LOW-Z PWM, HIGH-Z Injectors

[mr_g]

As I was looking at the schematics v3.3, I could help noticing that pre_inj0x signals are all parallel connected to OC0 output signall (as PWM mask).

So, If I use LOW-Z injectors and PWM, then all the INJ0X outputs will PWM at the same frequency... So what if I use only INJ00-INJ03 for Low-Z and INJ05-INJ06 for let's say IAC and Boost valve... So PWM would make me problems with IAC and boost solenoid....

How does this PWM low-Z thinngy works? Is this PWM constant, so injectors would get less current? How do we calculate this PWM for lets say 2ohm injectors?

[mr_g]

OK. I think that the answer lays in source of the firmware... Output that can be PWM masked isn't pulled high strongly with ATmega... Am I correct?

[rob@vems.co.uk]

As I understand it the PWM is done in software so that this issue does not occur.
PWMing is not really the effective way to control the peak-and-hold injectors because you can't use the high voltage flyback.  LowZ injectors really deserve the Peak and Hold injector drivers that control the current in hardware.  LowZ injectors work just as well with 50W resistors though...

Rob

[GintsK]

PWMing is best way to control Low-Z injectors, but VEMS officialy didn't support high voltage flyback.
However anybody can try my solution which seems to work right even at hard loads up to 85% duty for 5 injectors (race proven):
http://www.vems.co.uk/forum/index.php?topic=189.0

I have 2L turbo project using 4x 1600cc. For first I try it with 30V TVS diode and  resistors from webshop. Idle was rough and no way run leaner than 0.85 at idle. Then I switch to PWMing and external high voltage flyback (you can try PWMing with same TVS diode at idle - it easily survive such low load). Results are fairly reasonable - idling at 1.0.

Gints