I have an issue and not sure what the cause. On 4.6 I have been having some intermittent hard starts after doing ccv , intake and valve cover gasket. I suspected a fuel issue and hooked up the gauge to the rail. Pressure hold steady at around 50 psi, when running fine. At one point it had a hard start and noticed that the gauge was showing zero pressure . Any idea why I would get 0 pressure intermittently ?