT in WOT? I guess it's hard to say because who knows what will happen to AFR's (without LTFT) in the summer when it heats up again.

the ECU should still be doing temp/baro compensations on the fueling.

No matter what your high oct or low oct fuel maps say, your ECU will always try to achieve 14.7 while in closed loop. You cannot adjust your AFR in closed loop unless you put some sort of resistor in between the O2 sensor and the ECU, making the ECU think it's at 14.7 when it actually isn't. The only other way to adjust your AFR at idle is to go full open loop by zeroing out your open loop maps like mentioned above.

Actually there is a constant Front_02_Voltage_0.5V = 0x1A => 0.01952*26 = 0.50752V in ECU one could tweak, but I cannot see the reason to do it.

Last Updated on Sunday, 18 July 2010 07:16
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