This folder contains all combinations of wiring options for injectors on Orion. These drawings are made for the high end harness and may differ in wire colours to other harnesses. consult your harness layout further in the manual. The main choices are, no of phases, low or high impedance, single or dual injectors per cylinder and the type of injection namely Batch, Split-sequential or Full sequential injection. Each folder contains its different variations for your engine. Note that the drawings are generic and you have to fill in your own firing order to see which wire colour goes to which injector. Print the document and write on it before you begin. Also note that combinations included in this manual may or may not be available for the hardware class or Brand type.

Fuel Injector explanations

The fuel injector outputs drive the fuel injectors to allow measured amounts of fuel into the engine. These signals are on/off control signals that are varied by duty cycle. The more fuel is required the higher the duty cycle will be. The injectors are connected to common positive and the drive signals from the ECU is ground signals.

Operation
The injectors are solenoid valves that are opened by current to let fuel pass through the nozzle. The nozzle has a spray pattern that will help in atomizing the fuel with air. This in turn will make a combustible mixture.

Injection types

Batch Injection
With this method, injector drivers are being pulsed at the same time once or twice per revolution. Very rare firmware from Spitronics, although not preferred, can use this method. However, fuel metering and timing is done very accurately and should still give excellent results. Split the injectors in groups to divide the current evenly between the available driver outputs. For bigger engines keep the mean supply current below the current capability of the drivers of that product. (See specifications.) Note: More outputs are available in the intermediate and advance units. (See specific wiring diagram.) The biggest disadvantage with this method is the fuel pressure pulses due to uneven tapping. Advantage is easy wiring.

Split Batch Injection
With this method, two injector drivers are being pulsed 180° out of faze. Although not preferred, fuel metering and timing is done very accurately and should give excellent results. Split the injectors in two groups to divide the current on the 2 driver outputs. Put alternate numbers on the firing order together to ensure a more even fuel distribution. For bigger engines keep the mean supply current below the current capability of the drivers of that product. Note: More outputs are available in the intermediate and advance units. (See specific wiring diagram.)

Split Sequential Injection
This method will inject on the two cylinders that move up and down together simultaneously and then in sequence on the other cylinders at the same position. Injecting once per revolution and will start at BDC or it may be adjusted otherwise. Fuel is injected very accurately and excellent CO adjustments can be achieved. The advantage of this method is that each cylinder receives its fuel under the same conditions, resulting in very smooth idling and revving. It is definitely better on power and consumption than the batch injection method. Injectors are wired in the same sequence as wasted spark. The fuel is distributed more evenly from the fuel pump and pulsing of fuel pressure comes to a minimum. The ECU only requires half the amount of drivers than cylinders on the engine. (See driver selection chart on how to combine these injectors.)

Full Sequential Injection
With this method each injector requires a driver. Fuel is injected once in 2 revolutions and normally starts at Bottom Deck Centre (BDC). Note: This feature is mainly for engines up to 8 cylinders. Disadvantage is that this method does require the Cam or home pulse to sink injection with fazes and low impedance injectors require a ballast resistor. Advantages are better fueling at lower RPM and longer duty cycle makes for more accurate measuring on large injectors. If you don’t have a home pulse it can still do full sequential injection but injection is not slinked on stroke. In these cases, start injection degrees can be set at BTDC just after the intake valve closes. (See wiring diagram on how to combine the injection methods.)

Throttle Body Injection
With this method, injectors are situated at the throttle body. The first generation injection systems used this method. It is important to inject in the right sequence especially on the 4 barrel systems. Some injectors are aimed at certain ports and must be pulsed in sequence to get a smooth distribution of the fuel mixture. (See specific wiring diagram to ensure the correct injectors are on the correct drivers.) Advantage of this method is easy to convert carburetor engines to fuel injection.

Injector Sizing
Sizing example: 5 cc fuel is required for every 1 HP. This means that an 8 cylinder 600 HP requires 600 HP x 5 cc / 8 injectors = 375 cc/min. This is assumed at Lambda 1.00 (14.7 AFR) so if you are running richer, the desired Lambda reading needs to be taken into account. This calculation is based on information from the internet and should be researched with other manufacturers. It is merely as an example.

Resistance & Current
Different injectors have different resistance from 0.5 ohms to 16 ohms. This means that they require different operating currents and wiring circuits to open them. The Spitronics ECU’s were designed for high impedance injectors. They draw 1 Amp each and can be connected together on the drivers in parallel. (See specifications on how much current the drivers can handle between the different products.) Low impedance, 3 to 5 ohm injectors, require current limited drivers to peak and hold drivers. With a minor wiring difference, the ECU’s can do low impedance injectors connected in series. They draw 4 Amp each but in series they draw 2 Amp. Again, see the specifications on the ratings of the ECU’s. If you want to do full sequential you need to add a 3.3 Ohm 10 Watt resistor in series to limit the current. Injectors with lower resistances like direct injection drivers cannot be used with the ECU’s.

Dead Time
Dead time is the amount of time the injector takes to open from when the injector pulse starts. This varies with battery voltage and fuel pressure. Also varies between different kinds of injectors but is usually about 1 milliseconds or less at 14 volts. This dead time needs to be accounted for with Battery Voltage Compensation. But it is tuned in when the engine is mapped on the Dyno or street.

Spray Patterns
Some injectors have better spray patterns and atomize the fuel better than others. Injector position can dictate what type of spray pattern is required. Cycle, Duty Cycle and Pulse Width

A fuel injector is continuously powered by battery positive. The ECU output switch to ground to turn the injector ‘on’.

Frequency: Number of complete cycles in one second, measured in Hertz. 1 Hz = 1 cycle/second. It is engine RPM / 60.

Cycle: Time from when an injector is turned ‘on’ until the next time it is turned ‘on’.

Pulse Width: The time in seconds the injector is ‘on’.

Duty Cycle: Percentage of time the injector is ‘on’ in one cycle.

Most injector ratings are to be used within 85% duty cycle. You may get more fuel through with higher fuel pressure but stay within the working limits of the injector.