Fuel pump alternative

[100SRV]

Hi,
I use a Facet solid-state fuel pump on my truck, this feeds a swirl pot in the front (about 2 metres away and 0.5 metres higher. The pump is situated below the bottom of the fuel tank so is gravity fed, a pre-filter is used (see seperate recent thread!).

The swirl pot is used to keep all the EFi stuff at the front of the car.

The primary problem is that the pumps seem to have a short working life, anything from 5000 miles to a few years. My perception of "short life" is based on the knowledge that I've never replaced a fuel pump on other cars I've owned.

Is there a more reliable alternative to the Facet interrupter?

cheers
100SRV

[100SRV]

Hi,
feeds a swirl pot which feeds a Rover 3.9 V8 running 14CUX EFi

I'm using a facet solid state "fast road" spec.

cheers,
100SRV

[100SRV]

Steve_D said:

Am I missing something here?
There should be a low pressure lift pump supplying the swirl pot and a high pressure pump below the swirl feeding the EFI.

You only mention one pump...if this is the case then the swirl pot is pointless.

Steve

ETA Should have also asked what size pipes you are using. High pressure pumps do not like sucking so the supply pipe should be getting on for twice the size of the outlet. If not then cavitation can occur which can kill a pump...thinks?

Edited by Steve_D on Sunday 26th October 09:33

There is a high pressure EFi pump below the swirl pot fed by a 10mm hose. I didn't mention this because the HP pump hasn't caused any problems.

[100SRV]

Hi Steve,
Solid state to fast road spec. Good point about the restrictor, I used to have one in the return line when running the engine with twin SU carburetters, I'll reinstate it in the swirl pot to tank line.

Thought there had to be a simple solution / installation error.
I'll check the delivery rates for the lift (problem) pump and the EFi pump to be sure the lift pump can keep up.

Thank you for the advice, always appreciate a second, more experienced point of view.

100SRV

[100SRV]

Hi,
OK, getting a bit more complicated now. The recirculation of the fuel is a bit of a problem in hot weather so I can see the need to return the rail to the tank.

Present arrangement is:


StevieTurbo proposes a restrictor in the return line to make the lift pump work:



The lift pump is rated:
7.0-4.0 PSI @ 145 litres or 32 gallons per hour

The EFi pump is rated:
2.54 KGF / cm3 43.25 lbs / square inch or 3 bar @ 150 litres or 33 gallons per hour

The lift pump is just shy of the HP pump by 5 litres/hour, I'd be amazed if I ever spend more than 30 seconds at WOT so the deficit can be ignored.

What should I do?
Send the fuel rail return direct to tank and restrict the swirl pot return to tank...
The spare port on the swirl pot can then be blanked and I spend 0 hours worrying about the demise of a fuel pump.

The above can be achieved by teeing the rail return into the tank return line AFTER the swirl pot exit restrictor. This means high volume flow rate returns to the tank to mix and cool while the lift pump has to do some work.

Thank you for the education!
100SRV

[100SRV]

andy-xr said:

When I had twin 40s on my car I put a silver top and a regulator on, with a gauge on the regulator so I could measure the flow rate. I preferred that than going for the smaller electric pumps as they burned out.

On my EFi setup I've got an injection tank, so swirl pot built in. Other people with similar setups have welded the tank to fit one, some others dont bother and just dont go below 1/4 tank. But the main pump for the EFi is a Sytec inline pump after the swirl pot, it's mounted just ahead of the tank. There's a pre installed regulator at the fuel rail for mine so I know it's set to 2.5 bar

Here's the one I have: http://www.ebay.co.uk/itm/SYTEC-MOTORSPORT-IN-LINE...

Thank you Andy,
the design of the tank and nature of vehicle use (severe gradients pitch and roll) mean that I prefer to use a swirl pot topped up by a LP pump. The vehicle often spends tens of minutes operating at roll angles up to 40 degrees and similar in pitch.
100SRV

[100SRV]

fatjon said:

This setup is a sure way to kill the high pressure pump. It draws fuel from the swirl pot, feeds it round the injector rail and returns it to the swirl pot. The vast majority returns to the swirl pot getting hotter on each cycle. Eventually the fuel is so hot that it kills the HP pump either by overheating or by trying to pump vapour. You need a tank return from the top of the swirl pot so cool fuel is cycled through the swirl pot by the low pressure pump and no vapour accumulates.

Hi fatjon,
having discussed this with a colleague last night I'm going to reject this as a red-herring. Why?

The HP pump has a flow rate of 149 LPH
The LP pump has a flow rate of 145 LPH
Swirl pot capacity is 1 litre

Most of the vehicle's use is with less than 60% engine power being used so the rate of return from the swirl pot will be quite high (perhaps around 60% of that pumped to the fuel rail).

This gives 89.4 LPH into the swirl pot with a further 145 LPH contributed by the LP pump - 234.5 LPH of which 233.5 will have to go back to the tank via the return line.

The tank has a capacity of 62 litres - over the course of a few hour's driving / green laning all of this will have passed through the fuel rail at some point so the net temperature will increase. The tank is stainless and has a large surface area so I would expect this to dissipate heat quite well.

Any more suggestions on the fuel pump?

100SRV

[100SRV]

Max_Torque said:

You need to check your maths! Currently, your tank would fill up and overflow!!

(hint, some of the fuel the LP pump moves to the swirl pot is also the same as the fuel "going round in circles" via the HP pump)

Hi Max Torque,
I was checking my maths using a spreadsheet but got myself confused ;-) so gave up until this evening.
100SRV

[100SRV]

Bump...any proposals for a fuel pump?

[100SRV]

226bhp said:

Yes I read it. So how is the car still running after 'tens of minutes' if the swirl pot isn't being fed?

The core question regards the unreliability of the fuel lift pump which pumps fuel from the tank to the swirl pot. The average life seems to be around 20000 miles, perhaps a bit more. I think they should last at least five times longer. Id like advice which:
1 Proposes a more reliable pump or
2 Highlights an error in the circuit design

One pump has been proposed and a different pump has been suggested, I'd like more suggestions or examples of similar installations please.

[100SRV]

Steve_D said:

Perhaps the issue is that there are times when the lift pump is running dry which will kill it in short order.
Is there scope for a new tank design. A tank of an inverted pyramid design would ensure a constant feed to the pump up until the point you have the car on its side.

Steve

Hi,
that is the odd thing, other than when I have completely drained the tank the pump is never heard running dry. The tank has a vee-section where the pick up is located, I try to keep at least 15 litres in when green laning (because I've run out of petrol once before and prefer walking for pleasure not necessity!).

I can't understand the reason for the short life other than the suggestion by one reply that maybe the pump doesn't have enough of a restriction so runs near to full speed for it's entire life.

I've purchased a combined fuel pressure regulator / sediment bowl along with another spare pump. I'll fit the regulator, increase the restriction and see what the result is. I am sure that the engine will receive plenty of fuel even if the lift pump runs at half the flow rate; I rarely use WOT so the fuel from the rail return will make up the difference when I do and if not, will return the unused fuel to the tank.

Thank you for the interest!
100SRV