Haltech E6A - Manual (Page 45)

45
4.8 Duty Cycles
Fuel delivery is obtained by pulsing the injectors synchronised with the engine speed, allowing
fuel to flow during the period that the injector is open. The time whilst open is called the
injector pulsewidth. As rpm increases it is possible for pulsewidths to overlap so that the
injectors are effectively switched completely on. 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 revs brings with it the danger of an engine lean out. LEANING OUT AN ENGINE
WILL CAUSE DAMAGE TO THE ENGINE IN MOST CASES.
The tables and graph below show the point at which the injectors will reach 100% duty cycle.
Care should be taken that the engine cannot rev above the point when 100% duty cycle
is reached as there is a danger that damage will be caused to the engine. It is not common
for this to happen but the potential for damage under these circumstances is strong so care
should be taken to check this factor.
Maximum Injection Time (in milliseconds[ms]) =
(120,000 x IgnDivideBy)
(Rpm x No. Cylinders)
eg. Maximum injection time for a four cylinder, on ign/by 2 red-lining at 6000 RPM is
(120,000 x 2)/(6000 x 4) = 10,
so the absolute maximum injection time at 6000 RPM on this engine is 10 ms. 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 to Appendix D for details on how to increase fuel supply. As a
general rule of thumb, injectors should not run beyond 85% duty cycle.