This fuel controller is derived from the water thermo hack posted last year on the FC3S list. It basically just switches in addition resistance in series with the water thermo sensor when the boost rises above a preset level. The additional resistance causes the ECU to think that the engine is cold which in turn causes the ECU to increase the injector pulse width on the primary injectors. From what I've seen so far by watching my pulse width monitor, the primaries are utilized up to about 80% duty cycle below 3800rpm at which point the secondary injectors come on line and the primaries fall back to about 40% duty cycle. The secondary injectors also run all the way up to about 80% duty cycle but the primaries never seem to max out when the engine speed is above 3800 rpm. This is where the water thermo hack comes in. At about 7psi boost (and above 3800rpm) the additional resistance is added in series and the primary injector duty cycle starts increasing again.
The circuit for my fuel controller is shown below. The 4066 analog switch is used to short out the pot (R8) until boost reaches the preset level set by pot R4, at that point the 4066 opens and the additional series resistance is added. Adjust R4 such that the voltage at pin 3 of U1 is 3.5v which corresponds to about 7psi.
My future plans for the controller are to move my FCD onto this board (from the engine compartment) so I have access to the pre-FCD boost voltage. I'll then do 3-4 taps of additional resistance that come on as the boost progressively increases thereby giving finer control.
Check out the schematic for my next generation fuel controller with three control at three separate boost points
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