SAFC - something doesn't make sense to me.

[Sharkcus]

I have read through all of the SAFC articles many times, but a question still lingers. Here is an example: 550's SAFC 16G 2g

Car idles fine with 450's. I put in 550's and it idles poorly. Right. Expected that.

So I go through a few tuning guides and attempt to bring my STFT to 0 (it's a 2g, so that would be 100% on a 1g) at 1000rpm. Right. Makes sense that I would need to lean it out with bigger injectors. In order to do that, I have to bring the 1000rpm point down to about -4%

It idles like absolute crap.

Following another guide in the tech section, i see that someone states to bring the fuel at 1000rpm up until it isn't studdering and idles fine. I do that (about 5% range) (the STFT is way off now)

So the car idles fine now.

So my question is this. Either I have a very fundamental misunderstanding of how the SAFC works, or I am going crazy. With bigger injectors, why do I need to RICHEN it up to get it to idle halfway decent? No boost leaks, no nothing...

Could the STFT readings be off? Even if they were, that still doesn't tell me why I am richening it up over stock WITH bigger injectors. Looking at others 1000rpm point settings, it appears I am not the only one with positive settings and bigger injectors.


edit: I should also add, I purchased the 550's used, maybe they need to be cleaned? I do see other people doing the same thing with the 1000rpm point though, which makes me wonder.

 

[CanadianTSi]

If your STFT is at 0 then your car should Idlfe Fine.

If not you have a problem somewhere else.

 

[weith1111]

I have basically the same situation. I was thinking it was more related to dead time. I'm fixing a couple other things that I know aren't working right before trying to diagnose. For reference I'm at +10 at 1k rpm on 550cc injectors, and still at 125% on the LFT, to go it to 100% I have to do +15! The car will run and idles lovely at -10 on the AFC, but when trying to pull away it wants to die. The LFT is maxed and I can tell it's choking with too little fuel. So back to +10 it goes.

 

[Sharkcus]

Ok, so I am not the only one. At 2k, -4 or so seems just fine... It's just at idle, it NEEDS to have over +3%

Next month I am going to replace my fuel filter and see if I can have my injectors cleaned and balanced. Hopefully that will take some of the myster out of this.

 

[weith1111]

I'm obsessive about getting things working right, but in the scope of it all, as long as you are running with good FT's at 3k-4k and have good AFR at WOT, everything will be fine. I mean my car idles for like 4 minutes a day...

 

[spyderturbo007]

Sounds like your O2 is taking a dump. If that is the case the O2 voltage will begin to drop to zero. The ECU will see a lean condition and begin to increase the FT's. In order to bring the FT's back down you will need to add airflow on the SAFC (i.e. move in the positive direction.)

But that still doesn't explain why it only started when you installed the 550's. Have you tried this:

1. Verify operation of the O2 sensor
2. Reset the ECU by removing the battery terminal
3. Set the lo throttle SAFC-II settings to -12% at 1k, 2k and 3k
4. Start the car and see what happens to the FT's.

 

[Sharkcus]

Good ideas. I have a brand new O2, but I never see it get much into the .90's at all, even at WOT. That would directly effect the trim too. I am going to reset the ECU first and see what happens. I'll keep you all updated with my progress.

 

[pneumo]

It's possible you guys might have a boost leak somewhere. A leak will allow extra air into the engine, the SAFC lets you compensate for it.

 

[Sharkcus]

I checked for leaks and didn't find any a few weeks ago, plus it holds boost just fine, but you do have a point, it would explain the problem. I'll do another test tonight.

 

[spyderturbo007]

That would directly effect the trim too.

I'm not quite sure what you are referring to here? If you are referring to the FT's at WOT, I wanted to let you know that the ECU doesn't use FT's at WOT.

 

[OB1]

On a 2G you need to be looking at the LTFT. The STFT is always bouncing around and to only track the STFT will have you constantly adjusting your Low throttle fule settings.

Adjust your Low throttle fuel setting by watching LTFT Lo(idle) and LTFT mid (cruise).


As you adjust your fuel setting, your STFT will immediately move in the same direction (leaner or richer) until your LTFT start to change, bringing your STFT back down to near zero.

You want your LTFT to be as close to zero as possible, not your STFT.

 

[Sharkcus]

I wasn't referring to tuning at WOT, I only stated that at WOT, my o2 readings barely go over .90 so I was questioning the performance of my new O2. I meant that a bad o2 (not ever reading rich) would directly effect the fuel trims (STFT)


Right now I am only concerned about the idling issue. I don't want to start tuning the high settings before I get the low figured out. That being said, I was under the impression that you only want to look at STFT when tuning idle and the low settings (1k, 2k... in the low throttle). If I bring my STFT to zero, I am at -12% @ 1000k. If I follow the guide and match up my STFT and LTFT ( http://www.dsmtuners.com/forums/showthread.php?t=58403 ) I end up with an even lower percent (-15% @1000k) which seems normal compared with other people's settings. BUT.... the car will not idle decent at anything below +3% and throws misfires at -15%. I think the previous comments are on to something, such as a boost leak (unlikely, but I will check again), a bad o2 (also unlikely...) and an ECU reset being needed. I am also going to send my fuel injectors off this week to have them cleaned, as I am not sure if they are even flowing decent.

One last thing to add. If I tune my 2k and 3k settings as they should be, they end up right in the -12% area, which is right where they should be. I'll dig into this more when I get home from work.

I will try to watch the LTFT instead and see what happens. Still doesn't explain why I am adding MORE fuel with BIGGER inejectors at idle... Very odd indeed.

Again, thank you all for these excellent responses.