Activating a pump via an oil pressure switch.

[mudski]

So I'm up to the wiring part of the lift pump install. I want to run the pump via an oil pressure switch, around 10lbs, so it only comes on when the motor is actually running. Not just via the ignition power. I dont want override switches etc etc if it can be done without.
Therses a spare port on the LHS of the block I could use to access oil pressure, a big PITA to get to, but it might be doable. I first thought the switch would be just a two wire jobbie, so power runs through the switch from one terminal to the other. Not so. The two wire switches are actual for a gauge, so its a sender in fact. The switches are only a single wire.
So my question is.
How can I implement a single wire oil pressure switch in to turn on the pump?
Or is there a wire in the ignition side of the cars loom thats only powered when the engine is running? Not just with the ignition on.

[jff45]

In my conversion, I used the single wire TB45 oil pressure switch.

For my lift pump, I use a feature of the TB45E ECU that runs my pump for 5 seconds then stops. When I get oil pressure, the pump runs continuously.
This means that if the engine stalls, the lift pump stops.

Here's how I wired it. The fuel pump relay is the original relay for the EFI pump that's no longer there.
...

[mudski]

In my conversion, I used the single wire TB45 oil pressure switch.

For my lift pump, I use a feature of the TB45E ECU that runs my pump for 5 seconds then stops. When I get oil pressure, the pump runs continuously.
This means that if the engine stalls, the lift pump stops.

Here's how I wired it. The fuel pump relay is the original relay for the EFI pump that's no longer there.
...

Righto! O.k I might have to look at your diagram a few times. I have no relay but thought I will need one. So you added in the oil pressure switch? Plus the single wire on the switch is just an earth isn't it? And I would need a normally open switch I assume? As the OEM switch is opposite to what i need, I think.

How is your car running anyway? I've been meaning to swing you an email and ask.

[jff45]

Mine runs beautifully with the auto. Doesn't have the power level of yours but it's a much nicer car to drive now than with the TB45 engine.
It just pulls away effortlessly. Auto shift changes under boost is really nice.

If you remove the TB45 ECU from the diagram, all you need is 2 relays side by side.
Both relays powered from the same ignition source. Earth for the pump relay transits through the NC contacts of the 2nd relay so the pump relay will have no earth while there's no oil pressure because the oil pressure switch is holding relay 2 open.
Once there's oil pressure, relay 2 releases and the earth for the fuel pump relay is established via 87a.

[mudski]

Mine runs beautifully with the auto. Doesn't have the power level of yours but it's a much nicer car to drive now than with the TB45 engine.
It just pulls away effortlessly. Auto shift changes under boost is really nice.

If you remove the TB45 ECU from the diagram, all you need is 2 relays side by side.
Both relays powered from the same ignition source. Earth for the pump relay transits through the NC contacts of the 2nd relay so the pump relay will have no earth while there's no oil pressure because the oil pressure switch is holding relay 2 open.
Once there's oil pressure, relay 2 releases and the earth for the fuel pump relay is established via 87a.

Err ok. Ill need to sit down and figure this out with two relays.
Im wondering if i have a wire in the loom somewhere thats only powered when the engine is running. Then i could use this to switch the relay on.

Sent from my SM-P600 using Tapatalk

[jff45]

Err ok. Ill need to sit down and figure this out with two relays.
Im wondering if i have a wire in the loom somewhere thats only powered when the engine is running. Then i could use this to switch the relay on.

Sent from my SM-P600 using Tapatalk

No need for such a wire. The pump can't run until the oil pressure cuts the earth of the 2nd relay.

Let's discuss it via email..

[Rumcajs]

Im wondering if i have a wire in the loom somewhere thats only powered when the engine is running. Then i could use this to switch the relay on.

There is. You could use alternator return signal to charge lamp (it goes 12V+ when alternator is charging) this feature is commonly used to run "alternator charge relay" in heavy vehicles. You could also include oil switch in to that circuit and that way you would have best of both worlds. ..... Indeed that's how subtank fuel transfer pump module is controlled/operated.

Also it would benefit everyone if you keep the line of communication on this public aka in this thread, I'm sure there are many who'd like to know how this can be done.

Cheers

[jff45]

Yes, point taken.

Mine is wired as shown in the diagram I posted.
I think Mark did the same but without the 5 second connection through the ECU that's only an option with the TB45.

I'm sure he'll post when it's up and running.

[Rumcajs]

I have borrowed the idea with oil pressure switch as well as without. Here is my effort, I can't see any obvious issues. I had a second look at how subtank module is wired and it seems that strangely Nissan just uses the alternator charge lamp signal as earth/ground control/signal to subtank module which is weird.

Fuel_pump_circuit_with_oil_pressure_switch.jpeg Fuel_pump_circuit_without_oil_pressure_switch.jpeg

[jff45]

I like the way you draw it to match the factory diagrams.

Personally, I don't think both alternator charge and oil pressure need to be combined.
My reasoning for preferring the oil pressure model is that there's historically more risk of losing the alternator charge than losing oil pressure.
Of course, with a bypass on the lift pump you don't really risk being stranded but it's nice to have everything running as it's meant to.

Good info about the sub tank pump. I didn't know that.