[NocturnalCreations]

What year is your wifes malibu and what motor does it have?

When it fails to start does it crank but not start?

When you first shut off the car was the pressure still at 55psi?
If it was then you lost pressure during your oil change you probably have a leaking injector, bad return line or fuel pump.

I dont think the pressure regulator can make you loose pressure unless its leaking, wich you would see...or possibly leaking into the return line, im not sure about that one

Do you smell gas? If so look between the upper and lower intake around the injectors for puddles of fuel.