selectable tune for octane.
 

I had touched on this as a reply to someone in the OFT V3 thread and thought it might deserve its own thread.

It should be easy to have a switchable octane tune utilizing the flex fuel open source tune that is out.

I mean think about it. The flex fuel tune is based on a 0-5v source on pin 20 creating an interpolation between the a and b fueling and a and b timing maps.

It should be easy to create a little circuit with a 2 or three position switch that has a different resistor on each position that will provide an input voltage between 0-5v.

This would allow for timing and fueling differences between 91 and 93 octane. Hell by reducing timing in the lower octane map, you might even be able to have more variances for even lower octane fuel.

You could tune it for say 89 on the low side and 93 on the high side and have either steps of gradation for cali 91, better 91, 92 and 93.

This could be even more useful in other countries where they are forced to sometimes use ron95 and ron 98 but e85 isn't readily available.

I was also toying with the idea of setting it up for auto interpolation using knock signals as an input instead of a manually controlled source.

It would probably require some kind of delay in changes to avoid unnecessary knock events though.

Not sure that that part is feasible.

What do you guys think. How many of you might be interested in something like this?

Jaden

Would that be any better than the OEM knock strategy? Isn't it really doing the same thing (IAM globally reduces timing etc)? Coding in from the OEM ECU would be hard, using external knock sensing equipment would be just as awkward etc.

The rest of your idea is feasible.

built in knock correction is much more minute...
 

The built in knock correction is much more minute. This would allow for greater margin of change.

It might not be much better. For it to really be feasible we would need to implement a kind of delayed trigger of some sort or maybe a switch that will initialize an attempt to interpolate with knock sensing being a protection and stop gap when fuel changes are made.

Because you're not going to want to go straight to a 93 map if you get access to 93 say if you have a quarter tank of 91 still. of course having multiple voltage selections or a potentiometer as the voltage control would do the pretty much the same thing.


Jaden

Auto interpolating knock signals seems difficult

All you need is a swith to earth from evap pressure input. Ecu pulks pin 20 high using internal! Pull up resistor. So for badic map switch you jyst neec to provide earth or open circuit

You could use this to switch between 91\93 maps you woyld have to zero all the fuel interpolation and cranking pulse adjystments.

Or use it to switch between 91 or 93 and E85

Yeah...
 

I figured to use it for octane adjustments, you'd have to disable fuel interpolation.

I would think that would make it impossible to adjust between 91, 93 AND e85 because if you disable fueling interpolation, it won't work for e85.

Possibly you could choose a setting for 91 that is below the .5v and interpolate just a timing reduction for that, but then I would think that it would throw off the timing adjustment on the upper end for e85 since the interpolation would be shifted down on the A timing map.

Jaden

if that would be feasible, then you could add a button select switch to the arduino for it to output a specific voltage below .5 like say .35 if the switch is selected and the E% is below 15 or 20 and then write the bin to reduce timing if the voltage on the input is between .33 and .36 while adjusting everything from a higher set point on the timing maps when voltage is .5 and above.

I haven't really gotten a chance to delve into the code for the flex fuel maps enough to understand what's going on well enough to determine what's feasible with it yet.