LPG Discussion Forum

Had a phone call yesterday from a former neighbour who has just bought a new car. It's a 5.7 Hemi Dodge Ram pickup with LPG. His question was pretty basic, how does he use it and how does he fill it up? The dealer he bought it from took it in as a part ex and normally deal in diesels so know nothing about LPG. He's never owned anything on LPG but know I did so could he nip round and show him what he needs to know.

The switch is one of these https://lpgshop.co.uk/prins-vsi-switch- ... 1-7-wires/ and the reducer is a Prins so I suspect it is a Prins VSI on it. Couldn't see the injectors as they are under the plastic engine cover but assume them to be Prins (or Heihin) too. The switch was showing one LED (bottom right) but poking the button and the LED stayed on but 3 of the green LEDs came on too. Started the engine, poked the button and the bottom right LED went out, the three greens stayed on and a quick sniff of the exhaust told me it was running on gas. We switched the engine off, restarted a couple of minutes later and it did the same so it appears to be changing over automatically. Eventually found where the filler had been hidden and explained to him how to fill it and downloaded the autogas app on his phone so he could find where to fill it too.

However, as he was leaving, he started the engine, 3 green LEDs showing, bottom right one went out but then the switch gave a single beep, the 3 greens went out and the single one at bottom right came back on. Does that mean the level gauge is lying and it had only a dribble of LPG in it or is there something else we should have done? He will be passing the Pinchbeck Morrisons this evening so is going to try filling it and see how much gas it takes.....

There's VSI1 and VSI2, diagnostics for VSI2 is a closed shop because none Prins dealers can't get the software activated. Given the type of switch it's probably VSI1 and he/you could get diagnostics for that if you wanted.

The bottom right LED will be on regardless of whether it's switched to stay on petrol or to automatically switch to LPG but it's brightness will differ depending on whether it's switched to petrol or automatic mode. The level gauge doesn't appear until it's running on LPG.

Could be that the gauge is showing wrong (edit and it's really out of gas) or it could have switched back to petrol due to detecting an error situation. An example of a detected error is if the pressure reading isn't close enough to the set working pressure in software (including if pressure at idle is too high, not only too low). Worth filling the tank to see if it was just due to the gauge being faulty and the tank empty. If a Prins electronic valve saver is fitted it can be setup to switch back to petrol if the valve saver fluid runs out. Or there's the full range of usual type errors such as reducer too cold, loss of RPM signal (VSI1 may have a discrete RPM module and they can go wrong). Or it could have been set up wrong in the first place - the 5.7 Hemi can disable engine cylinders in certain situations, which causes the LPG ECU to read lack of petrol injector pulse on those cylinders, which will be interpreted as an error condition if the ECU isn't set up to not interpret such condition as an error.

Agree, I think we need to wait until he has made a complete pillock of himself by not being able to work out how to fill the tank with the help of the forecourt staff. I told him that the gauges are notoriously inaccurate anyway so he should just reset the trip when he fills up and find out how far it goes on a full tank. It seemed a bit of a coincidence that we had it idling on gas for a good 10 minutes for it to run out just as he was about to drive off. Is a single beep correct for a low pressure/ran out indication? I looked at the Prins website and that mentioned 3 beeps.

Just going on my memory I would have said Prins only gives 1 beep when the gas runs out. I could be wrong, it isn't often I run Prins systems to empty.

Prins VSI 1. 1 beep LPG off. 2 beeps LPG on , continuous beeping on empty or too low gas pressure until you switch to petrol. or fill up. you can get away with switching and switching back if the gas pressure comes back up or just got low going round a corner near empty.