have a search round the site, there is a few cases where the car adjusts to the lpg running conditions and knocks the petrol setting out of whack. i think you will find that if you run on petrol for a while the lpg will then have problems, i think you need to have lpg set back up after running on petrol for a while. i'm sure someone will have a more definate answer for you. i dunno if the pump is the cause in this case tho as you dont mention how it was before!!