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GOOD! DRIVE TO
ANOTHER AREA ON
THE FUEL MAP
“O2 Mod” ON THE
FUEL MAP IS…
LESS THAN 85 MORE THAN 105
SUBTRACT FUEL
PULSE WIDTH* AND
SMOOTH
SURROUNDING
CELLS**
BRING UP THE
SPARK MAP
DOES THE
ENGINE RUN WELL?
YES
BETWEEN 85
AND 105
NO
SUBTRACT
ADVANCE* AND
SMOOTH
SURROUNDING
CELLS
DOES THE
ENGINE RUN WELL?
YES
NO
ADD FUEL PULSE
WIDTH* AND
SMOOTH
SURROUNDING
CELLS
ADD ADVANCE*
AND SMOOTH
SURROUNDING
CELLS**
* The actual amount of fuel or
timing advance that needs to be
added or subtracted depends
upon how far the map is off. If
the engine runs worse, go the
other direction and see if it
clears up.
**Always listen for pinging (pre-
ignition). Stop driving
immediately, bring up the spark
map, and subtract ignition
advance in the area pinging is
encountered.
Note: This flowchart is slightly simplified. See
accompanying text for details.
Figure 16 EFI Tuning Guide—Idle and Low Speed Cruising—Closed Loop
8. FUEL MAP TUNING (HIGH LOAD AND RPM)
Once the idle and cruise portions of the map are tuned, higher loads and wide-open throttle (WOT) can be adjusted.
These areas need to be approached with caution as an excessively lean mixture can cause engine damage. Running
closed loop at wide-open throttle will cause the air/fuel ratio to be too lean and can damage the engine. For this
reason the engine must be run open loop.
The following procedure describes how to tune wide-open throttle. This method is fine for most naturally aspirated
performance vehicles. If you have a supercharged or turbocharged engine, the safest method of tuning would be to use a
wide-band oxygen sensor in conjunction with a chassis or engine dyno.
First, make sure the engine is set to go open loop at the correct throttle position. This is usually at about 2/3’s throttle.
Forced induction engines will be around 20% opening. With the ignition on and the engine off, open the throttle 2/3’s
open and note the TPS value. Then go to “Hdwr Settings” and “Oxygen Sensor”. Enter this value under “Max TPS for
closed loop operation”. This will change the engine to open loop above this number, allowing for the fuel to be richer than
14.7:1. Keep in mind that the fuel delivered will correspond to the value programmed in the fuel map. If it is too lean, you
will damage the engine.