SD Tuning Map at Zero vs Map Airmass

[Haydos_87]

So gurus please explain when it is it that i would start to change the "Map at Zero" table. Let's just say i have my injectors scaled right and i have been using an lc-2 and logging.
Ive been changing the MAP per Airmass High Res table and been having good results but as i look at the same rpm vs cam angle i see the afr change quite a bit. Is this when i start using the map at zero and how does it work??

[IH8TOADS]

If you did a dyno run with a locked cam angle and your AFR was as commanded at say 70 inHG but not at say 60 inHG then your map per airmass is off. If you have very accurate measuring gear you can solve for it mathematically using two airflow points. It's been covered in the SD thread.

[rolls]

If your AFR/LTFT is on point at the majority of MAP values (at a specific RPM and Cam angle) but then goes off at very low MAP values.

Eg

at 2500 rpm -10degree cam

8.61 inHg = 0.9 lambda (this should be the lowest map value you have measured in this cell but not an outlier, eg you should have at least a few measurements at this value)

10 inHg = 0.95 lambda

15 inHg and above = 0.99 -> 1.00 lambda

Then your MAP at zero is off. You can calculate the change required via this calc.

fuel mass in lbs = ((map- "map at zero airmass high res") / "map per airmass high res) / stoich_afr)
0.0000183059 lbs = ((8.61 - 3.3) / 19800 / 14.64)

now you want the ECU to inject 10% less fuel mass in grams eg 0.00001647531 lbs

Do some algebra

"map at zero airmass" = (stoich_afr * "fuel mass" * slope)

"map at zero airmass" = (14.64 * 0.00001647531)

"map at zero airmass" = 3.35668

voila, you change your "map zero airmass" value at 2500 rpm, -10deg cam from 3.3 to 3.357 and your AFR should be much closer to 1.00

Now you need to make sure your datalogging has LOTs of values at that cell before trusting this data, your wideband must also be calibrated correctly which unless you have a few to compare it to you don't really know this.

Also this only works if your slope is perfect, eg at high MAP values your AFR is exactly on point. You can do the same calculation for "map per airmass high res" if your lambda is off by exactly the same percentage at all map values.

Personally I would do everything in the following order:

Injector data dialled in, eg offset, low slope, breakpoint, high slope are set in that order.

Then get your MAP slope set correctly, only then should you go modifying your map at zero.

Something else to remember if you have DFCO (fuel cut) conditions met then your AFR will be off on these cells, you need to ensure DFCO is disabled if you want to optimise your MAP at zero cells.

Good luck!

edit: Like IH8TOADS said if you lock your cam angle (set all values to a certain cam angle) then you can get better data as the cam isn't constantly moving interpolating between cells.

[misk]

that's some mint info rolls, helps having it laid out like that!

[IH8TOADS]

Ford's speed density system uses inHG and lb's, you'll need to stick to these units or convert.

[rolls]

Yes my bad, I had converted them in my spreadsheet.

[rolls]

Something else that is very important, you either use LTFT that has been dialed in, eg run for at least 80km of street driving OR use a wideband and LTFT disabled. You can't use a wideband if you are in closed loop as the ECU will be essentially adjusting the map at zero for you skewing your results.

What I recommend is disable LTFT and set O2 min temp to 4096?F if you are going to use a wideband. Then use wideband_afr / commanded afr to get your fuel trim error.

I wrote some software that helps visualise when you should adjust the map at zero. It will auto filter the data and show you the trend of map vs fuel trim/afr so you can determine if it is a constant error (map slope) or an offset error (map zero)

http://www.hptuners.com/forum/showth...d-density-maps

Here is a link to my spreadsheet that will recalc the offset based on lambda error.

https://dl.dropboxusercontent.com/u/...%20recalc.xlsx

[stevenbruzzBa]

Something else that is very important, you either use LTFT that has been dialed in, eg run for at least 80km of street driving OR use a wideband and LTFT disabled. You can't use a wideband if you are in closed loop as the ECU will be essentially adjusting the map at zero for you skewing your results.

What I recommend is disable LTFT and set O2 min temp to 4096?F if you are going to use a wideband. Then use wideband_afr / commanded afr to get your fuel trim error.

I wrote some software that helps visualise when you should adjust the map at zero. It will auto filter the data and show you the trend of map vs fuel trim/afr so you can determine if it is a constant error (map slope) or an offset error (map zero)

http://www.hptuners.com/forum/showth...d-density-maps

Here is a link to my spreadsheet that will recalc the offset based on lambda error.

https://dl.dropboxusercontent.com/u/...%20recalc.xlsx

Anyone got the spreadsheet there willing to share links dead