98 Jeep Cherokee won't start at times. I checked the fuel pressure and it is below spec at about 26 psi. It should be 35-45. This has the in-the-tank fuel pump with no external fuel filter. When you pump the accelerator, it will start. I'm told that pumping the accelerator should not make a difference given that the fuel pump is electronic. How do I know if it is a bad fuel pressure regulator and not a bad fuel pump?