14.3 High RPM
The HIGH RPM adjustment knob allows the user to adjust the fuel delivery for engine speeds over 3000 rpm 50% above or
below the values that are set at the factory. This is accomplished by moving the fuel map either up or down along a diagonal
hinged line as indicated in Figure 13. Turning the adjustment knob clockwise increases the fuel delivery, while a counter-
clockwise rotation decreases the amount of fuel delivered to the engine at high engine speeds.
14.4 ACCEL Pump
The ACCEL PUMP adjustment knob allows the user to adjust the addition of fuel for acceleration 50% above or below the value
set at the factory. Rotating the adjustment knob clockwise results in additional fuel being added to the fuel enrichment set at the
factory, while rotating the adjustment knob counter-clockwise will result in less fuel being added during acceleration. The proper
adjustment is made while performing acceleration tests, which are described later on in this section.
14.5 Choke
The CHOKE adjustment knob allows the user to adjust the amount of fuel enrichment while the engine is warming up 20% above
or below the value set at the factory. Rotating the adjustment knob clockwise will increase the amount of fuel added while the
engine is warming up. Rotating the adjustment knob counter-clockwise will decrease the amount of fuel added while the engine
is warming up.
15.0 BEFORE STARTING THE ENGINE
WARNING! The adjustment knobs on the front of the ECU are precision manufactured parts and do not require a great
deal of force to turn. Do not apply excessive force to the adjustment knobs. Full adjustment range for the
knobs is 3/4 of a turn.
Figure 14
1. After all electrical connections have been made, double-check all connections to ensure that they are tight and secure.
2. Reconnect the battery.
3. If installed, remove the oxygen sensor harness from the digital ECU by unplugging the harness from the rear of the ECU.
4. Although the adjustment potentiometers on the front of the digital ECU were set at the factory in the null position, check to
ensure that they were not moved. If necessary, rotate the potentiometers, so that they are positioned as in Figure 14.
5. Turn the ignition key to the “RUN” position. DO NOT START THE ENGINE. Listen for the fuel pump. The fuel pump
should run for several seconds before shutting off.
6. Turn the ignition key to the “OFF” position.
16.0 SETTING THE MECHANICAL IDLE
The setting of the mechanical idle speed is critical in the operation of the Digital ECU and is best accomplished by using a
tachometer. If your vehicle is not equipped with a tachometer, Holley highly recommends one be used. To adjust, follow the
instructions carefully.
