onfire

iTrader: (17)

Why spend the time (other than the fun factor to correct it) to auto VE tune a car with ltrims of -6 to -12? Obviously, 0 to -4 is "desired".....but what's the REAL benefit. If WOT is properly tuned on a wideband....you're not going to pick up hp.....so why care if the ltft's are -10.....let the computer do the job.....

Just a Devil's Advocate position...

joecar

You might be wanting to toss the MAF and run SD.

onfire

iTrader: (17)

A change in OS is a valid reason, especially sd.


In non sd, why fool with it? Let the computer trim the fuel back to 14.63af with the trims at part throttle.....who cares if it take a -4 or a -13 ltrim to reach 14.63???

Let's hear some arguments.

brad8266

iTrader: (23)

The closer zero they can concistently stay, the less work the computer has to do. I do understand your arguement though, a lot of people have OCD when it comes to tuning trims. I just try to keep mine below zero. Also the more dialed in the trims are the closer your WOT AFR will be to what is commanded.
Example: If the PE table commands 13.0 at WOT and you actually read 14.0AFR with a wideband, then you should go in and dial in VE and MAF so you get what is commanded. I consider it to be the ghetto way to tune if you just leave the VE and MAF and just adjust the PE table till you get what you want. Thats what they usually do at a dyno tune and in my opinion thats not the right way to do it.

onfire

iTrader: (17)

This is ALL for discussion.....don't want to offend anyone.

Anyway, why would the wot commanded be more accurate with a -12 trim vs a -2 trim...as long as they are negative cell 22 will go to zero and not alter anything.

Also curious why you feel altering VE or MAF is less a bandaid than the PE table....do you feel it has a better resolution since PE is in 400rpm increments?

To me, altering a table is altering a table unless there is a benefit to alter a particular table. More resolution, etc would make sense.

Comments?

foff667

iTrader: (2)

This has been discussed in the past...bottom line is theres 100 ways to skin a cat. Personally when working on ls1's though I usually throw them into open loop SD tune the ve, then enable the maf and tune that throw it back into closed loop maf & the PE multiplyer will match the actual afr that i see with my wideband or within 1%. It doesnt take much longer and your basically correcting the ve & maf to match the car. Some claim to see an improvement in gas mileage(might be placibo effect) but I just do it as to not fool anything basically...in the end all the planets(tables) are aligned.

P Mack

iTrader: (6)

The reason is the ltft's make their corrections over broad ranges, for example fuel trim cell 11 covers 2400 rpm to redline and 60 to 79 MAP. That's a huge range of rpms to only have one correction. What if you're ve table is off +5% at 2500 rpm, but off -10% at 4000 rpm? Chances are your ltft will be -5% (because you spend more time driving at the lower end of the rpm range). So your fueling calculations will be a total of 15% off at 4000 rpm. You can't trust your ltft's to be the right correction for all rpms because they are so broad. It's like Homer Simpson trying to dial a phone number but his fingers are too fat to press the individual buttons.

brad8266

iTrader: (23)

Forget fuel trims for a second. Lets say you dont mess with VE or MAF and your PE table is commanding 13.0 AFR. Now you go out and log a few WOT runs and your wideband is telling you that the AFR is not at what is being commanded.
From here you have 2 options: 1-Adjust VE and MAF to make them accurate and to reflect the actual airflow entering the engine, when done right will put your actual AFR to what is being commanded.
2- Simply leave MAF and VE alone but just mess with the PE table to get it where you want. Doing this you might get your actual wanted AFR of 13.0 but you will get it while commanding say 12.0.

My OPINION is that the right way is it do number 1. I say this because then MAF and VE will be reporting accurate actual airmass entering the engine. Like stated though there are 100 ways to skin it.

horist

1 reason it's good to have a valid VE table is it's easier to use math then to compute your commanded AFR

If the VE table is 100% correct, then putting a PE value in for 12.8:1 should yield an actual AFR close to that... whereas if the VE table is 12% off, the actual AFR could be that far off too

Plus w/an accurate VE table you can accurately dial your MAF in so that again at WOT math is used more instead of guesswork

Doh, just saw the post before mine Repeat heh

brad8266

iTrader: (23)

onfire

iTrader: (17)

All great responses. Thanks.

Now, if you complete an auto VE tune and get the 0 to -4 ltrims, why would you ever touch the maf scale since it's just a sensor? If it's not modified, the frequency is bench calibrated to "report" 0 to 512 g/s. Seems like you would never touch that calibration.

brad8266

iTrader: (23)

Because the MAF is used a LOT rather than the VE table. They are used in conjunction with each other. To operate best efficient both of the tables need to be dialed in.

If you did an auto VE tune and your trims were good afterward and you then plugged in the MAF that has not been dialed in your trims will become off again. Once airflow mods are installed the calibration of the maf will be thrown off.Trust me on that, I have been tuning the MAf for a while now.

foff667

iTrader: (2)

maf is used for most fueling under 4000 rpms & all for over 4000 rpms so if its not spot on when using it that pe table wont be either

onfire

iTrader: (17)

Again, I appreciate the responses....helps to think through the variables.

You would think that a maf sensor that is calibrated on a bench to report freq vs flow would be like a wideband, etc. Just report what is flowing. Interesting that it needs to be tuned if it's not modified (like removing the screen) just to report freq. If you used a large cam and had some typ reversion down low....may be.....

Alll good discussion.

brad8266

iTrader: (23)

I used to think that about the MAF too. When you actually go and check out what happens when you adjust the calibration then you will become a firm believer in the fact that the MAF does need calibration when the car is modded.