IFR/VE table scaling - anyone done this? I'm stuck.

[Mr. P.]

Hi Gents -

I'm stuck, and I could really use some feedback on my tuning approach; vehicle is 2003 Silverado SS (LQ9) w/ Paxton Novi-1500 supercharger, 72# injectors, ARH longtubes, and 3000-RPM converter. Tune is COS 3, CLSD with 2-bar MAP sensor.

The first step I took was to calculate the new IFR for the injectors - the stock value was "3.179688", and using Marcin's IFR spreadsheet I plugged in a value of "9.335938" and began the AutoVE process. The result was that the 'shape' of the main VE table grew to Everest-sized proportions, and in-turn my transmission was kicking like a mule pretty-much all the time. After some research I decided to try VE Scaling, and I lowered the IFR value to "8.031250", which in turn (after another round of VE tuning) lowered the main VE table enough to where the transmission was no longer acting-up.

I realize now that there are many 'downstream' tables which also need to be "scaled", including the spark timing tables. I drive the truck daily, and for the most part it's pretty driveable however it won't take more than 2/3rds-throttle without mal-combustion of some sort, and in a lot of part-throttle situations the truck acts pretty "flat", it makes a lot of noise but is gutless so I am suspecting that at a minimum my main spark table is all screwed-up.

I am facing either:
(1) map-out all the other related tables and rescale them too, then proceed with tuning;
(2) keep the scaled IFR/VE tables I have, and rent a load-bearing dyno and completely map-out the timing table;
(3) abandon the scaled VE idea, and start over.

So my questions are: Should I continue on the path I have chosen and scale all these other tables too, if so has anyone else compiled a list of tables I need to rescale? Or is "VE Scaling" a flawed approach?

Thanks,
Mr. P. :)

[joecar]

Hi Mr.P,

Something must have gone wrong, post your tune and log files.

[Mr. P.]

... post your tune and log files.

OK, if you promise not to laugh :D

I don't really have a "sexy" log file - this is just a small stretch of low-speed driving through a freeway construction zone, some transient driving but no WOT...

I am also replacing the PLX WB02 with a NGK AFX unit this weekend, and changing Stoich in the tune from 14.6 to 14.1 because damnit there is no "real" gas in Texas anymore. :( That difference in WB02 BENS is probably explainable because I was (unknowingly) running E10 when I thought I was running E0.

Anyways - yeah would love your feedback if you have time to take a look.

Mr. P.

[redhardsupra]

Go back to basics: why do you get insane VE values? Usually when the fuel system isn't able to give it more fuel when asked to, the trims/AFR will tell you to keep upping the VE values, so you keep upping them, no change in actual fuel delivery is made, and you end up in a crazy loop. That's because you're using VE as a direct tool to change your IPW, and it isn't. A lot of standalones have a pseudo-VE table, that's really a IPW table with some funky scaling thrown in. That's not how it works here.

First figure out if you're in control of your fueling. If you give your VE 10% more, is your AFR going up 10%? How about -10%? Do they differ? If you're not in control of your fueling, all subsequent tuning is a waste of time, so make sure your fuel system works right. Check if your voltage stays up under heavier load. Check if the injectors flow what they say they do AT THE PRESSURE YOU'RE RUNNING. not at nominal, but actual. If all these check out cleanly, then and only then it makes sense to proceed. I'll look at your logs after work, but the principles are always the same, so check them out first.

[Mr. P.]

Thanks for the sanity-check Marcin, I appreciate the feedback and I will investigate that. Being completely truthful, I have not mounted a fuel pressure sending unit yet, I will be doing that this weekend to additionally log the behavior at the fuel rail.

- Steve.

[5.7ute]

Good advice Marcin.
IMO scaling is only necessary when a pcm hard limit prevents you from being able to control fuelling/ spark accurately. When logging I use a calc pid to calculate from dyncylair.dma to airflow in G/sec. If you hit the 511 G/sec limit then look at scaling.