First of all, please don't confuse or mix up points on this thread with points on my other current thread, at least for the time being I consider them different subjects. I definitely want to get my rev counter working properly (my other thread) soon. But at the moment the points I make on this thread are more 'testing the water', see what suggestions people come up with, maybe get around to building it when I have a bit more time. This is my other thread... https://forum.allaboutcircuits.com/...le-points-style-ignition.201610/#post-1918877
Background / Intro - I convert vehicles to run on LPG (propane) for a living. Most modern vehicle LPG systems use electronically pulsed gas vapour injectors driven by a dedicated mappable ECU which gets its own input from the original vehicle ECU's output to petrol injectors (the petrol injectors are disconnected and a dummy load connected when the vehicle is running on LPG). We can convert older engines that run on carburettors using older technology LPG mixer systems (think carburettor but for LPG instead of petrol) but it would be nice to be able to fit an electronically pulsed LPG injection system on older carb equipped engines. The problems against fitting a modern LPG system on a carb engine are that obviously there is no petrol ECU outputting pulses to petrol injectors to use as input for a modern LPG system, and there are no engine position sensors such as crankshaft position sensor (which could be used to drive a full group injection system that pulses all or half of the LPG injectors all at once) or camshaft position sensor (used by modern EFI systems to know which part of the 4 stroke cycle an engine is in, necessary for sequential fuel injection that fires each individual fuel injector at the opportune moment just before it's corresponding engine inlet valve opens)..
However, engines with a spark distributor do still have such cam sensor position 'output' in a way, because the rotor arm inside the distributor always points to the output terminal and spark plug wire of the cylinder that is about to fire. Almost the exact position of the engine (and at least close enough for intents and purposes of firing LPG vapour injectors as corresponding engine inlet valves are about to open) can be known by electronics reading spark plug firing moment using inductive pickups on spark plugs wires. So what I would like to do is build a system that has an inductive pickup on each spark plug wire... The system would see the induced voltage from a particular spark plug wire and output an 'injection pulse' for the cylinder whose inlet valve is just about to open when this spark fires (which won't be the same engine cylinder). The pulse length of the 'injection pulse' needs to be short (say 2.5ms) for low engine loads (say 0.25 bar absolute manifold pressure on over-run) and increasingly longer for higher engine loads up to the manifold being the same as atmospheric pressure (say 14ms for 1 bar absolute manifold pressure)....
So I have just described a system that uses an inductive pickup on every plug wire (8 pickups on a V8 engine) and a manifold pressure sensor as inputs (9 inputs) and has 8 outputs.. The 8 outputs have pulse output, the respective output pulses start when respective inducted input pulse starts and the length of each pulse is dependent on the MAP sensor input. I fully realise that this would not be a viable fuel injection system as I have so far described it, because I haven't mentioned how fuelling would be adjusted (mapped using some sort of table with rpm and manifold pressure on the axis and length of pulse in the cells)... But for my intents and purposes the system would not need to be mappable because the LPG system ECU that this system would drive (using those 8 outputs) has it's own mapping ability, the LPG ECU takes the input pulse length and multiplies it using user entered table data to arrive on pulse length for the LPG injectors. So this system plus the usual LPG ECU system would make for a full standalone mappable sequential port injection LPG vapour injection sysem on a carb engine that has an old-skool type sparks distributor but it would be 'open loop' (not adjust fuelling according to lambda / exhaust oxygen sensor inputs). The system could be improved by making it closed loop but that would mean having to make it more complicated, it would then need to be mappable itself and it would need memory to store learned 'fuel trims' data like a modern vehicle ECU does.
Any suggestions for how to go about making such setup (not the LPG side of things, just a gizmo that has 8 outputs with each output pulse beginning when it's relative spark plug fires and pulse length depending on voltage reading from a manifold pressure sensor)? Could something like a RaspberryPi / Arduino be made to do this with appropriate coding and input / output circuitry?
Background / Intro - I convert vehicles to run on LPG (propane) for a living. Most modern vehicle LPG systems use electronically pulsed gas vapour injectors driven by a dedicated mappable ECU which gets its own input from the original vehicle ECU's output to petrol injectors (the petrol injectors are disconnected and a dummy load connected when the vehicle is running on LPG). We can convert older engines that run on carburettors using older technology LPG mixer systems (think carburettor but for LPG instead of petrol) but it would be nice to be able to fit an electronically pulsed LPG injection system on older carb equipped engines. The problems against fitting a modern LPG system on a carb engine are that obviously there is no petrol ECU outputting pulses to petrol injectors to use as input for a modern LPG system, and there are no engine position sensors such as crankshaft position sensor (which could be used to drive a full group injection system that pulses all or half of the LPG injectors all at once) or camshaft position sensor (used by modern EFI systems to know which part of the 4 stroke cycle an engine is in, necessary for sequential fuel injection that fires each individual fuel injector at the opportune moment just before it's corresponding engine inlet valve opens)..
However, engines with a spark distributor do still have such cam sensor position 'output' in a way, because the rotor arm inside the distributor always points to the output terminal and spark plug wire of the cylinder that is about to fire. Almost the exact position of the engine (and at least close enough for intents and purposes of firing LPG vapour injectors as corresponding engine inlet valves are about to open) can be known by electronics reading spark plug firing moment using inductive pickups on spark plugs wires. So what I would like to do is build a system that has an inductive pickup on each spark plug wire... The system would see the induced voltage from a particular spark plug wire and output an 'injection pulse' for the cylinder whose inlet valve is just about to open when this spark fires (which won't be the same engine cylinder). The pulse length of the 'injection pulse' needs to be short (say 2.5ms) for low engine loads (say 0.25 bar absolute manifold pressure on over-run) and increasingly longer for higher engine loads up to the manifold being the same as atmospheric pressure (say 14ms for 1 bar absolute manifold pressure)....
So I have just described a system that uses an inductive pickup on every plug wire (8 pickups on a V8 engine) and a manifold pressure sensor as inputs (9 inputs) and has 8 outputs.. The 8 outputs have pulse output, the respective output pulses start when respective inducted input pulse starts and the length of each pulse is dependent on the MAP sensor input. I fully realise that this would not be a viable fuel injection system as I have so far described it, because I haven't mentioned how fuelling would be adjusted (mapped using some sort of table with rpm and manifold pressure on the axis and length of pulse in the cells)... But for my intents and purposes the system would not need to be mappable because the LPG system ECU that this system would drive (using those 8 outputs) has it's own mapping ability, the LPG ECU takes the input pulse length and multiplies it using user entered table data to arrive on pulse length for the LPG injectors. So this system plus the usual LPG ECU system would make for a full standalone mappable sequential port injection LPG vapour injection sysem on a carb engine that has an old-skool type sparks distributor but it would be 'open loop' (not adjust fuelling according to lambda / exhaust oxygen sensor inputs). The system could be improved by making it closed loop but that would mean having to make it more complicated, it would then need to be mappable itself and it would need memory to store learned 'fuel trims' data like a modern vehicle ECU does.
Any suggestions for how to go about making such setup (not the LPG side of things, just a gizmo that has 8 outputs with each output pulse beginning when it's relative spark plug fires and pulse length depending on voltage reading from a manifold pressure sensor)? Could something like a RaspberryPi / Arduino be made to do this with appropriate coding and input / output circuitry?
