need some help with high fuel trims

[Sharkey]

im going to do some work on it today before i do that. i got thinking last night that im going to need to straighten out my ve table before i go further. i know most people dont touch the ve table much, however being mine has been screwed with im going to get the ve error figured out and ill go from there.

ill post a log this afternoon. forgot to save the log from last night and lost it.

[Sharkey]

so i went out and straightened up the ve table, its a lot better in cruise, medium throttle (out of pe), but its still showing error on the rich side of things under deceleration. after i got that mostly squared away i turned the maf back on and retuned cruise and medium throttle with stft, took a couple tried to get that squared up. car feels a lot better now, pulls harder than ever, much smoother at cruise and transitional throttle, quicker throttle response, so far im quite happy (and getting more confidant/less scared with hp tuners).

ive got a log and my tune. a couple things to note, in the fuel tab ive got the gas (gear), gas (p/n) and ivt gain tables zeroed. ive read a couple how to things on both ve tuning and maf tuning that says to zero them while tuning, thats what ive done. dfco is also off, maf is enabled. at one point in the log the afr under boost kinda went stupid, i think it may have been because i was trying to see if 65% boost in 1st gear allowed traction (it didnt lol). every other pull was smooth in the afr department. despite the ve table still being out under decel, fuel trims show slightly rich

have a look, lemme know what you think

[cobaltssoverbooster]

have not tried this myself. but i might have to look into doing this when i put on the 60s.

so you make a histo with the inj fr vs kpa vac and log fuel trims on it??

i used to tune cup cars for POC and the idea behind that came from my experience with tuning the porsche 928 series. the base fuel table in a porsche 928 stays the same when i tune for different fuel injectors. by calibrating the injectors perfectly in the kpa injector setting your more or less fine-tuning the flow rate at every perspective kpa value, thus being more precise on afr and bringing the trims closer to 0.
from what i saw in my last file it was working the same way. i had the maf disabled to start and when it was pretty close on the injector kpa settings i re-engaged and calibrated maf. done

[Sharkey]

thats interesting, and makes sense. really with my car i changed the injector tables and i went from having 25% + error under deceleration on my ve table constantly (see error, make changes, have the same error, getting nowhere), changed the injector settings and then had -25% error till i got the table where it should have been, then everything seemed normal.

anyone had a chance to look at my tune/log? ive made a couple minor maf calibration changes since then, nothing serious. fuel trims seem to have settled in the 0 to -4 range, ive got a couple (under decel) around -6 or -7. need a little more work there, stink i still have some error in the ve table. i however popped an o2 sensor code today so going to change it before i do anything more.

[GM COBALT SC SS]

i used to tune cup cars for POC and the idea behind that came from my experience with tuning the porsche 928 series. the base fuel table in a porsche 928 stays the same when i tune for different fuel injectors. by calibrating the injectors perfectly in the kpa injector setting your more or less fine-tuning the flow rate at every perspective kpa value, thus being more precise on afr and bringing the trims closer to 0.
from what i saw in my last file it was working the same way. i had the maf disabled to start and when it was pretty close on the injector kpa settings i re-engaged and calibrated maf. done

so this is sort of a way to fine tune the injector flow rate values, correct? like if you did not receive a flow sheet with the injectors? as i said im putting on 60s and have read that they actually flow anywhere between 60-65 lb/hr. i could use this method that your talking about to fine tune them as close as possible since i do not know the actual value? and then redo maf and ve to get airflow close to perfect??

sorry to thread jack sharkey

[cobaltssoverbooster]

yea that was the idea....it worked that way with the 928's so i used it again lol.

i would start with the standard 60's setup and go from there. if it works for you let us know.

[GM COBALT SC SS]

ill do that man. especially since they i did not receive a flow sheet for it.. when i get around to it. lol
i just hope they are flowmatched as advertised. id expect if they were off, then such fine tuning might not be possible

[Speedytec]

Hmmm, I have similar problems with my VE table. I did numerous logs to dial in the VE table (trims for cruising stuff etc. WB AFR% error for PE tuning) and I keep getting a strange big hump in the lowest decelleration range (15, 21 & 28KPa)

Whatever I do, my fuel trims say I need much more fuel in that VE area. (DFCO is disabled but that still seem to kick in: AFR =>~20. Press the clutch in on any decelleration part. Filter the logs for any AFR above 16-17...)

