I have a 2006 MCS with 39K on that is having a hard time starting. It always starts and it usually doesn't take more than a second or two of cranking but it starts with a whimper and the RPM needle dips and occasionally yoyos for a second before leveling out either on its own or after I press the gas pedal. The car has a 15% pulley, step colder NGK plugs, RMW Bosch 550 injector that were bought second hand, and a RMW tune. On advise from Jan I swapped out the fuel pressure regulator with a used regulator I got from Way Motor Works and the problem persisted. I replaced the fuel pump with a Daewerks high flow pump that I bought from Colin but its still struggling to start especially when the car is warm or has been recently driven. Battery was tested and its good. I'm probably going to try replacing the fuel filter next. Maybe the used 550 injectors I put in aren't doing their job? Bad or improperly gaped plugs? Does anyone have any other ideas of what might be causing the issue? Any help would be appreciated.

 

Having similar issues. These forums are a ghost town.