1994 honda civic check engine light is on?
 

I have 1994 honda civic dx and my check engine light is on...i took my car to pep boys to try and get some codes but they told me that they could not do anything because my engine in my car is not the original one. so now i dont know what to do. Sometimes when i turn on my car it wont turn on or it will turn on but then it dies and when i do get it to turn on my car makes some weird noises its sounds like if the car accerlerates and then decelerates and when i try driving when i push on the gas pedal it feels like it hesitates to move. I have no idea what's going on. Some people told me it might be the fuel filter, because i got my fuel injectors cleaned at walmart about 1 month ago. i need help so if any of you can give me some ideas that would be great thanks!