Prins problem

[iancromwell]

Hi all, I have just purchased a landrover discovery with a Prins setup on it. Underneath are three gas tanks i was told with 110litre combined capacity. Whilst running with the tanks full - no problem. After 140 miles the guage reads two green lights, some times just after going down a hill, the four green lights flash then the red light they keep flashing and the beeper sounds. It changes over to petrol and they only way to get back to gas is to stop turn off the ignition, then when you turn the ignition back on it's back to two green lights checks itsself over and runs on gas again.

Any idea whats going on????

Thanks in advance

Ian

[lpgnewbbie]

The Stag system I have switches over when the gas pressure at the regulator drops below a preset value (i.e. your out of fuel), the fuel level in the tank is immaterial as the gauge is pretty poor at telling exactly how much fuel you have left.
As you drive the tank contents will move around, alot! There are no baffles in the tanks to stop fuel movement.
I doubt very much that LPG systems have a phase separator at the tank side to prevent gas getting into the line rather than liquid, they do draw from the bottom of the tank but are not full proof. Get a big enough gas pocket at the vaporiser end and the pressure will drop as the gas will not expand nearly enough compared to liquid when heated. (Gas @10Bar to gas @1Bar 10-1 expansion. Liquid @1bar bar to gas @1bar 270-1). A drop in pressure will make the system think its out of gas and will switch back to petrol with a beep or 3 and some flashing lights.
Not sure if its recoverable without stopping and starting again, as system errors have the same result, switches over to petrol.

If you want to test the theory drive down that same hill after 140 miles or more, pull over on the steepest part and leave it running, it should swap back to petrol once the gas pocket hits the vaporiser. Turn it off wait and try and restart it, if it refuses to switch back to lpg on that incline, you are drawing gas not liquid from the tanks.

If you have the prins software and lead + a laptop you could see if the pressure is dropping.

Just a thought, I could be way off.

[rossko]

Wot he said.

Multiple tank installs can require careful investigation; for a start the level gauge is fitted to only one of them, so you really have no idea what's in the others. Certain fault conditions can cause any of the tanks to either not fill or not empty, which will affect range and capacity; in some circumstances fuel will transfer itself between tanks and cause peculiar effects.

Maybe the first step is to run the setup as dry as you can, then note the fill amount, and see if you think one tank may be disabled.

[iancromwell]

Wot he said.

Multiple tank installs can require careful investigation; for a start the level gauge is fitted to only one of them, so you really have no idea what's in the others. Certain fault conditions can cause any of the tanks to either not fill or not empty, which will affect range and capacity; in some circumstances fuel will transfer itself between tanks and cause peculiar effects.

Maybe the first step is to run the setup as dry as you can, then note the fill amount, and see if you think one tank may be disabled.

Thanks both for the info, i was advised the range should be approx 380 miles on the gas so problems after only 140 miles are worrying. I do have a waranty for 12 months parts and labour so if not filling all the tanks up I will go back to them, just a shame it's a 70 mile round trip from home.

[rossko]

You'd be lucky to get 18mpg on a petrol Disco. That should translate to about 15mpg on gas; 380 miles would need a tank capacity of 25 gallons, 115 litres, so that part is reasonable.

That would assume the tanks were full before you started of course ... it's all meaningless speculation until you know how much has gone in.

I would expect to get around 140 miles from just the two small undersill tanks.

[iancromwell]

You'd be lucky to get 18mpg on a petrol Disco. That should translate to about 15mpg on gas; 380 miles would need a tank capacity of 25 gallons, 115 litres, so that part is reasonable.

That would assume the tanks were full before you started of course ... it's all meaningless speculation until you know how much has gone in.

I would expect to get around 140 miles from just the two small undersill tanks.

Not having it long, still working out an approx mpg i think 14-18 on gas (at 18 was driving like a granny though) The setup as i have been advised :- two rear 40litre tanks in place of the petrol tank and one long 30litre tank under the sill ( drivers side) combined with a custom 7.5 gallon petrol tank if its all working it should give a reasonable distance.

[rossko]

Tankage with a 110 litre water capacity will hold only 80-90 litres of fuel, due to the 80% filling cutoff leaving an expansion gap.

[iancromwell]

Filled from empty, 67 litres and only 200 miles from full to empty. It has started to play up on starting from cold, there is no power for 1-2 minutes(running on petrol). Foot flat to the floor and only 20mph.

Going back to the garage tomorrow for investegation.

[Gilbertd]

Fuel consumption sounds about right as that is almost exactly what I get from my P38. If that was from empty though, you've got a tank that isn't filling as it should take more than that. Poor running when cold is not connected with the LPG system and don't let them tell you it is. I've had something similar where it wouldn't rev when initially started but all I did was switch off and restart. It's only ever done it the once though so I haven't investigated further.

[rossko]

Poor running when cold is not connected with the LPG system...

Careful now, it is possible for a sick gas system to teach the petrol system inappropriate trim values while running gas, that will show up the next time you run on petrol e.g. starting up next day.