re engine shampoo

Hey guys, I was wondering if you can provide some helpful info., looking to engine shampoo my 01'' Blazer with your typical engine shampoo spray then hose it down with a pressure washer. Will this do any damage to the engine? Should I leave the vehicle on or off? while spraying the engine shampoo & rinsing afterwards with the pressure washer ?
Tips ???
 
Thanks

Stay away from the distributor when power washing it is all. Also if you have a car wash nearby go there instead of using a power washer, use the hot wax cycle since that works better than cold