The Low-Z extension board provides faster injector switchoff and obsoletes powerflyback for new installs. Please see GenBoard/Manual/Flyback
This page is obsolete ! Only useful when verifying old installs.
- beside VEM's advanced (perhaps a bit overengineered) injector-opening model (SW solution)
- higher flyback voltage after injector output is deactivated helps injectors close faster for even better control
- easier tuning
- especially smooth idle is hard to achieve with big injectors especially the fuel delivery amount is different among injectors (or varies from cycle to cycle) for short pulsewidth. As a rule of thumb, 1.4 .. 1.5 msec is always difficult. Usually gets somewhat easier if idle injector pulsewidth is around 1.7 msec or higher
- smoother and more economical operation
- better result for injector-sets with poorly matched (different) injopen characteristics
See [powerflyback item in webshop]. Note: not available any longer !
GenBoard features a powerful GenBoard/Manual/Config/InjectorOpening model that makes it possible (or in some cases just easier) to tune with high-flow injectors. We call injectors high-flow when the injector flowrate in cc/min is close or higher than the cylinder displacement (in cc). Like 550cc/min injectors for 450 cc cylinders. This is common for high-power (high-RPM or high boost or both) engines. We've seen giant 1600cc/min injectors for 550cc cylinders.
The injector pulsewidth at idle and low-load can be very short, in the 600..1200 usec range. In this range, the injector-opening characteristic parameters are sensitive to good tuning. Alternative to the injector-opening parameters, almost as good effect can be reached with many-many load-bins, and much work (and strange shape VE table at very low load), but this is a very bad workaround: only makes sense to apply this method with alien ECM that has primitive injector-opening model.
Raising the flyback voltage makes the injectors close faster. This makes tuning easier. This is what the power-flyback does.
In the worst case, if injectors in the set have different opening characteristics, (this can happen, even the flowrate was measured to match perfectly at fully opened state ! often seen with Siemens injectors, but happens elsewhere too), it might happen that only very rich idle is possible (engine stumbles as you try to achieve a not-so-rich idle): pulsewidth must be tuned for the injectors with slowest opening or faster closing : naturally results in overly rich condition for injectors with faster opening or slower closing.
It's not easy to see the addon-board because of the same color. It's at the bottom of the picture, has 72 components (36 on top and 36 the bottom side): the ultra-fast black power-diodes are horizontal on the picture.
Power-flyback mounted on v3.x (actually v3.3):
- anode (+ red or yellow wire) connected to the onboard flyback rail
- cathode (- green wire) connected to EC36pin23 pad - which is connected (remember?) to injector common (switched +12V supply that goes to all injectors)
- IMPORTANT: D100 must be removed before operating with PWM-ing !. See GenBoard/Manual/PowerFlyback/RemoveD
This addon board is used instead of the "traditional" direct (min 0.61mm2) wire between same pads.
The same board can also be used outside the ECM Alubos case (beware of the "connection polarity"):
- anode (+ red or yellow wire) connected to to EC36pin23 - which (remember?) internally connected to the onboard flyback rail
- cathode (- green wire) connected to injector common (switched +12V supply that goes to all injectors)
- IMPORTANT: onboard D100 must be removed before operating with PWM-ing ! See GenBoard/Manual/PowerFlyback/RemoveD
- Power-flyback has the same advantage as the high-voltage flyback: raises flyback voltage to get the (low or high impedance) injectors close faster for superior fuel quantity control
- Since v3.3, every board is populated with low-voltage (appr. 1.5V) type onboard flyback. This was decided to allow PWM-ing (a nice and literally "cool" feature of GenBoard). PWM-ing was prohibited for the traditional onboard high-voltage flyback (configuring PWM-ing would kill the high-voltage flyback, even with high-impedance injectors: because the onboard high-voltage flyback had low current-limit).
- Powerflyback adds appr 4V to the onboard flyback voltage, therefore resulting in a significantly raised, appr 5.5V flyback voltage.
- but cheers: power-flyback allows PWM-ing (either for high-impedance or low-impedance injectors: in practice, PWM-ing only configured for low-impedance injectors ). Bares up to 12A mean/20A peak current. As a comparison, an 8cyl engine with 8 injectors flow appr. 5A mean / 8A peak flyback current (but seriously bad - too high, but less than 100% - PWM-duty DC percentage configuration can result in higher current, so some margin does not hurt!).
No disadvantage at all when PWM-ing is not configured.
As a side-effect, if PWM-ing is used, PWM duty% must be slightly raised (say, from 30% to 35%). Tiny bit higher current consumption. Very good trade for the gains (easier tuning, smooth running, better engine economy).