Ok here is a challenge for you electronic experts.
My 88 5.7 Camaro is duel fuel it will run on either petrol or propane. Ideally I want to run on propane all the time as it is cheaper but the vapouriser cannot cope with high engine loads ie kick down above 50 mph and speeds over 100 mph. What I'm trying to do is design a circuit that will switch to petrol in these situations.
To switch to petrol all I need to do is make one wire open circuit ie a relay will do this.
My idea is to monitor the output from the throttle position sensor and the lambda sensor so for example

IF TPS>3V AND lambda output<200mV THEN open relay (switch to petrol)

I also need some hysterisis in the circuit so the relay does not at some point switch on and off rapidly. eg

to switch back to propane TPS<1V

I think I'd need to buffer the sensor signals using OP amps and measure the voltages using Zener diodes and use a transistor to operate the relay.
If anyone can design a circuit I would be most grateful.

Simon

88 Camaro 5.7 TPI