2001 Ford E-Series Van hesitation and misfire

In addition to my first question, the fault started when I moved to a really flooded area where I drove through some really large pools of water, so the rough engine sound and hesitation started. My mechanic instructed to check the spark plugs he noticed like 3 out of 8 were still working. So I bought the platinum autocraft spark plugs meant for my ford model. The work of the engine became finer he also serviced the nozzles. But after a day the hesitation started again. So we changed the ford pump to the exact one that came originally with my van. Fine work came again infact it was running as good as new. Later that day I was unfortunate to drive to a large pool of water then I noticed a slight rough change in the work of the engine. Just this afternoon the mechanic came by, and mere looking through the hood he said the no.1 injector has stopped working. He is scheduled to come by tomorrow to give it a full check again. Any advice-help?