Haltech F9A - Manual (Page 73)

72
exceed 85% duty cycle injection on time, and that at high rpm, injector dead time can
consume a significant amount of available injection time.
If you find that your injector flow is insufficient, you can change to larger injectors, add extra
injectors, or increase fuel pressure. Raising fuel pressure to increase injector flow rate is not
recommended if the desired flow is more than 20% than the system currently achieves. Fuel
flow is not in direct proportion to fuel pressure. Increasing fuel pressure will increase injector
dead time and reduce the flow rate of the pump.
C.3 Injector Staging
Another way of increasing injector flow, without compromising good driveability and fuel
economy is to employ staged injection. Injector staging allows the use of primary and
secondary injectors and is usually only used on high boost turbo or supercharged engines. The
ECU will fire only the primary set of injectors until a preset load point, where the ECU will
control both primary and secondary injectors.
The turn on point for the secondary injectors depends on injector size and engine
performance, but will usually occur just after the engine has reached atmospheric pressure.
Typically bar number 14 to 16 will work well in most applications. The staging point must
occur before the primary injectors have reached 100% duty cycle. Go to the highest speed
range in the fuel map that the engine is using, and make sure that the last bar for primary
injection is not too high. If it is, you must stage at a lower pressure. (Refer to the section on
duty cycles in Chapter 4).
Adjust the bars around the staging point with extreme care to ensure that the engine does not
lean out as the secondary injectors come in. When the Haltech ECU begins to stage it begins
firing both sets of injectors at once and fires them with the same duration. This means that if
both primary and secondary injectors are of the same flow rate then the first staged bar should
theoretically be slightly more than half that of the last unstaged bar. Allow a safety margin by
using 60% of the last bar.