Is it true you can use a 10 ohm resistor in series with a low impedence injector to be driven by the stock ecu? As long as the resistor has a high enough power dissipation rating. It sounds to me that the voltage across the injector would be too low to open it.

What are the central components in the external drivers for low z injectors? op-amps, transistors, relays, etc?

 

If you add a resistor in series with a low impedance injector, while it will seem to work, all you are really doing is turning the injector into a high impedance injector. However, you have the added benefit of forcing the injector to operate outside of it's rated environment, which will skew the operation and lead to unpredictable results, especially at low pulse width values.

All that is required for low impedance injector operation is the capability to control the current through the injector, typically up to around 6A. Optionally, you can also modulate the current in a "peak and hold" pattern to optimize the operation of both the electronics and the injector.

You need a good solid driver to handle the current and associated "smart" circuitry to control it properly. It's not a mod that can easily be made to a stock ecm without some serious work.

 

are you saying that fuel flow through the low impedence injector is related to the current? If so, at what current are low impedence injectors flow rated?

Would low pulse widths (1.75-2.5ms) still be a problem if it were a 36pph low Z injector with the resistor? please convice me that the resistor is not the way to go (unless it is ok).

 

Learning about the electrical properties of inductors on a bulletin board strikes me as
a fairly daunting task. One might start by doing some background reading. A good
general discussion of injector electro-mechanical properties is given here:

http://www.wellsmfgcorp.com/counterp...v5_i1_2001.pdf
http://www.wellsmfgcorp.com/counterp...v5_i2_2001.pdf

Some exerimental data and discussion were presented here:

http://www.turbobuicks.com/forums/sh...9&page=1&pp=15

For details of inductance, current, time, and voltage relationships you might be further
ahead by consulting a good EE text, IMHO.

HTH

 

Attempt to prove my literacy:

I've taken a couple of electronics courses, so I understand AT LEAST the basics of inductance. V=L di/dt --->responseV~e^(-t/T). I just thought the time constant of fuel injectors was so small (on the order of uSec) it was negligable even in the 1.75-2.5ms opening time range. Well, I guess it begins to become a problem at this range, but nothing too troublesome. I do all the tuning for my brother's 383 LT4 and 1.75msec PW at idle are not a problem with his FMS 42pph injectors.

Conclusions after reading the articles:

The figures at the end of the second article show .75mSec on times, and 100uSec voltage spike decay time. thats like 13% error at .75ms, which is not impossible to tune around. So around 2msPW it would be 5% error (easily compensated). The last article explains why my lt1 injectors are capable of supporting my twin turbo motor at 97-100% duty cycle with 12.5:1 AFR.

I see how sending a high frequency pulse (shorter than time constant) to the lowZ will hold it open while controling current draw.

Questions Remaining:

Does this mean you have the choice to limit the current by:
-taking advantage of inductive properties (quick pulsing)
or
-adding a resistor in series?

So is adding a ~10 Ohm resistor an easy conversion for the low impedence injectors? If 36pph low-z injectors were used, low PWs would be a small (5%) issue, right? wrong?

Have I missed the boat? Or have I joined the crew? haha.

 

If you place resistors in series with the injectors, you are not going to idle it. Injectors need energy to open. The resistor will reduce the power (and hence, energy) from what needs to be about 12 watts peak to only 2.5 watts peak. If you're going to run low-z injectors, you need a proper peak-hold driver. PERIOD

 

after a few hours more research... I realized that you need the high current initially to open the injectors, then the lower current just holds them open. so a driver that does this is needed. I now agree. Thanks for convincing me.

 

Very good info. I bet a few in the DIY PROM board would be interested in reading those articles. The turbobuicks.com info was excellent.