yukio

When swapping to larger injectors, assuming everything else is the same in the engine.
Can i just decrease the fuel table the same % as the new injectors is bigger?
Lets say i am swapping out my 28.8 with 36lb/hr can i then just retract 20% from the whole fuel table as a starting reference point?

Thanks

joecar

Yes... but won't it be easier to set the IFR table to the correct flowrates for the new injectors...?

And, you should also copy the other injector tables (voltage correction, small pulse adjust, minumum pulse...) so the PCM can correctly model the injectors to accurately deliver fuel.

RedHardSupra

iTrader: (1)

doing things correctly is such a drag. it makes things too simple, as it allows the ECU to actually do its job, and let all the predictive and corrective mechanisms assumptions to be successfully applicable. when things go awry, numbers that the ECU spit out can actually indicate the nature of the underlying problem leading to a quick and straightforward solution. all the safeguards and sanity checks actually work with you and not against you. you can reason about changes based on absolute numbers, instead of making purely directional guesses of the 'need more X' variety.

ho would ever want any of these?!

on the other hand, you have the art of changing **** to arbitrarily picked numbers. since it's just a bunch of numbers being added or multiplied, just change all multipliers to 1, all adders to 0, and just tune the entire car with a single variable. who needs the full control of the ECU and the ability to account for various conditions. don't live in the past, tune for the right here, and the right now! you never intended to drive your car in different weather or different elevation anyway. you control the source, quality, and the chemical makeup of petrol you put in your car. the car obviously does not age and the parts don't wear. adjustability is a stupid invention of the hairsplitters. besides, in order to do any of this stuff, you needed to actually pass algebra. math is hard, let's go to the mall!

turbolx

I knew I liked this guy. You tell 'em Marcin!

kenp

iTrader: (9)

That's not what you want to do. The oem injectors are rated at 58 lbs line pressure and the 36 lb injectors you're talking about may or may not be rated at 58 lbs line pressure. Most aftermarket stuff is rated at 42 lbs line pressure.

There are excel tables around on the tuner forums that let you plug in the numbers for your injectors and line pressure and will give you the injector flow rate to input. You'll stall have to adjust small pulse and probably injector offset.

It does get a little complicated at times but there are people around on the tuning forums that will help you.

joecar

lol, this is what makes it so funny, to juggle the tables around requires advanced math vs simply pasting the correct values.

thunderstruck507

iTrader: (18)

Ok guys, so when I replaced my stock 28# with some GM supercharged Buick injectors I looked and they were rated either 41 or 41.5 # at 58psi so I used the Excel table to correct the IFR table.

I did do some minor tweaking to the VE table to make some small corrections, nothing major.

Where can I find more detailed information on tuning the other tables you guys have mentioned and is it something I should be majorly concerned about since the car seems to run great.


The only ongoing issue I have with the car is that often on the first cold start of the day it wants to surge and die at stops no matter the engine temp. But if I turn the car off 15-20 seconds and restart the car it will drive like a dream the rest of the day.

turbolx

Algebra is not "advanced math". Anything they teach in middle school or the first year of high school is not advanced. Differential equations, matrix algebra, and Calc III are advanced. Fortunately, I haven't had to use much of these in most calibration work.

ZL1Killa

iTrader: (17)

You can get those 36# injectors or even 42# injectors and change the IFR table and you will need to tune the VE and likely not notice anything else needing to be changed. HOWEVER, for proper operation the short pulse adder and associated tables should be modified with proper data, as what can happen at low throttle and idle is very large variances in LTFTs & etc with improper data and you tune back and forth around your ***. That also being said going from the 28# to 32# or 36# or 42# with a 5.7L I never noticed the need for all of this data, I scaled the IFR and went on my way tuning the VE, I think I had information (basic) on the minimum pulsewidth and linear range and used those values to change some tables, but I was no where near involved in data as I am now.

