Injector woes

[herman07]

Took the 2003 Excursion to shop for egr delete and some other ellective/preventative mods. Truck seemed to run pretty good with an intermitent miss in very cold temps.

Mech ran a scan and turned up bad injectors on 5 and 7. Also threw an egr code and a turbo code.

Then he did egr delete, new oil cooler w/hpop screen, clean turbo (it was badly coked and siezed), fuel pressure regulator upgrade (blue spring), coolant filter, flush/fill with elc, and replaced injectors 5 and 7.

Got it put back together and ran another scan to clear any codes and injector 4 failed both tests.

Anybody know why 4 would pass before mods and fail after? Is there anything else that might be causing the code. Mech said he rechecked connections after the scan and found the connector/pins on the injector and harness to be fine. Is this injector really bad too?

Thanks
JRH