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injector curve crosses the x-axis as well as the slope of the curve during low-
load conditions
Injector offset is not the same thing as injector on-time because of the non-
linearity of the injector right after it has opened. The non-linearity is
significant for the first 2ms, which is one of the reasons mass produced
vehicles never have higher capacity injectors than absolutely necessary. (With
a higher capacity injector, the total on-time would decrease, and more of the
on-time would be spent in the non-linear territory, resulting in unpredictable
emissions etc.)
Since NIRA i7x is a fully sequential system, the on-time per injector is double
that of a system that’s not fully sequential. The result is that you can use
larger injectors and the injectors will still spend most of their time in the linear
territory.
If you are guessing as to what the injector offset values should be and you’re
off, you may notice problems with lambda drifting with the intake
temperature during low-load conditions. If the offset is far off you will have
problems starting the engine. Two tenths (0.2) of a millisecond is considered
a large error.
When using the Wizard in NIRA rk, look at the graph (F5) for “typical injector”
and you will notice how the offset changes significantly based on the injector
supply voltage (battery voltage). It’s easy to understand that 0.2 milliseconds
will result in a lambda change of several percent at idle since the total
injector on-time may only be around 2ms at idle.
As stated above, the problem is more pronounced if you are using a semi-
sequential setup. If you don’t have access to the offset values or can’t
measure them yourself, it’s recommended that you use a type of injector for
which NIRA has already determined the offset. The Wizard lists the pre-
measured injector types. Otherwise, choose ”typical injector” in the Wizard.
This gets you a base mapping you can use as a starting point for many high-
resistance injectors and many low-resistance injectors (using the NIRA resistor
pack mentioned above.)
Injector gain
Injector gain is the fuel injector characteristic without the offset. This value is
used to calculate the injection time based on the amount of fuel to be
injected.
NIRA i7x controls the fuel injectors based on how many milliseconds it takes
to inject exactly 1 gram of fuel with the given fuel injectors. This time is
entered in the ”Injector Gain” parameter. NIRA rk has a wizard which helps
with the calculation of injector gain.
The capacity of the injectors at a given fuel pressure and 100 % duty cycle
(i.e the injector is open all the time) and the density of the fuel. Note that
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