my discovery is playing up,it will start on lpg but there,s nothing there on the petrol side,ive put an extra gallon of petrol in but its just cranking over but when i switch over it goes pretty much straight away..its a 1997 3.9 manual anyone any ideas?

 

I'd look into the shutoff solenoid for the petrol first. Is it getting power, and is it opening when you operate the switch?

 

Also look into the petrol fuel pump.

 

Fuel pressure test time!

 

thanks guys,i think it might be petrol its running on even though ive got the switch set to gas,the 4 lights on the guage havent moved but my petrol guage has.? the gas switch is illuminated yellow set to gas but when i switch over to petrol it cuts out..

 

You need to separate the 2 systems and then diagnosis the petrol part only.
So you need to run it out of "gas" as you call it and then you know that has zero effect on the engine, even if it is leaking.
Then you can do a fuel pressure test on the "petrol" pump as you call it and see if it is working.
Here in the US no one has the LPG conversion and we call "petrol" gasoline, gas for short.