Fuel injection

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My son has an '88 Bronco XLT EFI 302. Started running rough - acting as if fuel filter dirty. Changed fuel filter and upon trying to start, had a fire running up firewall. Replaced fuel line that got crispy and assumed that it leaked and caused fire. Not sure of source of spark, engine and exhaust cold. Found no other damage except to wiring conduit. That night it would start, but still running very rough and would not idle. Nest day, starter would not turn over engine but a couple of turns and then lock up. Every now and then would turn over a couple of more rounds and lock up. Pulled starter and battery and had checked - OK. Changed solenoid. Same thing. Pulled plugs and cranked. Back cylinder on driver's side spewed gas. Disengaged inertia switch and cranked some more to get rid of gas in cylinder. Spark plug wire must have been close to something grounded and after a couple of full cycles of that cylinder another fire. Looks like some damage to colored vacuum lines resulted.

Assumption - injector stuck open and was cause of initial symptoms.

Son was told that bad "O" ring on injector could cause problem. Being typical son, he ignored my comments that the "O" ring was a seal and there were no signs of leakage around the injector. I thought he should have replaced injector. I admit that I know nothing about fuel injection. He went ahead and changed "O" ring and to no suprise to me nothing changed.

Since he is more likely to heed advice from others, that is what I am asking for. Anybody out there that knows how fuel injection works care to reply?