Lambda controller "hack"

[nikwal]

Hmm I dont know if all of your celicasupras already got oxygen sensor but mine didnt , so I've been running megasquirt for two years maybe, got it running pretty well but then now i went back to original ecu with this modification to try to make my car not act like such a gas guzzler and also protect against leaking hoses and such..

http://dsl.mine.nu/lambda2.gif
,,adjustment is a bit of a beatch but not too hard with good potentiometers. It's a bit of a hack but it works surprisingly well. It connects to the Vs signal if i remember correctly now..

[cheappower82]

So did you build a circuit on a PCB? I'm not so good with electronics, but i'm guessing this is something like an s-afc

[nikwal]

Built on experimental pcb and wires, around Two TL074 op-amps with +-15Volt supply from a dcdc converter i found in my drawer..

I'm thinking now that some +supplys to the potentiometers on schematic maybe should go to Vc signal.. hmm well , it works OK otherwise too
Pot values doesnt really matter,, but multiturn pots are recommended..
..Also I guess it wouldnt be too hard to convert wot'detection to throttle position sensor if one wants that ,but i'm too lazy for that..
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Maybe I should try to explain what the hell I did..
O2 signal from sensor is compared to preset voltages(target pot's usually 0.8 and 0.5volt or something like that), either high for idle or low for cruise..
If o2 voltage is higher than preset voltage output on comparator is positive and starts to charge the capacitor, value of that pot is selected so that it's possible to smooth out o2 sensor's operation (The voltage should remain at ~0.76 to 0.8 volts at idle and not dip towards 0volt and up again, then the time is to short..
Then signal goes in to a buffer so that the amount of correction can be set after without affecting the time.. I'ts important that the 2k pot is low compare to the resistors after(390k) otherwise it will lean or rich towards wot. Maybe a 1kpot would work even better.
Then there are two comparators that disconnect the correction by earthing the capacitor while you are accelerating hard and when using engine brake,resetting capacitor value so that ecu will not be fooled..
Then there are one opamp(upper middle) that alter the target value at idle, otherwise it'll idle like a piece of crap..
Dont set time pot at zero or high current might destroy the opamp(that's why the 10ohm resistor is placed in series with mosfet.. )
Any enhancement mode mosfet can be used, I used IRF740 only because that's what I've got in my drawer.. Oh and I put in a slow start too, Not sure where it's supposed to be but i think that It should work where it's put.. It works best with heated sensors, or you should have a massive slow start..
I mean for my everyday home to work and back supra It works good considering It cost almost nothing to build , the hardest part to find cheap or for free is the + - supply dcdc for the opamps..
In the past it's happened that I've been driving for weeks with a cracked air hose somewhere, now it doesnt really matter very much, as long as it's not on wot.. It'll be compensated most of the time now if it isnt REALLY bad like the hose is gone or something..