Col, just realised it's you on the 'melted iridium plug' thread, on that thread I don't think I knew the plugs were in a Bongo V6.
Unusual aspects indeed...
Mazda's are known for switching injection methodology from sequential (during most driving conditions) to group injection during acceleration (or at least resembling group injection for the most part). But the Bongo I just converted was different again...
When the engine is started from cold it seems to run a fuelling strategy close to sequential injection, but when warm it seems to run a fuelling strategy resembling TBI (but discrete TBI for each engine cylinder). I draw the comparison with TBI (throttle body injection) because TBI systems vary both pulse length and frequency of injection pulses. Group injection would have 2 injection pulses per intake cycle which is different to the 'variable' frequency I suspect on these engines.
I could have put an oscilloscope on the engine to check the TBI theory but I didn't need to because i kind of side-stepped the issue. I fitted very quick reacting injectors and an LPG ECU that would follow the varying pulse frequency/duration/strategy of the petrol system exactly. By careful selection of nozzle size and pressure (combination on the side of low flow) coupled with the fast injectors and an unusual shape map, regardless of the frequency or pulse length of petrol injectors the LPG system matches the petrol fuelling per individual pulse regardless of pulse frequency and uses the same fuelling methodology as the petrol system without resorting to using the 'Leaning on Mazda' facility (this ECU does have a leaning on Mazda facility, as most model ECU's do, I just set up the system so I didn't need to use leaning on Mazda).
As memory serves, petrol injector pulse length never exceeds about 4ms regardless of engine load except during high load acceleration when it can suddenly jump straight from 4ms straight to 12jms... Pulse length (when below 12ms) does differ between around 2ms and 4ms and frequency also differs... But no LPG system's software allows a window on the pulse frequency. While (of course) it is the combination of pulse length and frequency that combine to create the actual amount of fuelling per engine cycle.
Your mate / installer / (or who you referred to) is thinking along the correct lines with implementing a 'Leaning on Mazda' feature.. However, the problem is that on this engine the feature would have to be used the opposite way around to on most Mazda engines on which the feature is applicable/useful. On this engine the leaning on Mazda feature would be engaged under most driving conditions and become disengaged during high load / acceleration. This implies that if you were to make use of such feature you would need to anticipate the extent/value/percentage of fuelling for the feature before doing what is usually the main part/most involved part of calibration (part load closed loop calibration) and frankly this would be a bit of a problem for someone without that kind of experience. I could do it by anticipating the map shape for the engine's character/power/fuelling strategy, setting the map shape then calibrating the 12+ms high load conditions, then (since the map shape was already set something like correct) set the 'leaning on Mazda' value to mostly correct the part load conditions, then fine tune everything from this 'nearly good' point.
Exacerbating correct fuelling when using controls such as 'leaning on Mazda', especially with variable frequency injection systems, are dynamics of injecting gas in vapour form from relatively slow performing (compared to petrol injectors) gas injectors. All gas vapour injectors are slow compared to petrol injectors but some are much better than others. Injection frequency affects matters much worse with slow injectors than faster injectors.
In terms of ECU's there are probably two schools of thought.. The ideal for most modern ECUs is to follow the petrol fuelling strategy exactly, combined with fast injectors I've gone with this school of thought on my latest Bongo conversion. Most modern ECU's attempt to do this but not all can quite manage it. The other school of though would be to fit an older spec ECU that instead of trying to follow petrol strategy exactly might be more inclined to total up any inidvidual pulses (regardless of frequency) per engine cycle. Toting up pulse duration can them allow the ECU to pulse gas injectors once per engine cycle in the usual manor.
Problems you may be up against are.. The King ECU will attempt to follow the pulse frequency but not quite manage it, while on the other hand it won't tote up pulse duration per engine cycle (as an older AEB based ECU might) either. If the ECU could follow pulse frequency, without re-reading to know what injectors you have fitted I don't know how injectors you have would handle frequency / with a 'toting up' ECU choice of injectors wouldn't be critical on this engine. Another exacerbating point is rpm feed - due to shifting injection frequency rpm detection from petrol injectors isn't a reliable indicator of actual rpm but on this engine the coil doesn't seem to be a good indicator of rpm either. I didn't bother (or need to bother) checking for reliable sources of rpm feed such as cam sensors on my latest Bongo install because (again) by following the petrol fuelling strategy pulse per pulse I sidestepped the issue... But a 'totiing up' (pulse duration per engine duration or per 2 engine rotation, i.e older LPG ECU) install would need an accurate RPM source.
What I can tell you is that the Bongo I just converted using modern LPG components, and aiming for a 'no compromise / technically correct' install (in that the LPG system follows petrol strategy exactly) install took me longer to calibrate and was more messing about than setting up the latest Valvetronic BMW I just converted. On this Valvetronic I used much the same components as on the last Valvetronic I converted but fitted smaller injector nozzles supplied at higher pressure with a different vacuum compensation model and allowed for the few firmware / software changes compared to the Valvetronic engine I did the main part of the write-up on in this thread http://www.lpgforum.co.uk/viewtopic.php?f=27&t=14183
. The changes I made for this model are pretty much purely technical, unlikely to see any real world benefits/advantages over the Valvetronic I did the feature thread on... but the changes I made are advantageous/improvements none-the-less. I've tie mention of the Valvetronic engine in on this thread because it helps draw an analogous point... Most LPG ECU's feature a 'Valvetronic' option. On some ECU's the option only makes the difference of allowing the engine to change from petrol to LPG when manifold pressure is near atmospheric pressure (when otherwise some ECU's would think the engine was running at near full full throttle and wouldn't changeover to LPG until they saw a lower manifold pressure / more vacuum). On other ECU's ticking a Valvetronic box will see the ECU attempt to adjust for the difference in working conditions between running in Valvetronic mode and running on none-Valvetronic (throttled) mode. None of the Valvetronic options on any ECU properly corrects for the difference in fuelling, which (here comes analogous bit) is the same as none of the 'Leaning on Mazda' functions properly compensates for the difference in working conditions between sequetial / group / tbi like fuelling types... Which is why I don't use either type of facility in ECUs (Valvetronic check boxes or Leanimg on Mazda sliders) but instead have developed better and less 'fudgy' ways of approaching both issues.
Incidentally, I have suggested you slot in an old spec AEB ECU to try on several occassions on thread over the years. You may find that an old ECU will tote up pinj's per engine cycle regardless pf frequency (as described above) in which case you wouldn't notice many usual aspects to your fuel system (they'd be there but the ECU by it's old-skool design just wouldn't reflect them) and you could be left with linear pinj and ginj readings which work great with just about any injectors... But won't happen with your more recent King ECU and your King ECU won't manage the 'frequencies' aspect either.