Your fuel injector relay may be cutting out after your initial attempt at starting.

Locate the FI relay - under dash near hood release - a rectagular box, black or mustard in color with a six pin connector.

Pin 30 is always hot(red) fuse #7 from Battery Junction box, pin 87(Y/R) is for the fuel pump.

according to my Volvo Problem Solvers guide- in the '78 model year - to run the fuel pump - jump 30 and 87.

Jumping these terminals will allow you to see if the fuel pump is running OK.

If the fuel pump is ok and you jump these terminals and try to start the car and it runs, you'll know that it's the relay which is at fault.

Also you can test the injectors while they are out by using the jump method to run the fuel pump and lifting the air flow sensor plate to increase the fuel flow to the injectors.

Pull off the air inlet tube (the one that runs from the air filter box to the air flow sensor. Reach into the air flow sensor and you will feel a plate on a hinged arm. push up on the plate to simulate more air flow/more fuel to the injectors. All injectors are always spraying, not pulsing like the LH system.

Re: jumping terminals to start fuel pump

Before you go and jump the terminals on the FInjector Relay check to see that you indeed have a a '78 wiring set up. Look at the fuse box. There should be a label inside the cover. Fuse # 7 is always the Main Fuel Pump.

From '79 on fuse #5 is labeled "PrePump" and fuse # 13 is labeled Injector Relay/Instrument. If this is the case then you can simply Jump #5 and #7 to by pass the relay.

If #5 is labeled FInjector Relay - as it should be if you are wired as a '78 then you've got to do as I described above and jump the terminals on the Relay itself.

Good Luck