On my 2018 Silverado, 5.3L , When I go thru carwash and get underbody washed or drive on rainy wet roads, engine code for cylinder 8 misfire goes on. Have had plugs, wires, and the coil pack replaced already. Mechanic looked at it and thought it was fixed. Was fine for several months. Went thru carwash again and it set of misfire code. After it dries out, it runs fine. What if anything is under there that water could get into to cause problem?