The issue arises when you have a large injector (and I don't know the threshold and I'm sure it changes per every engine size) and a low airflow at idle and low rpm.

different types of injectors operate faster or slower and etc...so knowledge about the design and operation need to be known. basically the manufacturer of the injector could tell you a lot, but they are busy mass producing and spitting out injectors or other products, do they have a basic representation of the injector data, yes. And this would tell you minimum pulse width and some other odds and ends. Would this give you the offset table and short pulse adder tables....no. Characterizing injectors is another business as ASNU and others have made it a point to show.


very true, and often enough some of the same problems can be solved without the need for the complex upper math.

joecar

Yes I understand you (you left out vectors, tensors, ring theory)...

the average person who graduated high school considers algebra to be advanced, do they not...?

my point was that it is simpler for the end user to obtain the correct data rather than scale a bunch of tables (the context being 36 lb/hr injectors, so no table is being maxed out here).

turbolx

Mercifully, the BSME program usually tops out at Diffy-Q and Matrices before they turn us loose on Heat Transfer, Fluid Dynamics, and Combustion Theory.

This is exactly what I've been preaching for years while other "schools" have been charging people to teach them bad math. I don't think it's any secret that I've been a HUGE proponent of getting the right injector data before you even start the engine to begin calibration.

DSteck

iTrader: (4)

Yea, if I took it in 7th grade, it's not advanced math. Lol.

I'll admit, I've done polynomial regression to refit data to new labels though.

I sure hope not, but it would explain why society as a whole is crumbling.

I minored in math with my BSME. What a waste of time that was.

Old Geezer

iTrader: (3)

"Algebra is not "advanced math"."............It is for some.

joecar

Greg,
lol, ODE/PDE were a lot of fun, mentally stretching a person in all directions.

DSteck,
I've used interpolation/extrapolation to refit data to new labels, I believe this is ok since you're simply filling in the in-between values, you're not changing the characteristic curve/slope of the data.
Yes society appears to be crumbling, Art majors outnumber everyone else combined.
Maybe you don't use your Math minor in your work, but it has mentally conditioned you to think differently.


So back to the topic, why do people want to intentionally use the wrong injector data (other than scaling to step around some limit)...? This leads to the corollary: why do people tune the WOT AFR by manipulating the IFR table...?

edcmat-l1

iTrader: (10)

I know my gozintas!!










(2 gozinta 4 2 times, 4 gozinta 8 2 times LOL)

Sarg

iTrader: (6)

At what point is an injector too large (or the car flowing too much air) to tune within the limits within the 1999-2000 fbody ecu. I remember something in Gregs video refering to a hard limit in the ecu that needs to be worked around. We have the same thing with the older 16 bit Subaru ecus. There was a g/s limit of 300 that could not be exceeded.

SSpdDmon

iTrader: (10)

MAF is limited to 512g/s. I forget where the line is drawn for injectors. Custom OS's make room for 2 and 3 bar maps. So, the factory ECM is actually pretty versatile. I would suggest once you start making serious power (800+), it might just make more sense to go to an aftermarket system. Sure, you might be able to get the factory ECM to work. But, I'd be willing to bet there are better systems out there that'll get you on the road sooner with less stress.


In a round about way, I kinda do this on my car. It's easier. That's the main reason. I'd rather leave the MAF sensor alone in a near stock intake configuration and back into injector data than trust what I think the injectors are doing and back into an airflow model....especially on cars that have nice big cams. Mine is sitting pretty at 18* of overlap. There's no way in hell I'm going to tune that thing to run 14.7 on my wideband at idle with 18* of overlap. That's just shooting raw fuel into the exhaust. So, I trust the MAF and set the IFR line in accordance with the rest of the tune at cruise and WOT. Although the WB reads 16+:1 at idle, I know it's pretty darn close because of the smell and the performance....and the fact that I trust the factory, screened MAF on a factory curve.

Straight up - it works for me and I feel like the car is better for it. That's why I do it.

Sarg

iTrader: (6)

I hear ya, but for now it is what I have. I am doing a custom 3 bar os in hpt. But I remember there being a load limit of some sort.

joecar

COS5 in EFILive has a TP VE (alpha-N) table that enables below some selectable RPM, this is for large-overlap cams.

rsz288

Hey Joe, great question, maybe human nature is the simple answer, ie:

Why do Voodoo (not picking on you Voodoo practitioners, simply an example ) and other pursuits of the make believe still survive and proliferate?

Because often people want to believe in wierd stuff vs the right stuff. Astonishingly so. Like those of that might understand searching for lost quantum bolts. .

Greg's work on injector characterization might represent authoritative and paramount knowledge on the subject, but plenty of people will argue with it and go their own way simply because they dont want to believe in it.

A recent example that a buddy encountered was an industry recognized producer of high end tuning products did not understand a question on injector characterization beyond simply IFR. They didnt "believe" the other parameters were necessary. Doh! :doh: