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For an additional example, a higher performance engine with a torque peak at 5000 RPM would have a curve that would peak
very close to 5000 RPM. See the figure below for an example of a fuel map for a moderately built 502 cubic inch Chevrolet
engine. By having a fairly good idea of what the torque curve of the particular engine the system is being installed on, the user
can better custom tailor the Injection Volume curve in the increasing engine speed direction to match the fuel requirements of
their engine.
These fuel injection systems use an oxygen sensor feedback system. With these systems, most users can obtain excellent fuel
economy along with good driveability and performance. The purpose and nature of the oxygen sensor is to maintain the fuel
system delivery in a range very close to a stoichiometric mixture. In addition, the MPI PRO-JECTION system allows some
degree of adjustment from stoichiometric fuel/air mixtures. This system works very well on stock or near stock engines.
However, Holley engineers have found that some engines, typically very high specific output engines, may require a richer than
stoichiometric fuel/air mixture to run properly. These engines may need more fuel due to the fact that fuel is lost from the intake
track to the exhaust track during valve overlap periods when using a high lift cam with high overlap profiles. Since this type of
engine may require a richer stoichiometric fuel mixture than what the oxygen sensor will control to, these engines may run best
in open loop mode. The user may find that best performance of their vehicle will be obtained by using the oxygen sensor to tune
the engine slightly richer than stoichiometric and then making settings in the software or disconnecting the oxygen sensor to
allow the engine to run in open loop. This should only be necessary in the case where an engine has been custom built by a
high performance engine builder.
14.0 GETTING STARTED TUNING AND PROGRAMMING
14.1 Software Installation and Software Operational Description
An IBM compatible personal computer (preferably a laptop for portability) with EGA (or better) monitor is required for adjustment
with the Di system. The PC must have DOS level 6.0 or Windows 3.1 or Windows 95 to run the Holley software package. The
software is not designed to use a mouse with the DOS and Windows 3.1 Versions, but will run with Windows 95. The Holley
software package allows modification of the Spark Advance, Oxygen Trigger Voltage, Idle RPM Parameters, Temperature
Compensation tables, and the complete fuel map.
NOTE:
Read through the entire tuning and adjustment portion of the manual before attempting to modify any maps.
DANGER!
HAVE AN ASSISTANT TO MONITOR THE SOFTWARE PACKAGE OR TO OPERATE THE VEHICLE DURING
TUNING AND ADJUSTMENT. FAILURE TO KEEP A SAFE DISTANCE FROM OTHER VEHICLES AND
FOLLOW ALL SAFETY PRECAUTIONS. LAWS, RULES AND REGULATIONS CAN LEAD TO PROPERTY
DAMAGE, SERIOUS INJURY AND/OR DEATH!
14.1.1 Windows 95
1 - Insert disk 1 of 4 labeled for Windows 95.
2 - Select the START menu at the bottom left hand area of the computer screen.
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Troubleshooting
