Need help with understanding MAF adjustments.

[Redline Motorsports]

Its seems that many tuners adjust the tail end of the MAF {B5001} table and I am trying to undertand when that table should be tweaked. Is it true that the MAF typically doesn't get touched from stock calibration if the intake system on the inlet side is not touched??

This also leads into the question of WOT fueling; can both the {B5001} and {B3618} be used togther?

Howard

[redhardsupra]

when? anytime you adjust your VE table. these who don't adjust it from stock, are...umm...suboptimal.
yes, you're using PE to get the ratio between air and fuel. of course if your maf gives you a wrong number for the airflow, then your fueling will be off too. (that's why calibration of MAF is crucial, especially since wot is 100% MAF derived).

[dfe1]

Everyone who tunes an engine develops a specific approach that seems to work best for that particular individual. Consequently, there are about as many "right" ways to tune as their are wrong. One of the "problems" I see with FlashScan is that it offers so much capability and is so easy to use, people start making changes just because they can. I think changing MAF calibration generally falls in this category. I have to assume that the engineers at Generous Motors spent quite a bit of time on the original calibration. That being the case, one has to assume that MAF readings are an accurate measurement of the amount of air flowing through the sensor. Unless the MAF is changed or modified, what's the point of altering the calibration-- unless you're trying to fudge the data flowing to the PCM? (Note the FlashScan instructions note that MAF calibration should only be altered if the MAF has been modified.)

On the other hand, it is frequently necessary to do a bit of fudging in order to get LTFTs in range. However, in my experience, you can get the AFRs you want by working only with VE or with VE and IFR. In the end, it really doesn't matter how you achieve the desired results, as long as you achieve them. I just think that using MAF calibration as a tuning device, as opposed to as a correction, is not the best way to go.

If you're running out of MAF range, the easiest approach is treat the system as speed/density once the MAF range has been exceeded and use the PE table (B3618) to add the amount of fuel necessary to obtain the desired AFR.

[joecar]

If you got IFR table and VE table both correct, then while still in Auto VE Tune mode, compare MAF airflow with GM.DYNAIR (PCM calculated airflow based on VE and not MAF); if they're different, then the MAF table is out.

[redhardsupra]

joecar: dead on!
dfe1: your IFR/MAF tweaks make baby jesus cry
no fudging is required if you know all the parameters. there are many ways to skin a cat, but some of the methods end up with a much bigger, cleaner skin

[Dirk Diggler]

or you can build a new maf table based on BENS using an external and hopefully accurate WB that measure the ratio betweer AIR and FUEL. I wouldnt give GM to much credit as these car are set to run way rich from the factory WOT 11.75:1 with castrated values for timing (01-02) if you ever verified that on a stock car you will soon see how far they are out.

[dfe1]

dfe1: your IFR/MAF tweaks make baby jesus cry
no fudging is required if you know all the parameters. there are many ways to skin a cat, but some of the methods end up with a much bigger, cleaner skin

I disagree. In my experience, there always seems to be some fudging required unless you want to spend a lifetime tuning an engine. If yo think IFR/VE tweaks make baby Jesus cry, you should see what MAF tweaks do to him.

[Dirk Diggler]

LOL he said IFR/MAF tweaks make baby jesus cry and I think he is referring to those being used as the only two tables to tune car.

My tuning procedure goes as follows

1 Unplug maf
2 fit wb to the car
3 tune the ve tables using bens * 3-4
4 plug the maf back in and watch the WB read in excess of 10% lean
5. Use a map (freq vs Ben) and apply the ben back to the maf table * 3-4
6 verify actuall = commanded pt and wot
7 put car back in closed loop
8 watch the shit eating grin on customers face when you give them back a car that doesnt smell, buck, accelrates smooth and many more.....

[jfpilla]

Joe,Red,Dirk,
I'm with you. IFRs and VE's are the absolutes. Dirk, you mention looking at stock settings. There's a lot to be learned from them. For eaxample,IFRs for same size injectors are always the same. Unless IFRs are correct PE values will be further off.
dfe1,
Fudging may or may not be needed regardless of the methods but it is for sure necessary if you do a "work around" tune and then the issues that remain, that people put up with, are sure to arise under changing conditions. At my age a lifetime is not too long but I have put in the time to get it right. I think we do it ourselves because the PROs don't have the time to get other than an adequate tune. Unless your willing to pay big $.
The only tables I have used for cruise tuning are: VE,MAF,DES.AIRFLOW,TIMING,IFR and STARTUP FRICTION.
Joe
PS If you drag race have you noticed you may not always have cell 22 lock at 0? Heat soak can cause your trims positive if thet are set too close to 0. Mine are set at -6 at 0*C IAT. This generally is enough since I don't race in the hot summer.

[Dirk Diggler]

With all the access and different tables EFILive has given us some need to abandoned the LS1Edit way of thinking eg (IFR and MAF with PE values that wont or dont represent a real AFR or all idle issue deal with in the RAF table when we have a few more to choose from for different conditions ie startup)