Literally everything. The first unit we got had 3 fuel pressure regulator failures, 1 injector, 2 handhelds, 1 ecm and would never run right until they finnally agreed to replace it with a rebuilt unit. It never drove for more than 2 miles between all of these failures. The rebuilt unit ran for about 2 heldweeks before it's ecm crapped out followed by both injectors and another handheld. There supplied fuel supply system could also never reach the needed pressure and flow rate. This doesn't even count the numbers of hours wasted with customer service and waiting on new parts to arrive. You have been warned.