ECUTEK Injector Duty Cycle

Senna-F1

I and others seem to have run into issues with high injector duty numbers when we really shouldn't be. Ive been told this value is *calculated* based on what size injector you tell ECUTEK you have, and how much fuel is being requested. And that injector size input values into the software will alter injector duty cycle number being shown/logged.

Is duty cycle on ECUTEK *measured* (actual open vs closed time) or *calculated*, and hence, not a true indication of what the injectors are doing?

SonicVQ

The injector duty cycle is calculated, based on engine load, RPM, engine temp, etc
AND it factors in injector size, latency (injector lag in milliseconds/volt) and offset (delay in milliseconds)

What duty cycle numbers are you concerned with?

SouthArk370Z

Injector flow is calculated. The ECM knows the characteristics of the injector (see SonicVQ's comment above) and computes fuel flow based on those parameters and the signal sent to the injector. There may be an explanation in the FSM (link in my sig).

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Senna-F1

89% on e50, 94% on e65, so it will keep climbing with higher e%

But, as you have said, duty cycle is not a real measurement of injector open vs closed time. It's calculated, based on several parameters, including injector size. Therefore, if a smaller than actual injector size is entered into ECUTEK (say 650 instead of 1050), and the ECU demands a certain amount of fuel, its going to assume these smaller than actual injectors will have a higher duty cycle. Because 650's need to be open longer than 1050's. Dont ask me why someone would do this, but if this is the case, is it correct that the ECU will report a higher duty cycle than what's actually occurring?

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SonicVQ

If a smaller fuel injector is entered into ECUTek (or any aftermarket tune/setup), the calculated injector pulse width (aka duty cycle) will be increased.

Then the ECM will look at the Air/Fuel sensor to determine how accurate the calculation as it compares calculated (or target AFR) vs actual.. If it is lean, more fuel will be added, and the pulse width (aka duty cycle) will increase.

With the above in mind, the duty cycle is the duty cycle.

When using ethanol, more fuel is required for the same amount of air.

For example, when using E50, the chemically ideal (stoichiometric) requires 11.9 pounds of air for every pound of fuel, or an AFR of 11.9:1. For max power it is 10.2:1.
In the example of E85, stoichiometric is 9.7:1, and about 7-8:1 for max power.

Pump gas stoichiometric is 14.7:1, and about 12.5:1 for max power.

If the proper injector size is specified in EcuTek and your duty cycles are in the high 90s, I suspect you need to increase the flow rate of the fuel pump.

How does your ECM know the ethanol content?

turtle64b

Along these lines, doesn't Ecutek also output the injector pulse width? Could this be used in comparison with another data set of simlar characteristics to determine where the error was?

SonicVQ

The injector pulse width is the duration of how long the fuel injector is provided with power, aka "on" time. It is measured in milliseconds (ms)

Pulse width is the % of "on" time to total time. Total time is determined by engine RPM, the faster the engine speed, the less time between injector "on" pulses.

So...
Duty Cycle = fuel injector pulse width (ms) / Time between ignition events

Time between ignition events = 120 / Engine RPM

At 7,500 RPM there is 0.016 seconds or 16ms between ignition cycles.
If the calculated fuel injector pulse width is 15ms, then the pulse width is:
15/16 x 100 = 93.75%

If a small injector value was entered into EcuTEK (with a larger injector installed in the engine), it would increase the pulse width and the duty cycle.

This would increase fueling, but only up to 100% duty cycle, since the injector is open 100% of the time.

Generally, you don't want to "trick" the fueling calculations. The goal is to work with the system not against it.

I will reply to your PM later this afternoon.