Misfire

Started with misfire on number 3, I have code reader. Changed plugs, coils number 3 injector. This is the model that intake has to come off to get to coils and plugs, did that three times. Misfire moved to 4. Towed to dealer figured they had better diagnostic equipment, wrong. 3945. $15.00 later misfire is on number 2. They replaced all the parts I put in plus ECM. Told me they were going to put engine apart, really? After replacing all the electrics. I paid the bill and towed it home. They would not release it unless I paid. I contacted Nissan USA and they refused to step in, all I asked was they help the dealer because they didn't seem to know what they are doing, just throwing parts at it. Bolts were missing, clamps not on, ECM flopping around, bolt missing. Any ideas on what I should look for? I did compression check on 3 when I first started it was good.