rodgling
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 posted on 12/8/14 at 08:56 AM |
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why do my fuel pumps keep dying?
I'm running a twin fuel pump setup, one at each end of the tank, to avoid fuel starvation in corners. It solves this problem really well, but
the pumps keep breaking.
Both pumps are standard spec for my engine (M3 evo 5 bar pumps), with the outputs T'd together, and the return from the rail T'd again so
that both pumps can be cooled by the return flow.
Since the FPR maintains 5 bar of pressure on the fuel rail, both pumps will be pushing against 5 bar so I don't think having an extra pump
present should upset them? I guess they will be flowing half as much fuel as they normally would... could that overheat or damage them?
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jeffw
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| posted on 12/8/14 at 09:03 AM |
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If I read that right....everytime you go round a corner one pump will be pumping fuel and one will be trying to pump air? This might explain the
issue...also I'm not sure how you are cooling the pumps using the return lines? A diagram would help.
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tegwin
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| posted on 12/8/14 at 09:06 AM |
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If I am seeing this correctly with the two pump outputs T'd together you will get all kinds of weird dissymetry of pressure between the two
pumps as the fuel sloshes around in the tank between the two pump inlets causing surges in the pumps.... I would want to see a non return valve
after each pump before the pipes 'T' together.
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Dick
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| posted on 12/8/14 at 09:09 AM |
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Most fuel pump are cooled by the fuel and they rely on the fuel as the lube for the moving parts in them as well. They like a bit of air over them for
a bit extra cooling. If you are running 1 on each side then I would say in corners the pump is running dry and this they don't like.
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loggyboy
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| posted on 12/8/14 at 09:22 AM |
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If starvation is your concern, you would be better off with 1 feeding a swirl pot and the second feeding the rail from the swirl pot.
Mistral Motorsport
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britishtrident
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| posted on 12/8/14 at 09:26 AM |
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The pumps are running dry, a single central out let from the tank to low pressure pump feeding a swirl pot.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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wylliezx9r
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| posted on 12/8/14 at 09:27 AM |
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quote:
Originally posted by loggyboy
If starvation is your concern, you would be better off with 1 feeding a swirl pot and the second feeding the rail from the swirl pot.
^^^^^^What he said !
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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rodgling
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| posted on 12/8/14 at 09:36 AM |
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Fair enough, looks like I need a swirl pot. Although doesn't the low-pressure pump end up running dry occasionally in that setup - presumably
the low pressure pump is able to deal with this?
The current setup was really a cheap way of avoiding fitting a swirl pot since I originally had two fittings in the tank for a pump and a sender at
opposite ends, so it was easy to replace the sender with a second pump.
I guess the simplest solution would be to get someone to convert the tank with an in-tank swirl pot? Or is an external one a better bet? Who would be
a good bet for this in the Cambridge area?
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blakep82
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| posted on 12/8/14 at 09:39 AM |
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My tank has a 3" diameter, about 1.5" deep "swirl pot" type thing, which is fed by a 1" diameter hole in the tank, fuel
goes in by gravity, and won't slosh back out under cornering, you'd only need 1 pump if you do that. The tank would have to be really
empty before it ran dry
But I agree, running dry, but when one is running dry, you'd surely be losing fuel pressure too?
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[Edited on 12/8/14 by blakep82]
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rodgling
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| posted on 12/8/14 at 10:00 AM |
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Thanks all for suggestions. Blake: no, with two pumps running it's absolutely fine under cornering when one is (presumably) dry. Your setup
sounds like a potentially low-cost solution, something like my CAD below?
so if the return feeds the in-tank swirl pot you can avoid the need for a second pump? I guess you need to be careful with sizing the mini-swirl pot,
too high and it won't fill up once the fuel level drops, too low and it won't be effective.
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FuryRebuild
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| posted on 12/8/14 at 02:03 PM |
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Twin pumps are generally run in parallel in a fail-over mode, now simultaneously. As stated above, your arrangement will sort starvation to the
injectors, but will starve your pumps.
take a look at this solution from Tweeks: http://www.demon-tweeks.co.uk/motorsport/fuel-tank-baffles/demon-tweeks-easy-pour-fuel-tank-baffle. You can
then run one pump.
Does your pump live in a sump, as it were?
M
When all you have is a hammer, everything around you is a nail.
www.furyrebuild.co.uk
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rodgling
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| posted on 12/8/14 at 02:17 PM |
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Thought about using foam / baffle type stuff, but it would interfere with the swing-arm level sensor. Of course I could change that for a float in a
tube, but then I'd have to modify the tank anyway...
