22 replies to this topic

[Pietervdp]

I’m installing an electrical fuel pump with an inertia switch. But I would also like to add an oil pressure switch to stop the pump when the engines dies. I have a t-piece to use both the normal oil pressure switch for the dashboard warning light and an oil pressure gauche. The oil pressure switch for the fuel pump needs to be a different kind then the one for the dashboard light (1 with 3 connectors to switch with the starter).
Does anyone know if a 3-way “T-piece” to connect all 3 is a bad idea (if I can even find one…)?
Or would there be an easy way to switch the dashboard light with the 3 connector type pressure switch?
Anyone any idea?

[Avtovaz]

wont that make it hard to start as you would need oil pressure for it to prime the pump and then fire?

[68+86auto]

You can use relays to do what you want.

 

There are also small boxes which will cut out the fuel pump based on if the engine stalls by detecting the engine RPM.

Edited by 68+86auto, 09 February 2025 - 11:41 PM.

[Lplus]

wont that make it hard to start as you would need oil pressure for it to prime the pump and then fire?

It most certainly will - though I believe there are exotic/supercars which have this feature as standard.  Presumably they have oil pumps which start pumping immediately as opposed to mini pumps which can take a while to pull oil up and make pressure.

[gav]

I have the ERA Turbo oil pressure switch wiring diagram if it helps?

[timmy850]

You could have fuel pump priming when the key is cranking, then once it’s started the power could go via your oil pressure switch

Personally my electric pump (factory fitted on a mk1) just gets power when the key is on. I’m trying to think of a situation that you’d need an oil pressure switched pump and there isn’t much I can think of? If the engine is off but the pump is on it’ll prime the fuel bowl but will stop pumping once it’s full.

[Lplus]

You could have fuel pump priming when the key is cranking, then once it’s started the power could go via your oil pressure switch

Personally my electric pump (factory fitted on a mk1) just gets power when the key is on. I’m trying to think of a situation that you’d need an oil pressure switched pump and there isn’t much I can think of? If the engine is off but the pump is on it’ll prime the fuel bowl but will stop pumping once it’s full.

Perhaps in the event of a crash which damages a fuel line/carb in the engine bay but which leaves power to the pump?  Unlikely but eliminated by the use of the mechanical pump.

[Avtovaz]

 

wont that make it hard to start as you would need oil pressure for it to prime the pump and then fire?

It most certainly will - though I believe there are exotic/supercars which have this feature as standard.  Presumably they have oil pumps which start pumping immediately as opposed to mini pumps which can take a while to pull oil up and make pressure.

 

 

 

 

that i know of, no car has an electric oil pump, they are always gear pumps weather they are wet or dry sumped. 

[Avtovaz]

hold on, so this car must have a ecu, either factory or aftermarket. It will have a wire from the ecu to control the fuel pump which should prime the system and then wait until it sees a signal returning from the crank sensor.

 

 

My Microsquirt, Megasquirt, and my speeduino ecus all do this and you can set the time etc. 

[Spider]

On one hand this set up I can see might be a good idea for safety, however, I've never run them that way, over many cars and many years, I've only ever wired them as per the original Cooper S so the pump is live on the key.

[KTS]

a relatively simple way of doing this is to use the existing oil pressure warning lamp circuit to control a relay that supplies power to the fuel pump

 

The (White/Brown?) wire from the warning lamp to the pressure switch is at 12V when the pressure switch is open, and 0V when it's closed, so you can use a connection from this part of the circuit to drive the relay

 

one downside of this setup is that the relay will draw a small current to keep the coil energised, which in turn will cause the lamp to glow a little, so choose a relay that draws the least current

[Avtovaz]

sorry just re read a lot of this and its a carb isnt it on an electric fuel pump conversion. sorry

 

probably start ok with the fuel in the float if its not evaporated or anything.

 

 

use a 5 pin relay, 

 

 

85 ignition live that was going to the oil light bulb

86 going to the oil switch

 

30 feed to fuel pump

87a to fuel pump

87 to oil pressure warning bulb

 

and earth the other side of the bulb.

 

 

i hope i got that right lol

Edited by Avtovaz, 10 February 2025 - 07:37 PM.

[Lplus]

 

 

wont that make it hard to start as you would need oil pressure for it to prime the pump and then fire?

It most certainly will - though I believe there are exotic/supercars which have this feature as standard.  Presumably they have oil pumps which start pumping immediately as opposed to mini pumps which can take a while to pull oil up and make pressure.

 

 

 

 

that i know of, no car has an electric oil pump, they are always gear pumps weather they are wet or dry sumped. 

 

You misunderstand, by pumping immediately, I mean the engine driven gear pump produces pressure almost immediately the engine is cranked.

[KTS]

sorry just re read a lot of this and its a carb isnt it on an electric fuel pump conversion. sorry

 

probably start ok with the fuel in the float if its not evaporated or anything.

 

 

use a 5 pin relay, 

 

 

85 ignition live that was going to the oil light bulb

86 going to the oil switch

 

30 feed to fuel pump

87a to fuel pump

87 to oil pressure warning bulb

 

and earth the other side of the bulb.

 

 

i hope i got that right lol

 

not really; what's required is that the fuel pump only has power when the ignition is on and the oil pressure switch is open.  what that circuit does is cut power to the fuel pump only when the ignition is on and the oil pressure switch is closed

 

a standard (4 pin) make and break micro relay is enough

 

30 +12v supply

87 to inertia switch (..and then on to fuel pump)

86 connects to White/Brown wire

85 to earth

[Avtovaz]

 

sorry just re read a lot of this and its a carb isnt it on an electric fuel pump conversion. sorry

 

probably start ok with the fuel in the float if its not evaporated or anything.

 

 

use a 5 pin relay, 

 

 

85 ignition live that was going to the oil light bulb

86 going to the oil switch

 

30 feed to fuel pump

87a to fuel pump

87 to oil pressure warning bulb

 

and earth the other side of the bulb.

 

 

i hope i got that right lol

 

not really; what's required is that the fuel pump only has power when the ignition is on and the oil pressure switch is open.  what that circuit does is cut power to the fuel pump only when the ignition is on and the oil pressure switch is closed

 

a standard (4 pin) make and break micro relay is enough

 

30 +12v supply

87 to inertia switch (..and then on to fuel pump)

86 connects to White/Brown wire

85 to earth

 

 

 

 

? its a 5 pin relay, 87a is normally closed, so when the oil light is on, itll open energise the switched side and put the oil light on, when the earth goes from the pressure switch the pump goes on as the windings are open, and then 87a is now activated???