I installed new injectors in my Ford econoline 1990 4,9L , the car didnīt perform well so I took the injectors out and tested them two of them were leaking I left them for a couple of hours and them I tested them again and none were leaking. What could be the problem.

 

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Dirt in the fuel is the most likely cause. There may have been build-up in the fuel rail, and removing the injectors loosened it up.