Nistune Forums

Hey Guys,

Does anyone know anything about how the ecu calculates when to change from group to simultaneous injection mode?

Is it calculating this all the time depending on pulse width or is it a fixed value?

I'm guessing Matt could check this on the bench rather easily, if not already known?

Once you go to bigger injectors it should theoretically not change over until a higher engine power point if it’s actively calculating the value all the time due to the shorter pulse width.

Likewise if its fixed value, it would be nice to know its location to optimize the changeover point.

I'm thinking it can't be fixed or else people would be having more trouble with smooth running when changing injectors etc then there is?

Thanks

According to the Z31 FSM: "When any of the following conditions are met, fuel injection shifts to simultaneous injection from group injection.

*Engine speed is more that 3,000rpm.
*Injection pulse duration is more than 6.5ms
*Cylinder head temperature is below 60 degrees C (140 F)

This is what my manual says

The control unit will shift fuel injection timing control from "group" to "simultaneous" under the following conditions:-

a. Cranking the engine
b. When engine speed (rpm) multiplied by the group injection pulse width (ms) is greater than a constant (k) programmed into the ECCS unit

so "rpm" x "ms" = greater then set "k" value then simultaneous mode selected

(rpm is a live value changing all the time)

(ms is a realtime value but can it calculate the real ms value or just derive what it thinks it is from the k multiplier and tp scale?)

wonder where is this "k" value is and its value.

i was just fiddling, using the following as a rough guide with dummy values only for an example.


3000rpm x 7ms = 21000
6000rpm x 3.5ms = 21000

k= 21000 in this example

so lets say you double your injector size, so the pulsewidth (ms) halves

it now looks like

3000rpm x 3.5ms = 10500
6000rpm x 1.75ms = 10500

so if the "k" value remains the same

it will not change to simultaneous mode until the engine makes alot more power, unless there is a fixed rpm value that auto switches it regardless of the calculated value from the above formula.

in theory, thinking about it, the "k" should not need changing, as the real world time available will not change before the injection overlap.

provided it calculates the (ms) value correct, which i assume it can, even if your k multiplier was higher and the tp scale lower or, lower k multiplier and tp scale higher, it still equals the same realworld pulsewidth and same air fuel ratio, it should calulate the correct "ms" value under all conditions.

so it should all be sweet in theory.

If you double your injector size wont you be also changing the k value?