I suspect this is injector(-setting) related. Have 42lb Lucas fitted on a return style set-up. Will upgrade soon to #60 Siemens and use the injector parameters from the spreadsheet.

My MAF curve dials in fine and no problems there.
Any ideas on the VE hump?

[Sharkey]

like i said, i changed my injector settings, it brought the ve table back to what it looked like stock, worked out the maf calibration and its back in check. i find it odd cause i had this issue with both 42lb and 60lb injectors. my original tune with the 42s was supposed to be a gm stage 2 tune.

id assume injector parameters are going to be a little different for a return style system.

[Speedytec]

Return style should make injector settings pretty simple. The flow rate vs KPa is a straight line, as the pressure differential over the injectors is constant. At least that is what it should be, but thinking of it I should test if it's still linear at those very low manifold pressures during decelleration...
Can this VE hump be related to puls adder and min pulse width settings?

[GM COBALT SC SS]

sharkey, do you have dfco turned on or off when you are tuning??

i just ask because i havent actually turned mine off in tuning until today and i realized that it was affecting my fuel trims. it was causing the only lean spot on the whole histo at like 10-20 %

prior to today i always ran dfco on and i think thats what caused the lean spike and that may be your problem which causes such crazy spikes in the ve table. i think in dfco the fuel trims 0 out.

maybe someone can confirm this.
and if you need dfco off, i think you could maybe filter out any values when injector pulse widths are zero. not totally sure but i read that somewhere

[Sharkey]

ive been tuning with dfco off. as far as i know, dfco wont affect the ltft, however the fuel trims are being learned before dfco kicks on. however as far as logging afr error with dfco on, im sure it will show huge error.

[GM COBALT SC SS]

well i know that when i was logging yesterday with dfco off for the first time, i was seeing lean spikes that werent there before. and i also do know that it would affect afr error and thats why i dont use afr for anything other than pe mode.

but i watched my ltft + stft histo creep from -2% up to 20% by 2 to 3 % intervals as i was decelerating with dfco off. and the wideband was also creeping from 14.7 to 16.00 which is its max at the same time. im gonna try it again with dfco on again and see if i get the same results

edit: i dont watch just ltft's however, i watch ltft + stft in the same histo, so if ltft are disabled and stft are still enabled then maybe thats why im seeing the spike with dfco off.

[Sharkey]

when i log afr error i disable ltft learning. im not sure if this is correct, however the way i see it if the computer is learning ltft and correcting while im trying to log to correct the table, it seems counter-productive, and i dont really get anywhere.

i was seeing the same thing as you were with my old tune and dfco off. wideband going to max (20.9 in my case), fuel trims climbing till it went past 18% and set a p0171 code. with the new injector settings in the same scenario, because my ve table was set rich trying to correct the old tune, my wideband went rich, around 12:1, and my fuel trims were falling like a rock. i disabled fuel trim learning, logged afr error for ve, did that a couple times with tweaking it and it sorted out. re-tweak the maf table and it seems good.

[GM COBALT SC SS]

hopefully someone will correct me if im wrong, but i understand fuel trims as the percentage of fuel that gets added to the mixture to keep stoich. so you can use that percentage just like afr error in tuning maf and ve. then you dont have to disable the fuel trim learning and can tune in closed loop. it saves alot of time and can be much easier. well at least it does for me.

but i understand the way you do it too. in open loop right? but i am thinking you would no longer have an issue with the lean spikes your seeing if you tune the fuel trims in closed loop with dfco on as opposed to afr in open loop with dfco off.

[GM COBALT SC SS]

just realized that my idea about dfco causing issues is completely stupid. for some reason i was thinking if you tuned with it off, then it would affect how the car rides when it is enabled again. but that cant be right

[Sharkey]

when dfco comes on fuel trims are not updated. dfco doesnt come on right away when you lift your foot, fuel trims under decel get updated, then dfco comes on. in the case of what was happening with my car before was it was tuned lean under decel, however it wasnt affecting anything. during that second between lifting the throttle and dfco coming on the fuel trims would work their way up trying to correct the lean condition. when dfco is on, fuel trims dont update, however if your in a trim cell, your in that cell and it will set p0171 despite the fact that its in fuel cut.

[GM COBALT SC SS]

yeah, that all makes sense. thanks for the explanation. how is the tuning going now??