Haltech F10 - Manual (Page 43)

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4.6 Duty Cycles
Fuel is delivered to the engine by firing the injectors in sync with the engine, allowing fuel to
flow during the period that the injector is open. The period of time the injector is open is
called the injector pulsewidth. As rpm increases it is possible for consecutive pulses of the
injectors to meet so that the injectors are effectively never switched off. This is referred to as
100% duty cycle.
When 100% duty cycle is reached the fuel flow from the injectors has reached its maximum.
Increasing engine speed or load will result in a lean out condition.
WARN ING:
LEANING OUT AN ENGIN E WILL C AUSE DAMAGE TO THE
ENGINE IN MOST CASES.
CARE SHOULD BE TAKEN THAT THE ENGIN E CANNOT REV
ABOVE THE POINT WHEN 100% DUTY CYC LE IS REACHED AS
THERE IS A DANGER THAT DAMAGE WILL BE C AUSED TO THE
ENGINE
The table and graph below show the point at which the injectors will reach 100% duty cycle.
It is not common for this to happen but the potential for damage under these circumstances is
high, so care should be taken to check this factor.
Maximum Injection Time (in milliseconds[ms]) =
(120,000 x IgnDivideBy)
(Rpm x No. Cylinders)
eg. M aximum injection time for a four cylinder, on ign/by 2 red-lining at 6000rpm is:
(120,000 x 2)/(6000 x 4) = 10,
The maximum injection time at 6000rpm on this engine is 10ms. If the injection time needs to
be greater than this, then your fuel system cannot meet the demands of the engine. You will
need to increase the fuel supply, by increasing injector size, fuel pressure, or adding extra
injectors. (Refer Appendix C Fuel Systems & Staging, 89). As a general rule of thumb,
injectors should not run beyond 85% duty cycle.