Injector resistor question (less resistor with higher resistance injectors)

[the_mork]

I am in many ways an electrical noob however would it be beneficial (and not terribly complicated) to replace my injector resistor pack with lighter resistors? I'm trying to get my Bosch 1600s to idle and while I'm getting pretty close with e85 I think a smaller deadtime would be awfully helpful for pump gas.

Bosch injectors are 5ohm
Stock injectors are 3ohm
Stock resistors are ?ohm
New resistor ?ohm

Would I be in any danger of damaging the injector drivers? Like I mentioned I'm an electrical noob but it seems like resistance is resistance wherever it is in line so as long as total resistance remains the same things should be okay right?

 

[Ceddy]

Deadtime is mostly caused by mechanical not electrical characteristics.

It takes time for plunger in the injector to gain momentum and start moving.

Also you must look at the injectors impedance not resistance. Impedance also takes into account the injectors inductive properties.

I doubt changing the resistor box 1 or 2 ohms would have any significant effect.


A Voltage Regulator (FIC EasyTune) or a Peak and Hold Driver may help, but for the cost of them you might as well just buy a set of well behaving injectors.


Turning your Fuel Pressure down will make your injectors act smaller and easier to tune. (And unless you have a really heavy duty pump setup, you will run out of pump long before reaching 1600cc).

Base Pressure @30 psi would size 1600s around 1325 cc.


Edit:

If the stock Resistor Pack is 8 ohm.
Stock Injector is 3 ohm.
1600 injector is 5 ohm.

8 + 3 = 11 ohm; I = V/R = 12/11 = 1.09 amp
Voltage to injector = 3x1.09 = 3.27 volt

8 + 5 = 13 ohm; I = V/R = 12/13 = 0.92 amp
Voltage to injector = 5x0.92 = 4.6 volt

So if DeadTime is voltage dependant, you are better of with the higher ohm injectors. But have less current flow.

Someone please correct me if I'm wrong, been a while since I did any calculations.

 

[mike96]

sounds like a good opportunity to make use of the EVO8's fuel pump reduction circuit. there has been a little bit of research done on when it is active, and if i remember correctly it only runs the fuel pump through the resistor to reduce fuel pressure during idle. 95% of the work could be done right under the back seat, hardest part would be running an extra wire from the ECU to the fuel pump.

 

[the_mork]

Reducing fuel pump duty wouldn't help, I'd still be at the same pressure based on how little work the pump really needs to do to maintain my base pressure at idle. I had hoped that lowering impedance would help them run a bit faster but if not then that isn't an option to pursue. I am at stock 2g pressure so dropping that would help. I'll switch to a 1g turbo fpr and see if that helps. Eventually I'll switch to an AFRP and a larger pump worthy of feeding these injectors then I'll turn it down even more.

 

[cbrfrenzie]

The resistance of your injector + resistor pack determines the amount of current your injector driver will consume. With higher the current, the injector will open faster (more energy per unit time), however you are now running the injectors on the ragged edge of what the factory drivers can handle, which could result in failure.

From my tests, low impedance injectors (taking into account resistance and inducance) open quicker then high impedance injectors of the same size. This is WITHOUT an external resistor pack, in an low impedance application (like the new FI snomobilles for instance).

The drivers in our ECU's are designed for High impedance injectors, its just Chrystler, Honda and other import manufactures in the mid 90's had an shortage of High impedance injectors, so they retro-fitted low impedance injectors with external resistor packs.

Consensus, measure stock resistance WITH resistor pack, and make the new setup match... OR buy low impedance injectors that are known to work well, and use the factory resistor pack.

May I also suggest playing with the dead-time table in the ECU?

On a side note, you can bench test the dead-time of your injector very easily with a power supply, function generator, a few resistors and an driver. If you zip-tie a knock sensor to the injector, you can watch the knock sensor output as the injector opens and closes. From that scope shot you can clearly see the peaks and troughs indicating the plunger being fully opened and fully closed. If you look closely, you can actually see the oscillations from the plunger bouncing on its seat when it opens and closes, very cool so see.

Doing that at different applied injector voltages, you can plot dead time vs voltage to the injector, and make your dead-time table PERFECT!