I have a dual-fuel 500sel.
It has not been used for 8 monthss.
I put a battery on, it turned over once and started... On LPG.
However...after a few minutes the gas ran out...It will fire a few times when trying to start it, but it will not run

I have turned it over to run on petrol but it just will not fire. There is definately petrol there because I removed the pipe to check the flow.
Last time I used the car I noticed that there was a slight misfire on petrol but oK on gas.
I fiddled with a few wires and a relay (in the space where the engine management unit is) and it then started to run OK.. but today...nothing..
As it runs OK on gas it cant be an ignition fault, so therefore I am wondering if it is fuel metering unit..
Any thoughts please.