I have a a stag lpg kit in my car but it switches over to petrol and beeps after doing about 160 170 miles. what would the issue be I don't think it's a issue with the outside temperatures . as in the winter it's been fine even in minus temperatures. it did this last year aswell a few times I'm really not sure what it is I don't think it's the filter as when I had the filter changed last time it did that aswell. any ideas the reason I know it's not the gas hasn't run out is because when I fill it up I only get between 25/27 ) litres in usually I can get 40-43 litres. when it actually runs out. it's annoying Any input or ideas appreciated thanks.