how are you powering this unit? direct from the car? or from your carpc's power controller?
second, I have found that the cable connection to my 629 is very fragile and prone to interference unless I hold the cable extremely tight. - I am using a typical 9pin din extention cable for my screen. - the stock connector comes with a very tough looking screw together type locking mechanism, which is useless when you are using an extention cable unfortunately. I am planning on heating up the garage and doing a solder job on it so permamently affix the extention cable to the units stock cables, and that should cure my 'fuzzy screen' problem.
but back to your question: check your cables, verify the proper power is getting to the unit, and since you have a liliput, you also have the "indoors" power adapter, why not bring it inside and power it up there? then at least you will be able to tell if the unit is faulty or if it is just your cabling..