How about no MAF or MAP?

[Tony Bryant]

> From:          "Josh Karnes" <joshk at tanisys.com>

> I don't have to meet any emmissions tailpipe tests or whatever here 
> in Austin either, so I am very much interested in ditching the AFM in 
> my car.  I assume that after a certain number of rpms, the ECU takes 
> over for the miixture curve.  It has to sense this rpm somewhere, 
> right?  Which means that there must be some circuitry in there for 
> determining injector pulse width based on rpm.  This must also be 
> independent of the throttle position.

Not at all independent. The figure you need is the actual volumetric 
efficiency, which is clearly a function of both RPM, and Throttle Pos.
The required pulse length is proportional to the volumetric efficiency.

> Is it feasible that you could feed the AFM inputs on the ECU with the 
> output of some circuit comprising of a frequency-to-voltage converter 
> and some op amps, so you could simulate a condition of the variable 
> resistor AFM?  Basically a voltage is applied to the rail of the AFM, 
> then there is some resistance, so there is an output voltage after 
> the drop through the resistor (there must be a reference resistor in 
> the ECU, I guess).  So, with a frequency-to-voltage converter 
> sampling pulses from the coil, you can convert the rpms to a voltage. 
>  You can then use some sort of variable resistor to find the throttle 
> position.  Use these to drive the input of an op amp that can be 
> tuned to give a voltage output approximating that of the AFM in the 
> same scenario.  This would adjust the pulse width of the injectors 
> based both on throttle position and on rpm.  No restriction from the 
> AFM either.

Arrrrggggh. Analog stuff! Stay away :-). Why not use a micro? So much 
more flexible and not at all expensive. I certainly would not 
consider a purely analog control system in my car!

Good luck with your op-amps :-)
 
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* "Insanity is the only sane response to an insane world" *
*                 >> bryantt at fp.co.nz <<                  *
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