Holley COMMANDER 950 - Manual (Page 8)

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Ball-on-a-stick injector. This metering design is mostly used in the director plate application. The seal is
achieved between a conical seat and a spherical plunger. The director plate has the function of metering the fuel
and generating the required spray geometry. Fuel flow is adjusted by the size of the hole machined into the
director plate and the spray geometry is adjusted by the orientation of the holes in the director plate. Because the
metering components are not exposed to the intake manifold environment, the injector is less susceptible to
carbon deposits. All Holley injectors are ball-on-a-stick style.
According to the solenoid design and metering requirements the injectors are further defined into two main categories:
1. High-impedance injectors 2. Low-impedance injectors
1.6.3 High-Impedance Injectors
Depending of the brand of the injector, the electric resistance of the coil is in the range 12 to 16 Ohms. In general the high-
impedance injector are rated for static fuel flows of 12 to 50 lb./hr. The high-impedance injectors are used with ECUs that are
designed with saturation injector drivers. The advantage of using saturation drivers is that the currents running through the
ECU circuits and the injectors are relatively low, thus generating less heat. The disadvantage of saturation drivers is that the
driver has a slower response time, which could affect the full utilization of such a system at very high engine RPM (two stroke
engine applications and four stroke engine applications of 10000RPM and above).
1.6.4 Low-Impedance Injectors
Depending of the brand of the injector, the electric resistance of the coil is in the range 1.2 to 4.0 Ohms. In general the high-
impedance injector are rated for static fuel flows of 55 to 160 lb./hr. The low impedance injectors are designed to be run with
an ECU that employs peak and hold injector drivers (also called current sensing or current limiting drivers). The advantage of
these drivers is that they limit the current in the injector and therefore reduce the heat generation in the ECU. In general, most
bottom-fed injectors are of the low impedance design.
1.7 Manifold Absolute Pressure Sensor (MAP)
The map sensor represents the intake manifold vacuum gage for the ECU.
The sensor is a three-wire sensor located on or attached to the intake
manifold. The function of this sensor is to measure the changes in the intake
manifold air pressure and generates an electric signal that is proportional to
the change of pressure. There are basically three types of Map sensors: 1bar,
2bar and 3 bar. The 1bar map sensor is for naturally aspirated engine
applications. The 2 and 3bar sensors are for forced induction engine
applications (turbocharged or supercharged). The 2 bar sensor is for
applications up to 15 psi forced induction pressure and the 3 bar sensor is for
applications up to 30 psi forced induction pressure. This signal is fed into the
ECU and is used to:
• Adjust the fuel delivery
MAP sensor
• Spark ignition calculations
NOTE: Map sensors read vacuum as kPa (Kilo-Pascals: metric units for pressure). Please see the Map Value to
Manifold Pressure Value chart on page 74 in Appendix 5.
1.8 Throttle Position Sensor (TPS)
The TPS is a three-wire sensor that is mounted on the throttle body assembly and is actuated
by the throttle shaft. The TPS is basically a variable resistor (potentiometer) that sends a
voltage signal to the ECU that is proportional to the throttle shaft rotation. When the throttle
shaft is open the sensor emits a high voltage signal and when the throttle shaft is closed it
emits a low voltage signal. The voltage signal from the TPS changes between approximately
0.45 V at idle to 5.OV at wide-open throttle.
Throttle Position Sensor