Changing LTFT's via "Airflow vs Output Freqen

[NCal]

Are there any detrimental affects from richening closed loop A/F ratio using Airflow vs Output Freq. rather than rescaling the IFR's?

I ask because in a previous tune, the guy seems to have used the AFvsOF table to bring my LTFT's from the +7% range to the -6% range, then a few weeks later the car read excessively rich on the Dyno. I was wondering if the 2 things might be related ???.

Nick

[NCal]

Anyone?

[Chris@HPTuners]

well it kinda achieves the same thing although the MAF table is modifying airflow and the IFR table is modifying fuel.

increasing the MAF table tells the PCM more air is coming in which means it adds more fuel.

similarly, decreasing the IFR table tells the PCM the injectors are smaller than they actually are, which again means it adds more fuel.

most people mod the iFR table cos it doesn't mess with your timing and other airflow and g/cyl based values. Although if i had to bet as to which of the MAF or IFR tables is likely innacurate i would say the MAF.

[NCal]

Chris, I understand that. Here's my situation. The last time I had the car Dyno'ed (after receiving that tune) the A/F showed 11.9:1 on the wideband. Before that tune I could get my A/F to 12.8:1 (w/Predator) via the PE adjustment. But after the new tune (and 9 months later), leaning out my PE by 5% had no effect on my overall AFR (still 11.9:1). I was wondering if by changing the AFvsOF rather than the IFR (to get my LTFT's in the minus range), they could have caused an overly rich condition that couldn't be addressed via the PE adjustment.

If that's true, I'll remove that tune, reinstall the stock tune and achieve -LTFT's via IFR scaling only (leaving the AFvsOF values stock). If not, then I need to look for other causes that aren't tune related (COT, lazy O2 sensors, etc..). Right now I'm using the Predator tune and fine tuning IT with HPT for -LTFT's (@ cruise) and 0 KR.

Should I just start from scratch with the original tune? Am I creating a Frankenstein monster by starting with the Predator tune? My car is an '01 CamaroSS, M6, K&N FIPKII, SLPP D/D Cat-back, TB coolant bypass & a Greddy Catch Can (to keep oil out of the intake). Dynojet #'s 334rwhp/356rwtq Corrected


BTW, where would I look to see if COT is causing this problem and if so, what should I do to keep it from interfering with my overall A/F ratio?
TIA. Nick

[Chris@HPTuners]

it sounds like COT to me, take a look under Engine -> General, you will se the COT master enable/disable and also the COT temp thresholds. Either the master disable or increasing the temps will disable it.

also, check your openloop F/A table, it will override the PE table if it is greater than the PE value.

[NCal]

Thanks Chris . I'll check those tonight. And since you didn't say that the AFvsOF changes are harmful, I'll leave them alone.

Maybe I'll write another tune using only the IFR to fix the LTFT's and do a comparison on the Dyno. I'll be sure to post the results.

Thanks again for your timely response.

Nick

[NCal]

it sounds like COT to me, take a look under Engine -> General, you will se the COT master enable/disable and also the COT temp thresholds. Either the master disable or increasing the temps will disable it.

also, check your openloop F/A table, it will override the PE table if it is greater than the PE value.

OK, so in the PE table (above 800rpm), the values are all 1.146. So it would be Stoich, or 14.628/1.146=12.76:1 A/F ratio for PE.

In Openloop F/A vs ECT, all ECT's >140*F = 1.13 or higher. So that would be 14.628/1.13 = 12.94:1 A/F ratio for OL F/A........

.. meaning that the PCM will choose the PE Table since it generates the richest mixture (w/COT turned off).

Am I figuring this correctly? Or am I just plain lost?

Nick

PS: I'll be sure to turn COT off during the next Dyno session to eliminate that as a fuel adder.

[jimmyblue]

I think COT is "busier" than most people realize. I set
my max COT enrichment to 1.05 and min to 1.01, and
if I log the F/A multiplier on normal driving I often see
these numbers (which are pretty unique to COT) come
and go with almost any "happy foot" at all. Sneaky and
persistent.

[NCal]

Hey jimmyblue, how's it going? This is the problem you were helping me with (on LS1.com) a couple months back. Actually, I'm still running the same tune (using HPT to fine tune things) since my O2's gradually dropped from 940mv to the 890-900mv range. I just haven't been able to get back on the Dyno to verify things. I figure since it delivered good hp/tq increases even with the 11.9:1 AFR it was worth disecting . I'm currently mapping all my old Custom Tunes to learn how they went about things .

So are you saying that you're seeing COT show up during "spirited" everyday driving? If that's the case, how can we (ie..those running Cat-Cons) expect to set up a stable A/F ratio with the COT wildcard showing up randomly?

Also (concerning my previous post), am I understanding the dynamics correctly, or am I off base?

Nick

[jimmyblue]

I reduced my max COT enrichment to 1.05, to minimize
its effect on tune. Which might or might not leave any
"protection".

The way you have the "choosing of enrichment value"
is how I understand things. For whatever that's worth.

[NCal]

I reduced my max COT enrichment to 1.05, to minimize
its effect on tune. Which might or might not leave any
"protection".

The way you have the "choosing of enrichment value"
is how I understand things. For whatever that's worth.

Cool, I wanted to make sure I'm on the right track. I'm going to leave my COT #'s alone for now (fear being the big motivator here :-/ ) and just shut it off at the Dyno or Track. If my WOT O2#'s start looking fat, I'll alter the COT values then start tracking the F/A multiplier to see how much of a problem it is with my car. Thanks.

Nick

[jimmyblue]

One thing you might want to do, is check the COT
min and max enrichment values and log the fuel/
air multiplier when you drive, and if you see these
values pop up instead of 1.0 and {whatever your
PE/OLFA values are} that's a big red COT flag.

I don't recall whether COT is additive to the base fuel
calc or just another choice that supersedes the base
if richer. I have to go find that post about fueling and
look at it again.

[Chris@HPTuners]

COT overrides if richer.

[jimmyblue]

OK... so if you just keep readjusting your COT max to
be no greater than the max(PE, OLFA) as you tune,
then COT will not be whacking you out, just a little less
effective in "quenching" the cats (but probably still
enough to let them live).

[Chris@HPTuners]

i have COT disabled totally on my own car, been like that for 2.5 years, over 200 dyno runs, makes around 470 fwhp @ 12.8 AFR / 6500 RPM.

Cats haven't melted yet ;D

[NCal]

Alright, since my PE value of 1.146 represents the PCM's mixture of choice (not counting COT), setting the COT MAX value at 1.138 should be invisible to the PCM during WOT. 8) Ill do that.

Chris, I've been re-reading your statement from your first post:

"most people mod the iFR table cos it doesn't mess with your timing and other airflow and g/cyl based values. Although if i had to bet as to which of the MAF or IFR tables is likely innacurate i would say the MAF"

how does modifying the AFvsOF mess with timing or other g/cyl based values? FWIW, the Tuner guy chose the new AFvsOF values w/out the benefit of data logs so I wouldn't call the changes "specific" to my application. That being the case, could this tune be reducing VCM efficiency by adding so many variables that WOT becomes inconsistent? In other words, would there be less residual affect by achieving -LTFT's exclusively through IFR scaling?

Nick

[Chris@HPTuners]

well a whole bunch of things use the calculated g/cyl value for reference, the most obvious is spark timing.

If you increase your MAF table then you will move downwards in the spark table (usually lower numbers). You just need to be aware of this, by logging using the histograms.

[NCal]

Ok got it. Thank You Chris .