Intermittent issue of RB30 Patrol Fuel Pump Control Unit

[dom14]

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.

[Yendor]

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.

So you have connected a wire to supply direct power to the fuel pump (green wire with a red trace) at the fuel pump control unit and it doesn't play up?. If so, this would eliminate any possible bad connection at the fuel pump or in the earth side of the fuel pump.

[dom14]

So you have connected a wire to supply direct power to the fuel pump (green wire with a red trace) at the fuel pump control unit and it doesn't play up?. If so, this would eliminate any possible bad connection at the fuel pump or in the earth side of the fuel pump.

Yeah, but kinda still not sure. I had couple of times the pump not pumping the other day. Not 100% sure whether that was due to tank being low in petrol or real connection issue near the tank. I filled up the tank with enough petrol yesterday and atm trying being patient to see if the petrol "unpumping" happens again.
I will update the outcome soon.

[mudnut]

Doesn't hurt to run extra earths anyway, as the body and chassis have rubber mounts between them.

[dom14]

So you have connected a wire to supply direct power to the fuel pump (green wire with a red trace) at the fuel pump control unit and it doesn't play up?. If so, this would eliminate any possible bad connection at the fuel pump or in the earth side of the fuel pump.

Yeah, it appears the connection(s) between the Fuel Pump Control Unit and the fuel pump is fine.
I drove it with the direct connection from the Fuel Pump Control Unit for couple of days now without any dramas.

So, the problem is between FPCU & the battery power line to it(I think).
Either FPCU is faulty or the connection to it from the battery/ignition.

I guess the next step is to check the power to the FPCU and make sure all the incoming power lines
to FPCU are properly powered when ignition's ON.

[Yendor]

Yeah, it appears the connection(s) between the Fuel Pump Control Unit and the fuel pump is fine.
I drove it with the direct connection from the Fuel Pump Control Unit for couple of days now without any dramas.

So, the problem is between FPCU & the battery power line to it(I think).
Either FPCU is faulty or the connection to it from the battery/ignition.

I guess the next step is to check the power to the FPCU and make sure all the incoming power lines
to FPCU are properly powered when ignition's ON.

Or you could trade it in for a nice GU

[dom14]

Or you could trade it in for a nice GU

Can't afford it. Besides, I like these GQ trolls.
Something blokish about the shape of the GQs.
I feel like a pollie with a long member.

I have a new PEEL brand tachometric relay.
I'm wondering whether I can wire it up to do the job the FPCU is doing(or rather not doing due to being faulty).
For the petrol priming, I might be able to use a self resetting delay relay circuit(runs for five seconds then disconnects, then need a power reset to do that all over again).
For the ongoing power to the fuel pump can be controlled by the tachometric relay, so as long as the
engine's running, the fuel pump will run. As soon as the engine stops( as in an accident), the fuel pump will stop as well.

I'm reluctant to replace FPCU with a used one, 'cos they will be as old as my (possibly) faulty one, so can become defective in no time.

[Yendor]

Can't afford it. Besides, I like these GQ trolls.
Something blokish about the shape of the GQs.
I feel like a pollie with a long member.

I have a new PEEL brand tachometric relay.
I'm wondering whether I can wire it up to do the job the FPCU is doing(or rather not doing due to being faulty).
For the petrol priming, I might be able to use a self resetting delay relay circuit(runs for five seconds then disconnects, then need a power reset to do that all over again).
For the ongoing power to the fuel pump can be controlled by the tachometric relay, so as long as the
engine's running, the fuel pump will run. As soon as the engine stops( as in an accident), the fuel pump will stop as well.

I'm reluctant to replace FPCU with a used one, 'cos they will be as old as my (possibly) faulty one, so can become defective in no time.

I was expecting a bigger bite then that

Tachometric relays were used in the early years to control electric fuel pumps by most manufactures. The FPCU in your GQ is similar to tachometric relay.

Do you have a wiring schematic for the Peel relay?

[dom14]

I was expecting a bigger bite then that

Tachometric relays were used in the early years to control electric fuel pumps by most manufactures. The FPCU in your GQ is similar to tachometric relay.

Do you have a wiring schematic for the Peel relay?

I don't, but from what I remember it's fairly straight forward.
One wire goes to the ignition coil(green I think), two red wires,
one is the trigger the other is the "active" line, and the black wire(earth).
All together four pins from memory.

I'm sensing you're telling me there are better ways to do it?!

[mudnut]

Mate, grab a secondhand one from a wreckers and try it. I got one for 5$ as a spare.