This is an intermittent issue which I think is related to a weaker connection somewhere between the Fuel Pump Control Unit & Fuel Pump itself.
The earth is a separate black wire goes to the fuel pump, from the back end of the Fuel Pump Control Unit(by the looks of it).
I'm thinking of creating a dedicated earth from rear chassis to important units like fuel pump.
Do you guys think that's a good idea or an overkill?
It's not possible to check the quality of the connections to the fuel pump without lowering the tank(Long Range tank, pump connectors can't be accessed from the access point inside the back of the car), hence the reason for my slackness with correctly diagnosing the problem.
But, I think the Fuel Pump Control Unit is not at fault. I think it's a weak connection in the wire somewhere, either the earth or the +12V wire. ATM, I have wire directly connected to the fuel pump +12V that goes out of the Fuel Pump Control Unit to keep the pump going reliably.
One of the benefits of the Fuel Pump Control Unit is to prime the carby with a bit of petrol to get it started when we first turn on the ignition(really handy when dual fuel with carby) and more importantly to cut power to the fuel pump when the engine suddenly stops while the ignition is on(as it happens in an accident) This is done by piggybacking the connection to pump(or rather receiving an deactivation/activation signal) via Oil Pressure Switch on the engine block. Electronic switching circuitry inside the Fuel Pump Control Unit does that. So, when the oil pressure drops(as in engine's stopping while the ignition is on), the Fuel Pump Control Unit cuts the power to fuel pump(Dark Green wire with a red stripe that comes out of the Fuel Pump Control Unit).
See the circuit diagram I posted.
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