Holley pro-jection 2D Installation And Troubleshooting Manual - page 7
6.0 SYSTEM OVERVIEW
The projection system actually consists of three systems; the air and fuel delivery, the fuel return system, and the electronic
control system. Because the ECU utilizes digital electronics, it is not affected by variations in temperature or humidity.
Although the digital ECU is pre-programmed at the factory, the amount of fuel delivered to the engine under various operating
conditions is user-adjustable through the use of five adjustments knobs located on the front panel of the digital ECU. These
adjustment knobs are used to tune the system. The Digital ECU has adjustments for Choke, Acceleration, Idle, Main, and High
RPM settings. By simply dialing in the appropriate fuel curve, fuel delivery can be accurately matched to the engine’s
requirements across its entire power band.
The fuel is pumped from the tank to the Pro-Jection throttle body through the fuel filter. At the rear of the throttle body is the fuel
pressure regulator, which maintains the fuel pressure at 15 psi (or any pressure you choose between 12 and 22 psi). Excess
fuel not injected into the engine is returned to the fuel tank via the fuel return line.
The ECU is factory programmed and controls the amount of fuel delivered to the engine by pulsing each of the two fuel injectors
for precisely controlled periods of time. The rate and length of time at which the injectors are pulsed is calculated from various
inputs such as engine speed, throttle position, engine coolant temperature, and an optional oxygen sensor. Below is a
Projection system layout of all three systems.
WARNING! The Digital Pro-Jection system is NOT recommended for high-speed, high-performance engine
applications.
Figure 1
NOTE: Although every possible precaution was taken in the design of the digital ECU to prevent interference from radio
sources, the use of solid core spark plug wires may interfere with the operation of the ECU. Holley recommends the
use of either suppression or spiral wound spark plug wires, such as Holley Part #’s 50-9800, 50-9801, or 50-9804.
7.0 REMOVAL OF EXISTING FUEL SYSTEM
1. Disconnect the battery and remove the flame arrestor.
2. Before disconnecting any vacuum hoses, it is a good idea to sketch out the vacuum hose routing. Using masking tape and
a permanent marker, mark all the vacuum hoses, vacuum sources and ports before removing the old fuel delivery system.
3. Remove and discard the fuel line that connects the fuel delivery system to the fuel pump. This will not be needed in the
installation.