Air/Fuel Ratio Adjustment

[kylelavergne]

Can someone please explain what should be adjusted 1st...Air/Fuel Ratio or Spark. I'm wanting to advance my spark bc i strictly run 93 octane in my truck. Thanks!

[Wheelz]

The airflow calibration must be correct for the correct timing cell to be used with the ls1b controllers. Make sure the tune has the proper stoich programmed for your fuel, (typically 14.7 for pure gas and 14.1-.2 for 10% blends)

If it's a bone stock engine the airflow calibrations will be close unless your having hardware issues, as in failing MAF for example. If you don't see excessive LTFT's when logging, it should be good enough to play with the timing

[kylelavergne]

Thanks for the reply Wheelz. What table would i look for to adjust stoich for my fuel? & what would be excessive LTFT's? I already advanced by 3 deg without messing with the airflow or the fuel & i only get about 0.1-1.0% knock retard but only at high rpm range.

[joecar]

B3601 sets stoich AFR.

Outside the range +/-5% can be considered excessive LTFT depending on purpose.

[kylelavergne]

But how do i measure LTFY's Joecar?

[joecar]

Hi Kyle,

( sorry I haven't read any emails for a couple of days, I intend to catch up tomorrow )

Log the pids LONGFT1 and LONGFT2.

The PCM does this (in this basic order):
- calculates cylinder airmass using MAF and/or VE,
- looks up what AFR to command from CL or OL and/or PE,
- from those calculates fuelmass required,
- applies LTFT to fuelmass,
- calculates injector pulsewidth to spray fuelmass.


So regardless of what the commanded AFR/fueling tables contain, any non-zero LTFT indicates an error in MAF and/or VE tables...

to tune the MAF and VE tables, you have to isolate the airmass contribution to one of these (MAF or VE), and then apply the logged LTFT or wideband correction.

Note that LTFT corrects ahead of wideband, this means if you want to correct using wideband you have to disabled CL/LTFT/STFT/SOL.


More info: see posts #4 and #29 here: Summary-Notes (http://forum.efilive.com/showthread.php?14188-Summary-Notes)

[joecar]

So first you get the MAF and VE tables correct, and then you look at spark timing (it will probably be ok unless you have a radical build).