I have a 2002 Omega Cd it has been converted to LPG approx 6 yrs ago. I have been experiencing over the last 7months problems starting the engine from cold using petrol.
I makes a put put & popping noise, backfires and even though I have my foot flat to the floor on the accelarator it still struggles to tick over. When driving on petrol there is a complete lack of power even with foot down there is no accelation and it digs in. At 60-70 mph it surges and after that when I come to a standstill the engine rocks judders. It makes the car seem like it is being shaken, this stops when I rev to a 1000. After that ther is a lack of power, sometimes after it has been at speed when it has been restarted there is now power at all. sometimes when it has been restarted it sounds like it is only running on 3 cylinders, so I turn the engine off and on again and it runs ok. Recently when on petrol there is no power but when it turns onto lpg it runs ok.
Can anyone give any suggestions as to what may be the cause?

Thanks I look forward to hearing from you.