Holley COMMANDER 950 - Manual (Page 31)

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Figure 13 Fuel Map Showing Proper IAC Position
For more information on how an IAC works, see Appendix 1—Idle Air Control.
7. FUEL MAP TUNING (LOW SPEED)
The next step is to adjust the base fuel map. The method used requires that an oxygen sensor is installed and operating
properly. See Appendix 1—O
2
for VERY important information about oxygen sensor operation and installation.
Most of the base maps should be set so that the engine will go closed loop at idle with engine temperatures above 130° F.
See Section 1.20 to help verify these parameters.
If you do not thoroughly understand how an oxygen sensor functions and what closed loop operation is, it is highly
advised that you review Section 1.12 & 1.20 first.
The flow chart (Figure 16) describes the following method in a graphical manner.
To tune the engine at idle and cruise, we will have the feedback from the O
2
sensor tell us how to change the map. This
makes it very simple. Get the engine idling and up to operating temperature (at least 150° F). The CLT Mod Box should
be at 100 at this point. This indicates that you are not adding any extra fuel due to coolant temperature enrichment.
Bring up the main fuel map. Towards the top center of the map there is a box called “O
2
Mod”. This number will be 100
when the engine is open loop. When it is closed loop it will not be 100. This number tells you if the ECU is adding or
subtracting fuel from the engine to maintain a 14.7:1 A/F ratio. If the number is 90, for example, it means that the ECU is
subtracting 10% fuel from the base map. If it is 110, it means that the ECU is adding 10% fuel from the base map. The
following picture shows a properly tuned engine at idle with an O
2
mod of 89.9% (Figure 14).