SAFC tuning questions

[steve]

I received this question via PM and it really belongs here. Questions should be posted and links sent to wisemen or moderators if you are looking for answers so that everyone can see them and help.

I read all the tuning tips in the vfaq's but I am still a little confused.

When tuning with an afc setting the low throttle points only effects the low trim (1g) correct? I guess my question is, what changes the mid and high? Will changing the correction in the low throttle/high rpms effect them? Like low- 4,5,6,7k or is the mid and high trim corrections made from the high throttle corrections?

Another thing that confuses the hell out of me is when I make my corrections on the low they are positive+ but the high are negative- . I read that I should mirror the low settings in the high, but negative..
example: low/1.+5 2.+5 high/1.-5 2.-5 and so on.

Why am I removing fuel from the high when I had to add fuel to the low??? I dont know if I worded this right, I hope you get what I mean.

Well thanks in advance if you can find time to respond.
-Dave

No, the basic premise is wrong. The SAFC low throttle NE corrections effect closed loop mode. The entire range of fuel trims are covered.

Since you are really unlikely to be on the low throttle corrections at high RPM you just continue the lower RPM correction used while in closed loop for them. The high throttle corrections are for tuning the car rather than correcting for changed to MAFs and injectors.

You don't change the sign of the corrections when copying the setting from the low throttle to high throttle NE points. They should start out exactly the same. You start with the low throttle corrections copied over and then tune to the AFR you trying to get if you have a wideband or for knock, or both.

The only reason you would have corrections that change sign between low and high setting is because you leaks in your intake that cause you to suck in unmetered air under vacuum or leak metered air under boost. Fixing the leaks is something that should be done before tuning not with the SFAC.

 

[BIRDCLAWTSi]

so when i copy the low settings over, do i copy the settings exactly as they are for the lows?
all of my low settings are positive so therefor my highs should be copied over positive as well? that is what i really dont get.
I read a thread last night that showed the same corrections in the highs but they were (-) instead of (+).

 

[steve]

Yes you copy them exactly the same.

What your doing with the low setting is making the corrections needed to adjust for the changes from stock needed in order to get the car back to the point where the ECUs calculations from the airflow seen = the feedback from the O2 sensor. It's trying while it's in closed loop to hit 14.7:1 (or actually average it) which is the point where the O2 sensor switches. You adjusting the AFC to get the fuel trim to 100 (or 0 on a 2G) at each RPM balances out the basic fuel calculations (while messing up the ECUs idea of engine load but that can't be helped with an AFC).

Those corrections apply all the time so you copy them over to the high settings and if you leave the SAFC like that you will have a car that runs pretty much like stock (the timing is different because of the change to the ECUs idea of engine load) with the new parts. Most people also want to leak the car out from factory map and that's is what I call tuning.

 

[BIRDCLAWTSi]

thanks, i get it. i think what the problem i am /was having is that the injectors cant be 550's and the corrections i am making are way out of wack with other ball park figures for 550's and a 2g maf. so i didnt want to go so far from what i thought was an ideal area, correction wise for the injectors. it is a little frustrating that i got beat for injectors. now that i know what i am dealing with it should be a little easier to get this thing moving. the other thing is that i am tuning with my wideband and when i get the a/f ratio's looking good , the trims are a bit off. like 10% in either direction. i am shooting for 11:1 under full boost correct? at that point watching timing and knock. i just dont want to start that thread... I MELTED MY MOTOR. thanks again.