Sometimes won''t start... on 1993 Volvo 940

'93 940 wagon(B230, non turbo) won't always start. Once it starts, it runs fine, no power issues. Either after sitting, or when hot, it won't always start. Replaced the fuel filter, wondering it it's the fuel tank check valve, pressure regulator or maybe the fuel pump isn't supplying enough pressure at starting. Where is the fuel tank check valve located? Can I change it without removing the tank?

Asked by for the 1993 Volvo 940
There are a few possibilities, and I would start with a fuel pump relay and an injector relay. The fuel pump relay is the white relay behind the ashtray, the fuel injector relay is attached to one of the shock towers in the engine compartment.
You may have an RPM sensor too, but check the codes in the ECM and Ignition computers and post the codes and I can give more advice.
Look here too:
Thanks for the help. It was in fact the fuel pump relay.
Hey did you hear a humming sound before you reaplace that fule pump relay . my 940 is doing the same thing but I hear a humming sound in the middle of the car