Low impedance injectors and resistors.

[trakkies]

On another forum, a very knowledgeable person stated quite definitively there is no advantage on a normally aspirated engine using the PWM current limiting offered in MS11 V3 - it is better to either use high impedance injectors or resistors. He further added that MS3 doesn't have the option of driving low impedance injectors directly to emphasis his point.

Since the Megamanual is pretty clear about the benefits of driving low injectors directly (unless I'm not understanding it) would others care to clarify?

[Bernard Fife]

Trakkies,

In addition to opening faster, low impedance injectors have another significant advantage when used with PWM: the PWM can be increased if the supply voltage is low (and decreased if it is high). This is especially useful when cranking (and even moreso if it's cold, etc.). You can't do that with a resistor. PWM also doesn't cost anything in additional hardware in most cases (unlike 25 Watt resistors which are about $5-$10 each for the good ones - times the number of injectors you are fortunate enough to be using). PWM is also easier to tune (just some settings in the software) - though you must tune it.

However, the resistors are sometimes simpler, don't require tuning usually (though you may find yourself buying new ones if the resistance you choose initially is too high or two low). The electronics can be simpler with resistors in some cases too.

Like everything else on a vehicle, it is a compromise between a number of factors, and anyone who doesn't see that doesn't understand fully.

The PWM option in some of the newer hardware (like MicroSquirt and the Sequencer) has current limiting in the driver chips, so it doesn't need to be done in the software. This is very different than using resistors, though.

Lance.

[trakkies]

Thanks, Lance. As a matter of interest, how do most new quality cars handle it? High impedance or low with some form of current limiting? If still using the same type of injector?

Cost of resistors wouldn't be an issue here - my car had them as part of the original EFI set up. I deleted them (and made a new loom without the wiring for them) when I built my MS - so wouldn't have been too pleased to know I'd made the wrong decision. ;-)

[2vwjones]

I am running low impedance injectors in my MS 2 3.57. they are 300cc bosch green top. I have never had any problem. I have changed from High to Low and back a few times tell i got the right fueling that i needed. Just my 2cets.

[Matt Cramer]

Thanks, Lance. As a matter of interest, how do most new quality cars handle it? High impedance or low with some form of current limiting? If still using the same type of injector?

Cost of resistors wouldn't be an issue here - my car had them as part of the original EFI set up. I deleted them (and made a new loom without the wiring for them) when I built my MS - so wouldn't have been too pleased to know I'd made the wrong decision. ;-)

Very few new cars with port injection use low impedance resistors; nearly all factory injectors these days are high impedance.

Direct injection is another story - I believe they typically use analog peak and hold control circuits, with the injectors being fed somewhere from 50 to 80 volts.