MS controlled WI idea
 

OK I had an idea about how to get the MS to control WI based on injector flow without using a HSV. So I googled around a bit and it seems that this idea has already been applied.

Basically you use the fuel injector signal as the pulse width modulation for the DC motor for the WI. The injector signal is not strong enough to power the motor from what I can tell. But one could use an amplifier to boost the power of the signal so it can power the motor. Thus, as fuel injection increases, water injection increases proportionally via PWM.

Now you would not want WI to run all of the time, so one could use the WI control capability of the MS to arm the WI system based on a boost threshold (this could also be done with a simple boost pressure switch, but would not be programmable like with the MS). The MS would arm the system directly (power on the amplifier through a relay for example), then indirectly modulate the WI proportional to the fuel injection via the amplified fuel injector signal.

So has anyone tried this? Seems like a PWM amplifier would be cheaper and more DIY than a HSV compatible with water/methanol.

But can you tune it independently of the other "injectors"?

No you would not be able to, at least not directly. The PWM would be 1:1. But perhaps the output voltage of the pulse could be varied to increase gain?

I know BTW that Devil's Own has their progressive controller for $100 but that uses MAP, not injector flow rate. The DO system would inject the same amount of water regardless of RPM as far as I can tell since it does not have a tach input if I read the description correctly.

Instead of WI volume being proportional to boost pressure (devils own controller), it would be proportional to fuel volume. Therefore at lower RPMs it would inject less water than at high RPMs. This idea would sort of emulate a 3D WI map in that your MS map is going to increase fuel flow (via injector PWM) with both boost and engine RPM, and thus the WI would follow that map. Just a matter of being able to adjust 'gain', that is the ratio of water to fuel.

edit: solution in post below

you can probably use adjustable resistor or make a very simple adjustable relay board which would basically switch from one relay to another based on input voltage and those relays along with adjustable resistor would make for a nice fine-tuning.
that way you can trigger specific output bank (relay -> resistor) on specific fuel injector pulse.

That's not a bad idea, actually.

It's how the DO controller works. They PWM the +12 supply going to the pump to vary flow. One could easily use either the MS's injector outputs or the dedicated WI output (all of which are open-collector) to drive an external MOSFET which would do the same thing.

I wonder if the frequency (or rather the range of frequencies) which the injector drivers run at is similar to the frequency at which the DO driver runs the pump... I guess I can figure that out pretty easily.

The bigger question for me is whether one method (pump PWM vs. HSV) produces better results- linearity of control, spray pattern at nozzle, etc... That I'm not sure how to test, since I don't have an HSV.

Sorry about that, I edited my post (for clarity) while you guys were responding :)

Yep the DO controller uses PWM to control the motor to regulate flow. Linearities are a concern I agree, not sure about that. For example, how linear is flow versus pressure for the WI nozzle?

I did look at some pumps on the site that makes the DO pumps. Not sure if it was exactly the same model, but it was a 12V 150 psi pump. The current draw was about 10A, so about 120W would do it, not too bad. 10A is what is listed on the DO site as well for the progressive controller.

Good stuff, I should try that.