I find Transit petrol ECUs continue to receive actual lambda while running on LPG, you reckon actual lambda is disconnected from petrol ECU when running on LPG (you refer to the diversion). Does your diversion disconnect lambda from the LPG ECU while running on petrol? Due to the same point as above (i.e. no need for emulation while running open loop), if the petrol ECU is disconnected from actual lambda while running on LPG it begs the question why.. Can only think of a couple of reasons why ths should be so and I've never known them to be so on Transits. Reasons would be the petrol ECU holding lambda at a certain voltage, perhaps during engine warm-up or limp home type conditions (again not seen this on Transits), or the combined rpm module / lambda electronics on your Transit is more similar to the type of units fitted on Vauxhalls (which do need to disconnect actual lambda from the petrol ECU while running on LPG so emulated lambda can be fed to petrol ECU).
I didn't find signal at ecu, yes, yes, don't know
Have you got pin details for petrol ecu/O2 input at the ecu, I could not find a matching signal with one DMM on O2 sensor and one DMM for probing, if I get time to setup scope next weekend I should be able to compare signals and see if I've missed the plot. I did mention a possibility of an additional, possible parallel, connection in the loom, didn't find one by probing, might show an error in my methodology of recording results, or it maybe just an unsuitable comparison method altogether.
When repairing both Vauxhalls and Transits I used to connect a multimeter directly to actual lambda voltage, I still do that on Vauxhalls but for a long time now when repairing transits I haven't bothered, as I've found actual lambda can be read via live data method. Both Transits and Vauxhalls will switch back to petrol (due to LPG system having detected a fault) after several seconds of receiving none flicking lambda signal. On factory systems with distributor unit the usual cause of none flicking lambda is either a problem with the reducer (pressure, flow or leaking diaphragm issue) or a problem with the distributor unit (usually plunger or stepper issue)... So, when I see a system that will at least switch to LPG at all (perhaps necessitating multiple engine starts or battery disconnection for a while) and I read lambda voltage (via OBD and/or at the probe itself) at 0v while running on LPG I assume lack of gas flow to the engine causing actual lean mixture, then go on to check the reducer / distributor. Only if the system wouldn't switch to LPG for a period of less than say five seconds would I suspect the rpm module (or other electronics in it). I recognise that if your unit switches lambda between petrol and LPG ECUs there is the potential for shorting lambda to ground but I've sorted maybe 50+-transits and only ever replaced 2 rpm units, the others had problems with reducer, distributor, EGR etc. If you've only fixed 3 Transits and all 3 due to rpm module faults, don't know what's going on there! Problems running on LPG and lambda reading at 0v you say...?
Never claimed to have only fixed 3 Transits, just the 238002-050 modules.
Numerous other members here and on the Transit forum have had problems attributed to these units. You've replaced 2 modules in 50 repairs, that equates to a 4% failure rate, it might not be high up on the check list for ongoing problems, but, for the intermittent problems and poor fuel consumption I was experiencing(see post) it was the solution.
I'm not so sure there is a ground(as in vehicle, battery, body) in the related wiring to short out to, there are obviously return path wires to the ecu's, referred to these previously as 0v from the external(to the ecu) components, probed potential differences between these and vehicle ground.
As you rightly point out, there could be X number of other reasons for problems with Transit lpg system, but here I'm only dealing with what I've found regarding the combined RPM and Lambda Transit module, and not the Vauxhall unit which is a different kettle of fish. Please read from multiple previous posts in case you missed it.
There are several versions of the Necam filter 238002, for lpg integration into various manufacturers(Vauxhall, Subaru..._)
I have no knowledge/experience of these what so ever, only the 238002-050 for the Transit.
Anyway, for those who wish to "play" around for themselves, if you HAVE unexplained intermittent problems and poor fuel consumption it's worth swapping out for a known good one even just to test and confirm, I'd rather spend 15 minutes trying this than spend hours checking, testing and monitoring other parts of the system.