Not a bad project by the way, figuring out what you have to remove and what you do not have to remove is half the battle. I did the passenger side in half the time of the driver side. Happy to give “pointers” if anyone is interested.
Lots of things can cause that.. I would make sure I had good pressure on both fuel rails as a first easy test that doesnt require taking anything apart.. just spin the little cover off the end of the fuel rail (it literally looks like the cap thats on the stem of your tire air pressure port) and press the nipple in with a golf tee, It should squirt a little fuel out with some pressure. Might try a can or two of fuel injector cleaner!