Considering I'm doing a DIY EFI installation and I've read the various books on EFi out there I feel a bit ashamed to be asking this question but here goes anyway!!!

Does a fuel injection pump run all the time? If so, does that mean I want one that accurately matches the maximum required fuel flow? I thought the fuel regulator just takes the required pressure and hoses any unused stuff back to the swirl pot... But does that mean that the pump runs 100% of the time???

I've worked out I need a pump capable of (at full chat) running 15Gallons/hr @ 3bar... Does that mean if I get one which will do 30gallons it will always be pi$$ing at least 15Gallons/hr back into the swirl pot?

I'm worried that even with a swirl pot I could get fuel heating up if there's that degree of over-pumpage!!!! I also worry the bigger pump is going to take up unecessary Amps (therefore BHP) by running....

I can't help but feel that the pumps must cut out when the pressure is sufficient but then why is a pressure regulator required??

thanks!!!

my pump runs all the time, i dont have a swirl pot either.

mind you my car isnt on the road so take no notice of me

Yes, the pump runs all the time. A pressure sensitive valves diverts excess fuel back to the tank or swirl pot.
I added fuel injection to my old TR7 with a V8. I found that on a hot day The fuel would get quite warm. I believe that this was mainly due to the fuel rail (around which fuel was circulated) picking up radiated heat from the (fairly hot) inlet manifold.
This fuel temperature rise concerned me. If I had kept the car, I would have tried to reduce under bonnet temperatures and perhaps add some sort of a fuel cooler (I believe the XJS uses a fuel cooler)

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Originally posted by JonBowden
Yes, the pump runs all the time. A pressure sensitive valves diverts excess fuel back to the tank or swirl pot.
I added fuel injection to my old TR7 with a V8. I found that on a hot day The fuel would get quite warm. I believe that this was mainly due to the fuel rail (around which fuel was circulated) picking up radiated heat from the (fairly hot) inlet manifold.
This fuel temperature rise concerned me. If I had kept the car, I would have tried to reduce under bonnet temperatures and perhaps add some sort of a fuel cooler (I believe the XJS uses a fuel cooler)

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The fuel went straight back to the tank - so obviously it took a while to warm the fuel.
The fuel didn't get very warm - if I remember right, it would be about right to wash your hands with if it were water.
I did notice that the engine idled less smoothly at the same time - I assumed that this was due to the warm fuel.

If the temperature rise was due to heat pickup rather than excess pumping, then putting some thermal insulation round the fuel pipes in the engine bay might have helped.

I haven't seen anyone else complaining about this problem, so I guess that it's not that big a deal - I'd just go ahead and build my system - then fix a problem if it occurs.

I think you would want a continuous circulation of fuel as if the fuel flow was only that was needed to run the engine, in traffic the fuel would heat up in the pipe and boil. The same applies to carbs with the fuel return to the tank which helps prevent vapour lock.

The pump does run all the time. It will take fuel from the tank (gravity fed) via a filter, through the pump out to another filter, 8mm fuel pipe to fuel rail, out the other end of the fuel rail to the presure regulater (keeps presure in the rail at 3-3.5 bar) and excess fuel gets returned straight to the tank. I have done 6000 miles and never had a problem with a MK baffled tank, no swirl pot required.

The benefit of swirlpot is purely to replace the float chamber in carbs. Obviously as fuel injection is direct feed (no float chamber) under heavy cornering it is easy to run out of fuel temporarily as the fuel surges away from teh tank outlet.. The swirl pot stops this and also allows de-airation of the fuel.

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Originally posted by TangoMan The swirl pot stops this

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