Miata Mailing List: September 1998, Message #90

sponsored by

Greg,
  Tuning hints for you:

1. Set the target air/fuel ratios in the A/F table located under EGO 
parameters. Initially set EGO authority to +/- 0.4 to allow for really out of 
tune areas. As the volumetric efficiency table is tuned, the EGO authority 
can be "tightened" to a value closer to zero (i.e. +/- 0.05 or 0.1).
2. Using the monitor screen and an assistant, have the assistant call out the 
MAP numbers while you attempt to hold a constant MAP and RPM.(i.e. 4000 rpm 
and 100kPa; 6500 rpm and 164 kPa). As a side benefit, note how this procedure 
also enables you to test your brakes for fade resistance when hot. ;-)
3. Have assistant note the EGO CR (EGO correction factor)value after it 
settles (i.e. +0.11 or -0.15 or 0.02) and write down that value. As the EGO 
value approaches zero, it indicates you have tuned the volumetric efficiency 
table. Repeat this for the breakpoints you are trying to tune. Tune the lower 
rpm and MAP breakpoints first, then step across and up the table (tune bottom 
left to upper right). The TEC will linearly interpolate between breakpoints 
so you want to gradually expand the operating envelope in a safe and 
consistent manner.

4. In the Volumetric Efficiency table, enter the EGO CR value noted by your 
assistant. In offset mode, you should have a setting equal to the EGO CR 
value. In absolute mode, the setting should be equal to 1+(EGO CR). 
  Example 1: EGO CR = -0.18. Set the VE table entry corresponding to that 
breakpoint to -0.18 (offset mode) or 0.82 (absolute mode).
  Example 2: EGO CR = +0.14. Set the VE table entry corresponding to that 
breakpoint to +0.14 (offset mode) or 1.14 (absolute mode).
  Example 3: EGO CR = 0.01. I'd leave the VE table entry alone (should be a 
default = 0 (offset) or 1(absolute)). In this case the target and actual 
air/fuel ratios are very close.
5. Re-test your car at the breakpoints. If tuned correctly you should have on 
the monitor screen:
  Example 1: GAMA 0.82, EGO CR approaching zero.
  Example 2: GAMA 1.14, EGO CR approaching zero.
  Example 3: GAMA 1, EGO CR approximately 0.02.

  Target air/fuel table entries are the over-riding priority. Volumetric 
Efficiency Table modifies the fuel curve to reduce the EGO CR correction 
factor to a small "envelope" around your target air/fuel ratio.

  In monitor screen, ensure the "Bar" setting is equal to your sensor value. 
I.e. 1 for NA, 2 for max 14.7 psi boost, 3 for 29.4 psi boost. If, like me, 
the setting is at 1 but a 2 bar sensor is installed, at zero inches of vacuum 
(no boost) the monitor screen will only show 52 kPa instead of the actual 104 
kPa. (Duh!). Setting the bar value to "2" allowed me to get the correct 
pressure readout.
  Hope this helps.

Regards,
Barry