i have installed a number of walbro fuel pumps for evo's ranging from 03's to 05's and tunned them. i never used the install kit and never had a problem running them without the install kit. however, the first couple of times installing them, i have installed them incorrectly where the car would misfire. i just think you must have installed it wrong the first time, and when you took it apart, you must of installed it properly.