It very much depends what caused the weight gain..
If you've been feeding excess insulin with carbs, or you've had to maintain a higher carb intake because of the lack of ability of MDI of fine tuning.. Then a pump may help
But in truth, if you don't look at the diet side of things, to determin whether you are eating more calories in the day than your body really requires to maintain a healthy weight then the pump is going to make little difference to weight... Just means you have more stable blood glucose..
When I went on my pump 2 years ago, I had hoped that I would put on weight as I'm border line underweight, but alas no difference..
Even though some do say that they found their weight increase slightly for the first 6 months then stablised..