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MS - controlling LPG solenoids


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I had a search and found some info, and a few people who were going to try, but couldn't see any success stories - has anyone got MS controlling both petrol injectors and LPG solenoids via dual maps?

From what I can tell from searching:

You will need to wire up some sort of electrical switchover between the petrol injectors / LPG solenoids - to disconnect one and connect the other when you switch maps (should be fairly easy - relays powered from the LPG switch, same feed as switches the map on the MS)

The LPG solenoids are lower resistance, so you will need resistors inline to bring them up to the same as the petrol injectors.

The PWM values to make them fire are going to be different, so you will likely have to pick a middle ground between petrol and LPG and likely have to retune both.

I've got LPG via a BLOS on the 3.5 at the moment, when I go to the 4.6 I am going to have to swap to a different vaporiser anyway, so if it's 'easy' to go to multipoint via MS it makes sense to do it then - rather than swapping to a bigger single point vaporiser, then possibly running out of flow on the BLOS - tinley say they 'think' it should cope with the extra capacity but didn't sound entirely sure of it!



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The PWM value won't be different if you're using high impedance resistors, because those are time-driven, not PWM. PWM is only used for low impedance injectors (if the PWM setting is set to 25.4 or something, it's basically at 100%). Req_fuel will be the same-ish as long as you size your injectors properly.

Best IMO would be to go to low-impedance petrol injectors as well, and just use PWM. The resistors will be rather expensive.

We never got around to actually implementing it, but it was all worked out in my mind...

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I would have thought you could use metal encased high power resistors, should be a few pounds each?

Any ideas on suitable low impedance petrol injectors that will fit a thor manifold and fuel rail?

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To play devil's avocado, you could run both sets of injectors simultaneously as staged injection, not sure why you would though.

3.5 Flapper injectors are low-Z and use a resistor pack, would fit if you used the flapper fuel rail.

I'd double check your ECU has the flyback protection / current limit before going too far. I have buckets of the necessary components if you need them, I don't bother fitting them as no-one uses low-Z usually and they add a potential point of failure.

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I had big plans for this on my 90, using the peak and hold boards from jbperf.com and switching feeds over between the two sets of injectors with a relay. No need for any pwm from the MS itself, the boards do it automatically.

Unfortunately I never got around to doing it!

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  • 4 months later...
  • 3 years later...

Does somebody really implemented it already? I have a lot of thoughts about it, but not sure if I'm really ticking all the boxes..

Switching between the different injectors is easy, but the MS settings between petrol and LPG are very different. Does somebody actually has LPI working by MS?


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Not on a defender, but it's been done on other cars. MS3 has settings for injector switching for running dual fuels - different AFR targets / injector dead times etc. It runs off the same injector drivers, with relays to electrically switch the injectors, or if you have enough injector drivers onboard using 1-4 for petrol, 5-8 LPG etc..

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