Miss fire

The same problem happened to me and after several shops looked at it my brother found out that this engine rollers loose the oil pressure and thus the balancing bars (at top of engine heads) get out of their guide (balancing caps), try taking the front head pan and look for loossen rods, I highly recomend you to put an oil additive to tikenit a little, I did it and is working fine. (you may need to do the same for the other pan, for this you'll have to remove intake aluminum plenum

Could be the cam timing linking ? get it tested if not then it could be any sort of problem from faulty wires to battery contacts are a bit rusty causing it to not start the spark plugs thus not starting....