No sump, my tank is just a big open box, hence the problems with surge. My current plan is this:
i.e., add an open-topped cylinder around pump 1, which will supply the fuel rail and should never run dry. Pump 2 will just keep the cylinder topped
up. Pump 2 will run dry sometimes, but since it's acting like the low-pressure pump in a proper swirl pot arrangement, and not fighting any
pressure, presumably it should be OK with this?
This should be the cheapest solution as it's just the addition of a simple tube of aluminium to the tank - but looks reliable & effective?
Comments?
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jeffw
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| posted on 12/8/14 at 02:44 PM |
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Don't use a HP pump instead of a LP pump....
Your best bet is to use a swirl pot to feed the HP pump and use a LP/lift pump to fill the swirl pot. Put the return from the fuel pressure reg into
the swirl pot and then a return to the tank.
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wylliezx9r
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| posted on 12/8/14 at 02:56 PM |
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This is what you need to do : I managed to create this setup for under £100 with the pumps.
 
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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wylliezx9r
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| posted on 12/8/14 at 02:59 PM |
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quote:
Originally posted by rodgling
Thought about using foam / baffle type stuff, but it would interfere with the swing-arm level sensor. Of course I could change that for a float in a
tube, but then I'd have to modify the tank anyway...
No sump, my tank is just a big open box, hence the problems with surge. My current plan is this:
i.e., add an open-topped cylinder around pump 1, which will supply the fuel rail and should never run dry. Pump 2 will just keep the cylinder topped
up. Pump 2 will run dry sometimes, but since it's acting like the low-pressure pump in a proper swirl pot arrangement, and not fighting any
pressure, presumably it should be OK with this?
This should be the cheapest solution as it's just the addition of a simple tube of aluminium to the tank - but looks reliable & effective?
Comments?
Using this setup P2 could still run dry and thus self destruct. And P2 should be a low pressure pump as it is just being used as a pull up pump.
I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best
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rodgling
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| posted on 12/8/14 at 03:14 PM |
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quote:
Originally posted by wylliezx9r
quote:
Originally posted by rodgling
Thought about using foam / baffle type stuff, but it would interfere with the swing-arm level sensor. Of course I could change that for a float in a
tube, but then I'd have to modify the tank anyway...
No sump, my tank is just a big open box, hence the problems with surge. My current plan is this:
i.e., add an open-topped cylinder around pump 1, which will supply the fuel rail and should never run dry. Pump 2 will just keep the cylinder topped
up. Pump 2 will run dry sometimes, but since it's acting like the low-pressure pump in a proper swirl pot arrangement, and not fighting any
pressure, presumably it should be OK with this?
This should be the cheapest solution as it's just the addition of a simple tube of aluminium to the tank - but looks reliable & effective?
Comments?
Using this setup P2 could still run dry and thus self destruct. And P2 should be a low pressure pump as it is just being used as a pull up pump.
True - are low pressure pumps fundamentally different in that they're happy to run dry then?
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Paul Turner
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| posted on 12/8/14 at 03:16 PM |
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quote:
Originally posted by wylliezx9r
This is what you need to do : I managed to create this setup for under £100 with the pumps.
Exactly like this on mine (with a filter between the swirl pot and the pump - the LP pump also has a built in filter). No issues in 10 years.
One word or warning. Make sure you use the correct fuel pipe. Even the best rubber correct spec stuff form acknowledged suppliers simply cracks after
3 years or so. Mine is now all TFE braided hose and fittings form Think Automotive. Not cheap but should be good for many years.
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sdh2903
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| posted on 12/8/14 at 03:48 PM |
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Hi Dave
When I swapped to the bike engine peter sorted me a baffled tank with a sump on the bottom to feed my low pressure pump for the bike carbs. Never any
sloshing or fuel surge. This plus a swirl pot and a hp pump and you would be sorted. The tank was also the exact profile of the std GKD tank so was a
straight swap.
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garyo
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| posted on 13/8/14 at 08:13 AM |
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You can also use a gravity fed swirl pot. Essentially it's a cheat way of putting a sump in your fuel tank without having to pay for a welder.
Strap the swirl pot sideways under your tank and plumb in the outlet. Strap your high pressure pump alongside and bob's your uncle.
Gary
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rodgling
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| posted on 13/8/14 at 03:25 PM |
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So in my last diagram, if I replace P2 with a low pressure in-tank pump then does that look like a sensible setup? E.g.
http://www.fuelpumpsonline.co.uk/low-pressure-feeder-pump-itp377-hi-p3029-2106-p.asp.
Thanks sdh2903, that's also an option, probably more expensive though - need to decide whether to replace the tank or modify what I've
got. Might be slightly different to your situation as you were running on carbs rather than driving a high pressure fuel rail - to go with
Peter's solution I'd want to hear from someone who's tried it with a high pressure pump...
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