I have seen this before and it has to do with the chip the car needs to read in the key . There is an rdf reader in the steering column that is shorting out and setting off the security to kill the car. it blanks out when hitting a bump and the chip in the key looses its signal and all of a sudden the security kicks in and kills the car. Something to check . Do you have more than one key for the van ? If so try a different key and see if it makes a difference. Hope this helps