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Author: Subject: EFI Fuel Return

posted on 25/8/14 at 07:10 PM Reply With Quote
EFI Fuel Return

Can anyone tell me 'how much' fuel is returned to the tank in an EFI system?

I've fitted an Impreza pump to my Jag's fuel pump hatch, and am looking to sit it in a plastic container to act as a swirl pot, with the return filling the pot, seems the Subaru owners often do a similar mod.

Just trying to work out how many / how big holes I need to put in the pot to keep it full.

Imprezza pump on  E Type hatch
Imprezza pump on E Type hatch

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posted on 25/8/14 at 08:01 PM Reply With Quote
Isn't the amount returned simply the flow from the pump at the pressures you are running minus the amount used by the engine.

So the maximum returned will be the maximum pump flow rate.

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posted on 26/8/14 at 08:45 AM Reply With Quote
Remembering that it's the maximum flow rate at the pressure the system is operating at.
Assumptions in the above relate to the pump running up to a regulator pressure, with the return from that.

I've been here recently, asking the question on the return rate of a typical bike pump. No-one could offer an answer, but I do have data for the MK4 Fiesta Pump:

Open pipe: 2.4 litres/min

Return volume under pressure:

At 42 psi - 900ml/min
At 38 psi - 1100ml/min

The engine (when running) will then consume the return as it requires it.

[Edited on 26/8/14 by motorcycle_mayhem]

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posted on 26/8/14 at 09:02 AM Reply With Quote
Bearing in mind when it matters will be at WOT/full chat, I'd assume nothing is returning... So the holes into the sump/pot have to be able to allow an equal (greater) amount into the pot from the main section of tank, as the pump takes out.

"A witty saying proves nothing" Voltaire

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