680's Leaning out????

[BoBBOSVR4]

I fired up my car for the the first time after a costly rebuild. I am running 680 injectors, and was told that i would have to lean them out a lot on the afc to get the motor to fire. I set the low throttle pts to -20%, had the innovative wideband hooked up, and turned the key. The motor fired right up, the afr was 16 or so. I changed some things and when i fired it back up, it seemed that the closer i got to 0 the closer the afr got to around 13-14. At this point i just want to get it tuned well at idle. Any suggestions? I figured with injectors that big i would have to lean out the afc more than just a couple of % pts.

I am also running a 2g mas, sorry forgot to throw that in there

 

[Blk_99gst]

The easiest thing to do would be to put your stock injectors in, and get the motor running properly with those, and not have to complicate matters of tuning 680 injectors with firing up a motor for the first time.

The problem is you really can't use a wideband o2 unit to help you with low throttle/idle tuning. The ecu will be in closed loop mode, meaning it adds fuels, check to see how it did using the o2 sensor, and then adjusts fuel delivery using the fuel trims. So you started out at -20%, which is probably where you need to be. And as you went closer to zero, the ecu used it's fuel trims (removing fuel via the fuel trims) to try and keep everything in check and reading a stoichiometric 14.7:1 out the tailpipe on the wideband. Anyway, what you really need is a obdI pocketlogger unit, so you can see the actual fuel trim settings, and adjust the low safc setting to get the fuel trims to as close to 100% as possible.

 

[BoBBOSVR4]

thanks a lot. I think that makes more sense now

 

[kpt4321]

It's because you have a 2g MAS installed, that will show about 20% less airflow, which will bring the SAFC much closer to 0%.

 

[Blk_99gst]

It's because you have a 2g MAS installed, that will show about 20% less airflow, which will bring the SAFC much closer to 0%.

I thought in 1g cars (vr4's) that a 2g maf and 550's are the combo that kind of cancel each other out. He's running 680's; there has to be some negative safc action with the 680's...

 

[herostar]

well my pte 680's are set around -20 at low throttle... so around zero sounds about right

 

[BoBBOSVR4]

so using my innovative at idle to tune won't work as well as a logger. I mean at idle i can look at real time air fuel ratios and try and tune from there. Right?

 

[LandoAWD]

It's because you have a 2g MAS installed, that will show about 20% less airflow, which will bring the SAFC much closer to 0%.

[nitpick]

Is this a worthwhile addition to the S-AFC .xls file you created?

[/nitpick]

 

[kpt4321]

I didn't create that, I just helped its auther verify that the technical information was correct.

 

[Blk_99gst]

so using my innovative at idle to tune won't work as well as a logger. I mean at idle i can look at real time air fuel ratios and try and tune from there. Right?

Yes, the innovative doesn't really work for anything other than WOT runs. Here's why. Under normal idle and cruising speeds, the ecu is in closed loop mode, meaning that it delivers fuel, checks the combustion via the front o2 sensor to see how close to 14.7:1 it got. If it's off, the ecu will adjust its fuel trims to either add more or less fuel for the initial calculation. So let's say you are -20% on the safc. The ecu see's 20% less air coming, it adds fuel, looks at the o2 sensor, and sees that things are way too lean. It will then bump up it's fuel trims to say +10% (10% richer) to compensate. In the above senario, the end a/f ratio out the tail pipe will still be 14.7:1, but your low settings aren't in tune because the ecu is having to adjust fuel trims a lot. I would say a safe place to be would be + or - 5% from 0% for a 2g car; for a 1g car, fuel trims should be at 100%, plus or minus a little.

So in the above situation, if you had a logger. You could look at fuel trims, see that +10% was out of wack, and could adjust the safc from -20% to -10%, then over time the fuel trims should go from +10% to 0%. And during this whole time, the LM-1 will still read 14.7:1 out the back of the tailpipe.