Hello, There is a factory service bulletin that relates to engine ping. The repair is to replace the PCM, which has already been done . Some vans have egr valves- Late build, This valve needs to be checked for proper operation. There is a knock sensor that may be weak or loose. This may not set a fault code but can cause ping. The dealer should have checked this already. There are basic conditions that can cause engine ping. Engine overheating, vacuum leaks, combustion chamber deposits, ignition cross fire and of course - bad fuel or poor fuel.
Chrysler does state that spark knock-ping is considered normal under certain conditions. This may be in your owners manual. You may be able to reduce spark knock/ ping by having the cylinder combustion chambers cleaned , cooling system and EGR tested . And if you are going to climb hills use a higher octane fuel or octane additive to the fuel. And its best to not drive under conditions that cause ping, Try driving past the ping or under the ping.
Most combustion chamber cleaning procedures use chemicals added to the fuel. Which you can do yourself.
If you need clarification or more info please reply, Thanks Scott