I just replaced both my fuel pumps and if they have a check valve, they're built into the pump and screw in the front. I have replaced everything on earth except for EHA, Fuel Distributor and Cold Start Valve which I never need here in So Cal. Put new seals and injectors in today as well as a new fuel filter and had just put in a new fuel Acumulator. OVP is new. I could shove the old one back in there and see if it makes a diff. Not sure what to try next. Once she starts...no problems and idles perfect.