Hi.
I've been thinking about my fuel line.
Is there any reason why I can't join the return to "B" or "C" or must it go to "A" ?

This is an injection system.

[Edited on 31/10/05 by piddy]
Rescued attachment Fuel line.JPG

the reason people normally say you should return it to the tank, is that the pump will suck fuel back down the return, which will reduce pressure at the engine. To what extent this happens, i dont know. Someone said the other day that they ran it back to b or c to no ill effect, however, i myself would do it back to the tank. It just feels right.

Might i suggest trying both and letting us know what difference, if any?!

Presumably though the return feed is being pumped back by the oversupply to the engine, If you returned it at "C" then it would have the potential to push the dirt back out from the filter into the tank.
or alternatively, if the pump is sucking then if there was no fuel in the return pipe at a given moment , would it then suck air into the sytem at B or C from the empty pipe?

Don't know much about fuel injection, but do know something about pumps. Pumps try to add pressure to whatever is fed into their inlet. If you feed it back into itself it won't like it much. At "C" the filter may act like a check valve ; "B" might work as any surplus pressue should go back into the tank.

Play safe and stick to "A".

isn't there also an issue with heat?

Sure i head something like, you put it in the tank to give it a chance to cool down. If you put it back into the pump, at idel you're pumping a lot more than you need so it just goes round and round, getting hotter and hotter........

probably rubbish but i remember it from somewhere

probably an example is how do motor manufacturers do it. Back to the tank I think. Thats a big clue.

atb

steve

Two big issues with this.

1 Air locks, if air gets in the system upsteam of the pump then the pump will not be able to draw fuel from the tank.. You can expect this to happen whenever you leave the car overnight if the injectors bleed down a bit.

2 Heat in the fuel, with injection a large amount of fuel is circulated off load, this will just get warmer as it slips around reducing power.

Best just to leave it simple, a flow and return to the tank.

Regards Mark

just had an idea.

How about having a circa 1000cc collector pot under the bonnet, maybe in the scuttle area, filled by a low pressure pump, with the high pressure pump drawing from this and returning to it too. Would eliminate all fuel surge, which i can promise is a very real problem - i knackered my pump last week when it temporarily ran dry.

I suppose that adds the weight and current draw of a second pump, but saves on a good length of pipe.

not a new idea, but any thoughts?

we will end up arguing what a swirl pot is next - deja vu.

atb

steve

quote:

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Originally posted by steve_gus
probably an example is how do motor manufacturers do it. Back to the tank I think. Thats a big clue.

atb

steve

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I am looking at doing exactly this, I bought a fuel pump from ebay and it has turned out to be an in tank unit , something i didnt consider when bidding. My plan is to fit it inside a 100mm dia collector pot and fit it in the engine bay on the drivers bulkhead and then feed it from the original mechanical pump on the crossflow, i will add a small bore return pipe to the tank and return the fuel reg outlet to the swirl pot.
My only concerns are the fact that it may allow the fuel to get warm and also the fact that i have a litre or so of petrol contained in the engine bay.The swirl pot will be made from some 1.5mm wall stainless tube with a welded cap one end and a welded flange the other with a bolt on top to allow access so should be fairly strong and crash proof.
Paul.

quote:

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Originally posted by JoelP
just had an idea.

How about having a circa 1000cc collector pot under the bonnet, maybe in the scuttle area, filled by a low pressure pump, with the high pressure pump drawing from this and returning to it too. Would eliminate all fuel surge, which i can promise is a very real problem - i knackered my pump last week when it temporarily ran dry.

I suppose that adds the weight and current draw of a second pump, but saves on a good length of pipe.

not a new idea, but any thoughts?

---

Looking under the bonnet of my 2004 laguna diesel the other day there seems to be a 'pot' on the drivers side against the bulkhead. Its got a low pressure feed of diesel to it, and a very delicate pipe running to the engine. (Looks like a slightly more rugged bendy bit from a Mcdonalds straw!) Looks like pot thingy would hold a bit over a half litre. Im guessing its the fuel filter. Renault are happy having a pot of fuel under the bonnet.

what suprised me was the fuel feed line from the tank. Looks rather a lot like a flimsyer version of nylon air tubing. I would have thought sva would kick that out on a kit car!

atb

steve

Hi would you need a return if you are running a carb setup?

I'm using a low pressure pump at the back feeding a swirl pot at the front with a high pressure pump then feeding the fuel rail. There is a return from swirl pot to tank, and fuel rail to swirl pot. Really didn't want to run dry on those long high speed bends