Switchable afc preboost fueling idea
 

Ok i had an idea, dont know if it has been done before, or even if it will work - but here it is!

Why adjust afc to overfuel preboost and blow smoke on takeoff all the time when you could make a system to turn it on and off when its not convenient (smog cops behind you, emmisions testing, etc)

heres how to make it: (see attachment for diagram)

tee off the afc senseing line off the manifold, run one line to the vent port of an electric three way solenoid valve (an international/navistar pneumatic fan clutch control valve has three ports and should work) run the other line to a airbrake one way check valve connected to a small pipe. (the pipe will be the boost press acumulator like a small air tank) run another line out of the accumulator (no one way valve) to the supply port of the solenoid valve. now run a line from the remaining port on the solenoid valve to the port on the afc. install a fused switch powered by ignition voltage in the dash and run it to the valve.

heres how i think it will work:

when you flip the switch on, when boost pressure occurs it flows from the manifold line to the one way check valve and accumulator then to the afc. when boost drops, the accumulator holds pressure and the afc still sees boost pressure and fuels accordingly untill you turn the switch off. if the accumulator leaks down, another boost event should recharge it.

when you turn the switch off (or turn ignition off) afc returns to relaxed no boost position boost pressure flows to and from the afc normally and it operates as its supposed to and limits preboost fueling untill it sees boost pressure.

now you dont have to adjust the afc, and can make it not smoke if you dont want it too all the time.

anyone think this will/wont work or have any other ideas? (flamesuit on):ouch:

Most guys do something in reverse of this; called a vallet switch. Keeps the truck substantially under fueled and other people that may end up in your driver seat from rippin on your truck. Your idea would work, but a 3 way switch is 1, expensive and 2, you'd end up with the AFC in a defueled condition or full fuel condition when using accumulated
Boost, no in-between. The switched reference from the accumulator would destroy any tuning you've ever done to get a low to no smoke take off but still having enough fuel to reduce turbo lag. Your system would work, but rather than using mechanical means of tuning (turning the star wheel or switching springs) the use of a regulator would be needed to adjust AFC arm position on take off instead, adding to expense and complexity. Ontop of running a valet switch to cut back fuel for said conditions. Only practical use would be running the regulator with a pressure gauge inside of your cab for on the fly AFC control.


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i may be out in left field, (afterall i havent made the thing and ive been up all night : ) but if you plumbed a three way valve the right way it should allow you to bypass the accumulator in the off position. feel free to doodle on my diagram and post it and show me where im wrong its totally possible i missed somthing obvious. i dont know how to draw an air diagram properly i winged it so my symbols may be wrong

the fan valve im thinking of is for an engine fan on international trucks and is set up with three ports so you can run both fan types (air to engage or air to release clutch) i think there in the $20-$40 range.

heres a fan solenoid example