22 replies to this topic

[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. 

 

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

 

 

 

A gear pump is a positive displacement pump, it will make some " pressure " when at cranking speeds, but not enough to lubricate the engine enough for running. my volvo b230 engine will not like idling at less than 1200 rpm as it dosnt make enough oil "pressure" below this to lubricate the cam. dry sumped engine is an external pump same thing. the super cars probably wont fire until it sees oil pressure. 

[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.

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.

I did think of that, but the engine would still run for a while with the fuel in the fuel bowl, so it wouldn’t stop the fuel pump straight away.

If the original poster was keen on an oil pressure switched system I would think a kill switch would be a better option. If you lose oil pressure and it cuts the ignition (spark) and the fuel pump, this would stop the engine straight away.

For example if you’re racing and lost oil pressure it’d stop you if it killed spark. If it just killed the fuel pump you’d still be full throttle for a minute or so with no oil pressure

I still think this is a bit elaborate for a road going mini

[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

 

 

 

 

? 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???

 

 

yes;  87a is normally closed so at rest 30 is connected to 87a which means the fuel pump is connected to the power input terminal

 

with the 86 - 85 input circuit energised (ignition on and the oil pressure switch closed i.e. no oil pressure), the relay changes from 30 - 87a connected to 30 - 87 connected which illuminates the oil pressure warning light

 

once the engine is started and oil pressure builds the input circuit de-energises when the pressure switch opens and the relay reverts back to it's normal/'at rest' state of 30 - 87a connected

 

if oil pressure is subsequently lost whilst the ignition is still on, then the input circuit will re-energise and the relay will switch power from the fuel pump (87a) to the oil pressure warning light (87)

 

the problem is that when you then turn off the ignition, the input circuit de-energises and the relay reverts back to it's normal state of connecting the main power input (30) to the fuel pump (87a)

Edited by KTS, 10 February 2025 - 11:06 PM.

[68+86auto]

The easier and more effective solution is to install an inertia switch just like Rover did. They are available on eBay etc. You'll just need to add a relay as they aren't designed to handle the pump current. In the event of a collision it will cut out.

 

 Screenshot 2025-02-11 090800.jpg   12.49K   0 downloads

 

The other solution I've seen is a special relay that's sold over here intended for LPG conversions but people use them on petrol too. It connects to the coil negative and shuts off the pump if the engine dies.

 Screenshot 2025-02-11 090935.jpg   15.82K   0 downloads

Edited by 68+86auto, 10 February 2025 - 11:18 PM.

[Ethel]

It is worthwhile if you have high pressure pump running all the time, like with a turbo engine & you can envisage losing a fuel line connection without smacking something hard enough to trip an inertia switch.

 

If you connect the earth wire from the oil light to output to the pump on the relay (use terminal 30), the it'll earth via the pump when it's not running & when the relay is closed there'll be 12v on both sides of the bulb & no current flowing through it - same as how the ignition light works.

 

You'll have 87 & 87a free so you can feed the pump from the "ballast bypass" terminal on the solenoid when cranking the engine. The oil pressure switch can control the solenoid's coil to engage the running supply when it isn't cranking - depending on whether the pressure switch opens or closes when there's oil pressure will dictate which terminal.

[gav]

Does this help?

 

Circuit Description

When the ignition key is set to position II, normal ‘Ignition On’, Battery positive is supplied, via the white wire, to the ignition Coil, ECU, and to one side of fuse 1–2 in the fuse box (the top fuse). The engine has, therefore, all requirements for starting. In addition, with power at fuse 1–2, the coil of the Fuel Pump Relay has battery volts at its coil terminal 86. The other side of the coil, at terminal 85, is however not connected to chassis until the oil pressure switch closes, which only occurs when the engine starts and sufficient oil pressure has been generated. The Oil Pressure Lamp has battery positive at one side, via the white wire. Its other side is connected to near chassis via the Fuel Pump and its associated Ballast Resistor. The lamp will therefore illuminate, indicating low oil pressure. (Note: Since the current taken by the bulb is very small, the combined voltage drop across the Ballast Resistor and stationery Fuel Pump windings will be extremely small.)
When the Ignition Switch is set to position III, the ‘Start’ position, battery positive is now also applied to the coil of the Starter Relay at terminal 86, via the white/red wire. Since the other side of the coil at 85 is connected to chassis, the relay energises. Battery positive is therefore switched to the Solenoid, via contacts 30 and 87 which then supplies the Starter Motor. Whilst the Starter is energised, a separate auxiliary contact on the Solenoid, feeds power to the Fuel Pump. The pump now runs, filling the carburettor bowl with fuel.

Whilst the Ignition Switch is at position III, connection is still made to the contact at position II, the normal ‘Ignition On’ position, thus maintaining the initial ‘Ignition ON’ conditions previously described. The Oil Pressure Lamp will, however, extinguish whilst the Solenoid is energised, as battery positive is applied to both sides of the lamp in this condition.
After the engine starts, the ignition key is released and returns under spring tension to position II. The ignition supply remains connected, but the supply to the Solenoid and therefore the Fuel Pump is removed. The engine continues to run however, using the fuel in the carburettor bowl, which will last for approximately 30 seconds. Meanwhile, as soon as oil pressure reaches approximately 5psi, the Oil Pressure Switch closes, thus energising the Fuel Pump Relay. Its contacts, between 87 and 30 therefore close, switching a permanent battery supply, via the In Line fuse and the Fuel Pump Ballast Resistor, to the Fuel Pump, which runs at a reduced voltage to prevent overheating. The voltage at terminal 30 of the Fuel Pump Relay is also routed, via the white/orange wire, to the Oil Pressure Lamp. This lamp is now supplied with battery positive at both sides, causing it to extinguish.

In the event of the engine stopping for any reason, whilst the Ignition Switch is still at position II, e.g. in a crash, then the Oil Pressure Switch will open, causing the Fuel Pump Relay to de-energise, which will therefore remove the battery supply from the Fuel Pump and return the near chassis connection to the Oil Pressure lamp, the latter then illuminating.

 

Attached Files

•  turbooilpressure2015.png   143.69K   2 downloads

[Ethel]

Expect the colour in to the 15A is wrong. Not that it matters here.

 

You could use the ordinary, normally open, pressure switch but you'd need an ignition dependent supply to the pump - you could use a mosfet to get a normally open control for the relay, from a normally closed switch.

 

Getting something combined with a relay could be simpler For Example

[Pietervdp]

It was meant for safety indeed, in the event of a crash where the fuel pump would keep pumping fuel. But I didn’t realise it’s such an uncommon thing to do, and that the cooper S just had it wired on the ignition. It should be possible with a relay, even maybe use a feed from the starter to prime, but perhaps a inertia switch is already safety enough. That switches off the fuel pump (through a relay) in case of a sudden movement (a crash)