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Boost control and fuel / ignition map change from a rotary switch


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Perhaps to start with how I think that boost control by potentiometer works, as if I have this wrong most of what I have written below is useless:

- connect potentiometer to provide 0-5V to AN Volt 4 (I will use 4 - I realise it can be any AN Volt input). Setup as a 0-5V input
- set up boost target in closed loop at 0V through 5V (on Y axis) at desired boost levels
- turning the potentiometer changes the target boost setting.

If I've got this right, my idea for comment is below. My goal is to have position 1-3 on a rotary switch as low/mid/high boost on 98RON, with position 4-6 as low/mid/high boost on E85. I think I can do this with a single switch (and more importantly, a single input - I have a Storm):

1) I plan to use a rotary switch with a voltage divider, so that there are defined (known) steps to the boost target on the Y axis - eg position 1 is low boost (0V), position 2 is medium boost (1V), position 3 is high boost (2V), then...

2) have a Virtual Auxiliary Output which switches when AN Volt 4 is > a threshold (ie the midpoint - 2.5V)

3) switch to a second boost map using the Virtual Aux Output when AN Volt 4 > 2.5V, and repeat the table with position 4 / low (3V), position 5 / medium (4V), position 6 / high (5V). I'm not sure its critical to have this on two maps, but it feels ... tidier ... given the below

4) switch to the ignition map #2 and fuel map #2 for E85 when AN Volt 4 > 2.5V, using the Virtual Auxiliary Output 

Would this work? I have tried it in PC Link and it looks like I can make settings to accomplish the above. Note: I plan to measure the voltage output from the rotary switch - to be precise. 

Of course I'll need new injectors and to confirm my fuel system works with E85, etc etc, but I am more focused on the possibility of using the Virtual Auxiliary Outputs and defined steps on the switch as a way of creating a 'mode' switch. For example, I could have position 1 as low boost and no motorsport features.

Supplementary dumb questions:

a) I see fault settings under the analog inputs. It looks like a fault is triggered if 0V or >=5V is supplied into an AN Volt channel. Will this cause problems with my plan?

B) Wiring up a 'normal' SPST toggle switch to a DI (eg to turn on logging), switching to ground, what should the settings be?

Function = GP Input
Switch type = Toggle
Pull up = ON
On Level = Low
Active edge = [falling?] 

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For what I've suggested above, it occurs to me I could also have a 3 position switch and a toggle that switched a resistor from between pole 1 of the rotary switch and 5V to between pole 3 and ground. I might prefer it that way (Toggle for fuel, rotary switch for boost). Yes ... It's a lot of effort to save an input.

Extra question - should the ground for the switch be sensor ground in the ECU, or is grounding to the chassis ok?

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  • 1 month later...

Minor update to say thanks - the above gave me enough confidence to spend the time making the rotary switch.

I used 1k ohm resistors between positions and I think a 510 ohm one between each of pole 1 and 5V and pole 6 and ground. This had the effect of making the switch go in steps from about 0.45V to 4.54V (avoiding any error issue).

It then works just like I hoped (at least on the bench/in PCLink - I am a long way from having it going in a car...) for switching between 3 boost levels on each of two boost maps, with boost, fuel and ignition table #2 all switching when the switch went from position 3 to position 4.

Can see how this would be pretty useful as a 'mode' dial with enough creativity and virtual auxiliary inputs.

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