I would make sure that the fuel pump relay is not at the heart of the problem.

Make a short jumper wire, and when the problem shows it's ugly head, unplug the relay and jumper between the yellow/red and red wire on the relay connector.

The Red wire is directly from the fuse panel and should have battery voltage when the ignition switch is on.
The yellow wire goes directy to the fuel pump.
This will prove or disprove correct operation of the relay.

I've never owned a 80 Model, but I did have a 81 Model with K-Jet, Bosch Ignition and a Frequency valve.
On it, the fuel pump relay was located under the dash close (maybe attached to) to the steering wheel column.
I remember having a problem such as your's, and I remember driving with the fuel pump readily accessible so I could trouble shoot the problem.

hope this helps
steve