[rdhzrd]

What sensor did they change? I'll check out the 1212 DTC and let you know the details of the code. The clunk or knock you are hearing may be the sound of the fuel system getting less than the desired amount. When the lift pump cannot provide enough fuel the engine can knock ( most noticable after trying to restart.) Have them perform a fuel pressure test and verify the lift pump is ok, also for a complete stall out ( possible cam position sensor ) check you oil level Powerstroke injectors rely totally on high pressure motor oil to operate. Many times this is missed and creates a lot of hunting around for problems that are as a result of the low oil level. What pressures did they come up with and did they check each head? Hope this can give you some areas to check.