[urq] Fuel Pump surge - still having problems

[Ben Swann]

Claus,

I sure hate to have to get rid of this tank.  I don't think I'll be able to approach 20
gal capacity and fit into this space like this tank does.

I have to admit the feed is horrible.  I took the car around this afternoon and when I
got home the problem was so bad the car was starving for fuel at even very low power.
Seems once a little air/vapor gets in the feed line it gets worse and worse.

It does seem weird there are bubbles forming when the tank is even over half full.  I am
pretty sure the problem begins to occur even if not driving, so I don't think it is due
to slouching around.  The pickup on this tank is down low in a separate well, so always
the intake is covered with fuel, unless empty past the lowest guage reading.

I think this problem is caused by the restrictive feed line - the pump "suction" is
causing the fuel to vaporize (cavitate) it is not necessarily air, but fuel that has
vaporized.  Your description below is somewhat descriptive.  The slope of the line makes
a difference.  If I lift the part of the line going into the pump, it will even cause
the car to stall - pump just sucks vapor and not fuel.

I looked at my lines again - I may have a few too many fittings and some line size
changes - these don't help.  I can rework, but still would be good to divert the fuel -
maybe can be cooled somewhat by an in-line accumulator - similar to a small surge tank.

So the only way you could get rid of the bubbles is using a fuel cell?

Ben

-----Original Message-----
From: Claus Vegener [mailto:vegener at post7.tele.dk] 
Sent: Thursday, April 17, 2008 4:09 PM
To: Ben Swann; a.sigal at bluewin.ch
Cc: urq at audifans.com
Subject: Re: [urq] Fuel Pump surge - still having problems

Recirculation the fuel in this way will heat up the fuel.

That's why it is supposed to go to the tank, or an fuel cooler had to be at 
the return line.
I had also problems with air bubbles in the supply line to the pump; but the 
issue is a bit different.
But I agree, the bubbles is from fuel slouching in corners in the original 
Urq tank.
I installed a fuel cell instead of the tank (in fact 2 small ones to have 
differnt fuel)
just flat in the trunk and have still less gravity to help
as the fuel pump is inside the trunk at the right side.
1) return line must go to bottom of tank to prevent air bubbles
2) I have first one 200 l/h Bosch pump, but that is not enough for 500 Hp 
even it should be.
    So 2 in parallel - the second started from a boost/rpm matrix in the 
034EFI
3) 2 inline fuel filters with glass for visibility - and I noticed, that if 
they catch bubbles,
they could stand just before the pump intake or the top of the filters 
(sloping downwards to the pumps a bit) for 30 km making troubles.
Systems from a house radiator central system for freeing air don't work ;
 but raising the pumps a bit, so bubbles could run upwards as air want, make 
the pumps to "eat" the bubbles at once.
And solve the problem. So not so much concern about gravity. The pumps 
should be able to suck a little - but not with air.
Claus
----- Original Message ----- 
From: "Ben Swann" <benswann at verizon.net>
To: <a.sigal at bluewin.ch>
Cc: <urq at audifans.com>
Sent: Thursday, April 17, 2008 8:27 PM
Subject: Re: [urq] Fuel Pump surge - still having problems


> I'm beginning to like this idea as a solution - it would also tend to keep 
> the filter
> sock blown free of any restriction and apply additional positive pressure 
> to the intake.
>
> I'm not quite pictureing exactly what you are describing, but kind of like 
> the idea of a
> hard 1/2" Cu line going directly into the tank - coupled by a small 
> Fernco(rubber pipe
> joiner).  The return line could feed into the tee.  Another tee into the 
> hard line could
> use the return line to tank fitting to flow in the opposite direction - 
> providing
> additional fuel feed instead of acting as a return.
>
> Doing this would be a lot better than performing any surgery on the 
> otherwise perfectly
> good tank.  Maybe need to feed a tiny surge tank to prevent any voids - is 
> that what you
> are suggesting.
>
> I think there is a solution in the works - some Cu pipe, fittings, tees, 
> Mapp torch - it
> has to at least result in improved flow into the pump.
>
> Now if I can just drive the car enough to clear out remaining 14 gal of 
> fuel -
> problematic with sloppy shifter that has also been driving me nuts - at 
> least I found
> the problem was a loose ball on the shift link.
>
> Appreciate any input into this scheme.
>
> Ben
>
>
> -----Original Message-----
> From: Ado Sigal [mailto:a.sigal at bluewin.ch]
> Sent: Thursday, April 17, 2008 1:50 PM
> To: Ben Swann
> Cc: urq at audifans.com
> Subject: Re: [urq] Fuel Pump surge - still having problems
>
> I believe that your problem is that under acceleration, the pump manages
> to draw the air from the fuel surface. Below 1/2 tank suggests this to
> be the case. A proper surge baffle of decent capacity, which Ur and most
> tanks with outside pumps are missing, would be a solution. (reason why
> in tank pumps don't have this problem, is because there is always decent
> surge baffle pool, and large pump intake close to the bottom). If you
> don't want to open the tank, other solution would be to return the fuel
> directly in front of the pump intake, instead of elsewhere in the tank.
> Simple longitudinal small capacity self bleeding cylinder (top line from
> the tank, bottom to the pump, and fuel return on the side) directly
> before the pump, should solve the cavitation and fuel starvation
> problem. In this scenario, the amount of fuel drawn from the tank would
> be only the amount of fuel used by the engine.
>
> Regards,
>
> Ado
>
>
>
> Ben Swann wrote:
>
>>Essentially what you say that I'm "flowing way too much fuel to return it 
>>to the pump
>>unused" is how it is done usually.  If not I'd like to know.
>>
>>Still - I'd like to find out how to keep the cavitation from happening.  -
>>some point during running, the fuel starts to bubble and cavitation during 
>>running.
>>
>
> I do notice it seems to happen more as the tank goes to below 1/2 -
> still a lot of fuel in the tank tho.
>
>>Ben
>>
>>
>>
>
>
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