Fuel Trim help needed, please advise

[kwhiteside]

Hey Guys, I ditched my FAST92 and started over with stock tune. Been thru AutoVE and AutoMAF ( both table and maf tuning with LTFTrims disabled ) car idles great, commanded afr following actual, less than 1 degree knock at up to 120mph.

Set all parms back to normal so VE and MAF and Fuel Trims and DFCO are all running again. Now my LTFuelTrims are between 15 and 20 most the time. Heading to track Saturday and need to whip this tune into shape.

Should I do some more AUTOMAF runs with the Fuel Trims left on this time or what?

[kwhiteside]

Found a post by Mr Prick about some calc_pids and added them. I was already logging LTFT's so they show up. I created a couple maps using his new LTFT Ben and LTFT Avg PID's as shown below. This was a very freeway type cruise home mostly idling along, so not real valuable.

Seems to me that the AVG map is saying the LTFT are having to add a bunch of fuel all the time.

The FT Ben map seems to be saying I need to paste and multiply to b0101 to bring in more fuel, most cells around the 1.2 multiplier range.

Few questions

When I went thru AutoVE speed density mode I had b0101 with .01, why the digression???

b0101 isn't going to be my key factor at the track as I'll be running over 4k rpm and foot in the pedal coming out of turns. Wont I be running MAF most the time?

Thanks in advance, Ken . . .

[kwhiteside]

Seems I did my AutoVE in open loop and never went back thru the VE part after going back to closed loop with the LTFT enabled. I see now that I have to do that.

[mr.prick]

Those LTFTs are high, if everything is configured right and
you don't have an intake or exhaust leak it is probably because
you tuned in OL then re-enabled LTFTs.

Tuning in OL makes the VE lower than it would be in CL.
Having gone thru the whole AutoVE thing and not understanding why
AFR was always lean at cold start and when IAT got above 95°F or
rich when ECT and IAT dropped after the engine warmed up, I bought a RR.

With the RR I could see how much higher cold start VE values would be then gradually go down as ECT got higher,
sometimes they got very low, lower than my minimum limit.
They where never a constant reliable value in OL always up and down
to get that perfect 1.00 BEN.

After OL tuning and re-enabling LTFTs I also noticed cold start was still lean
and LTFTs would be quite high.
I then decided try using LTFTs and WBO2 for VE tuning, this richened cold start AFR and got VE value to where LTFTs would be in the magical 5% to -5% range, no more positive LTFTs at WOT and as a bonus VE was smooth.

IMO
OLSD is good for getting a general shape of the VE.
Once this is done add X% to VE and then use LTFTs.

[kwhiteside]

I do have a question in general.

Looking at the same log file

Map Wideband BEN says I should barely up the fuel
Map LTFT Ben says multipley by 1.20 in most cases.

I can see how doing the LTFT tuning will no doubt reduce the need for the fuel trims to help out, but wont adding all that fuel to the VE table cause my actual AFR to no longer follow commanded?

Seems like two evils competing. I need actual following commanded, but I also want those fuel trims down to zero. How is that going to happen?

[mr.prick]

That's because LTFTs are keeping AFR near stoich.
You will still be near stoich after making changes with it (LTFTBEN),
AFR will not be affected too much in CL.
AT cold start you will be richer.

In CL the NBO2s keep AFR to what {B3601} is set to,
if LTFTs are highly positive before PE you will get LTFTs during PE.
This will usually make you rich.
When they are 0 in PE AFR will be close to commanded provided
VE is proper in those areas.

It will work if you use the filters,
don't change the same cell(s) with both BENs.