I have a 2.25 exhaust and a SRI with a heatshield, but the Fit feels the same, and I've discovered through here that the factory ECU supposedly rewrites itself back to a stock parameter for fuel economy. In the shop I have an Auto-Tech class in, we have a Snap-On Modis tool that can read/write on the factory ECU. I was hoping someone could help me, to tune my fuel trim/map to fit my modifications to compliment them. Any advice helps. Or anything about the Modis, if it truly can rewrite the factory fuel trim or if it can't, or if the computer will re-learn over that too. Any bit helps.

 

i do not beleive you can re-write the ecu with that snap-on tool. if that was the case, performance shops woudl not be using AEM FIC, flashpro, hondata, etc. to tune cars.

the way the stock ecu works is to always target 14.7 a/f ratio. short term fuel trim (stft) and long term fuel trim (ltft) are adjustments the ecu makes to reach the target a/f.
if adding your intake and exhaust leans out the engine to 15.0 a/f...the ecu will richen up the stft (and over time the ltft will follow) in order to get back to 14.7 a/f. this doens not mean that you will loose your gains made by the added parts, because they will still be allowing the engine to flow bettter.
with that said, a tuen will help to smooth out and make the most out of the powerband, but the small gains you see from intake/exhaust will not be greatly effected by your fuel trims.

 

^ word

and typically, the ecu doesn't adjust timing/fuel towards a fuel economy goal, but towards desired torque as written from factory... so when we install i/e's the computer will tone things as close to factory as it can, not that i/e's won't still do anything, but the computer does try to compensate to stay as close as it can to the factory desired torque...

 

Could you expand on this for me. I'm trying to understand what might effect the fuel trims I see in my 2010 stock Fit. What means the 'factory desired torque'?

 

Sometimes certain scan tools have the ability to tweak a few parameters but really without being there to see/feel changes as we go through, unless you have a data log to share and a list of what (if any) changes the tool can make it's really hard to say.

You cannot directly change the FT's you have to modify other bits and then those swing your FT's

So for instance at idle if you do something like change stuff like the fuel type, ISC position, injector dead time or the base fuel pressure this would mess with your fuel trims.

What I would aim to do is, first find out what effect on timing, airflow and lambda your modifications have had.

Then you could go in with a plan.

For example, lets say you added a less restrictive intake and exhaust.. did you pickup airflow but the ECU didn't like that so it cut your timing and enriched the mixture?

That is where you compare what the ECU wants to do in both closed and open loop on the maps to the numbers it actually lets you run.

This is where FT's come in, how much did the ECU have to adjust fuel input?

Well there was more Load (air mass) so the ECU adds fuel, but at the same time it doesn't want to damage its' self so it adds yet more fuel than necessary to slow the reaction, in addition to pulling timing to yield a safer combustion.

Without a actual numbers from your Lambda/AFRs, Timing advance and Airflow it is tough to recommend any changes. This all depends on whether that particular scan tool can make any meaningful tweaks as well. A few can, the vast majority can only pull data.

 

I allready saw somewhere that certain Nissans could be adjusted for regular or premium fuel via a scantool.... but i don't remember where i saw that, if that was a joke or what models......

Marko!

 

It is true of the VQ35DE and VQ37DE, I would wager a few more as well but those are the scan tools that require a >$1k license for operation on top of the cost of the scanner. So only a dealer or a brand specific tuning shop would likely have one of those.

They can re-adjust the timing among other bits via the OBD2 port on the G35/37's and the 350/370Z's

 

i'll try...

keep in mind that all of this applies in closed loop (normal driving)


fuel trims will only be a small part of the equation for what the ecu is doing to adjust things as close to stock as it can... and it gets even more complicated with the electric throttle...

so if the engine is "flowing" more air (from an i/e point of view) the engine will adjust the ltft and either base spark, or spark adjust to tone back the effects of the i/e over time... it could also change the throttle angle, injector pulse width, etc...

also, i'm not SURE if this is the case with the fits, but the "desired torque" is a manager of sorts to determine what many parameters are doing inside the ecu... basically, if the fit is written with different desired torque numbers at different rpm/throttle positions (called cells), it will adjust all the parameters it needs to in order get as close to those predetermined numbers as it can...

so if, at 50% and 4k rpm, the desired torque is 75 (i don't even know if that is the type of input it sees) and you have installed a i/h/e and it's seeing more than that, it can slightly close the throttle plate, richen up the mix, pull timing, etc so that it tries to get as close to that predetermined number as possible...


technically the computer can only do so much... if the head was ported, valves oversized, longer duration/higher lift cams, larger tb, intake, header, exhaust were all installed (aside from a number of issues that will probably come up) the computer will most likely not be able to scale things back enough to act like stock, and a long-term gain will be had...

which is why a "tune" is so important... even to a stock car...


dunno if this makes sense... trying to do my best

 

I feel like if you did all those modifications you would be so far out of the factory ecus learning parameter the car would barley run if at all and no gains would be had agreed tune is most important

 

Thanks aplex and dsm. To throw a wrench into the discussion, my butt 'feels' a better response when running premium fuel. There's been a ton of discussion regarding this 'phenomena' - though I am beginning to understand it's truth. What conclusion might be drawn regarding the Fit's ecu. I'm trying to keep to a stock set-up, it's what I have and am trying to understand.

 

I've noticed that while driving the Fit feels "dead" on normal take off and sluggish, even with the throttle wide open. But, if I drop from 3rd into second and then slam the throttle to the floor, at about 3k RPM's, it shoots forward like it actually makes torque.

I've started wondering if the problem isn't in ECU tuning or lack of power, but if the Fit just simply isn't open enough at the throttle body (Or the throttle response curve limiting take-off) and exhaust.

 

check it out and give me your input it could change everything https://www.fitfreak.net/forums/2nd-gen-ge8-specific-fit-engine-modifications-motor-swaps-ecu-tuning-sub-forum/68251-has-anyone-tryied-bypassing-eld-must-see-might-change-everything.html