Low Pressure Fuel Pump

[Guest danny_samb]

I'm ordering a fuel pressure gauge later so I can check the pressure from the low pressure pump into the swirl pot, and from the high pressure pump into the fuel rail. Then I'm going to move the low pressure pump near the outlet of the tank so the doesn't have to lift the fuel then push to the pot. There is approx 12" of hose it's being dragged through before the pump. The car will idle fine so it must just be providing enough for a steady tick over. Put the engine under load and it coughs splutters then dies. Turn the ignition on and off a few times so the low pressure pump puts some fuel in the pot then it will run for a few minx I'm guessing until the pit is empty again.

[Guest 2b cruising]

Certainly sounds like a low pressure volume fault.

Have you checked all of you LP pipe work is clear. Even the inner tank pipes. If these are split or cracked you will get this problem and leaks obviously won't show because they are in tank.

 

 

[Guest danny_samb]

Iv got no pipes in the tank all pipe work is external. I think it's the location of the low pressure pump. Going to try moving it and see what happens

[stevedohc2b]

It could be something blocking the pipe from the tank, a blob of sealer sucked up the pipe, easy check remove and blow through.

If flow from low presure pump is slow. Also check the return from fuel rail.

Stephen

[Guest danny_samb]

Just took the pipe off the swirl pot that comes from the low pressure pump, I had to turn the ignition on 9 times to get the pump to pump fuel out the hose.

So I'm thinking it's struggling to much to drag the fuel up and pump to the pot. Left it 2 mins and then took another 4 times for the fuel to pump out the hose as if all the fuel had gone our the hose back into the tank

[Guest 2b cruising]

You have a pipe in the tank from your fuel sensor unit to the bottom of the tank. These get blocked easily. There is also a gauze filter on lots of them.

This pipe is also susceptible to splitting at the top of tank. Therefore the lower the fuel level, the worse the pump efficiency.

It is also best to fit the low pressure pump at least level with the bottom of the tank and if possible a bit lower.

Fluids find there own level so you will not suffer from suction head losses.

Also the nearer the tank and he LP pump is the better.

You deffo have either a blockage, pipe or pump fault.

How come your fuel pump is on a timed switch feed. You have return to tank from swirl pot so no need for it to turn off. I wander if it is something semi floating blocking the pump feed. Then letting go when there is no negative pressure at the end of your feed pipe.

Edited April 26, 2015 by 2b cruising

[Guest danny_samb]

I have no pipes in my tank. The outlet on my tank is right at the very bottom if the tank. If I was to remove the hose I would loose all the fuel out of my tank. Don't all fuel pumps run for a few seconds when only turn the key 2 clicks. They don't run continues until the engine is running.

[sj-bradley]

Yes, that should be the case that the fuel pump stops if the engine is not running. It's a safety issue.

 

You don't want the pump to continue pumping fuel in case of an accident which stops the engine and breaks the fuel pipe somewhere.

 

Hence the 2-3 seconds of initial pumping then stopping.

 

Simon.

[Longboarder]

Facet give minimum dry lift for their cubes as 12 - 84 inches. I doubt you are exceeding the pumps specs. Either there is a pipe blockage, blocked 'spawn of the devil' filter or a duff pump.

 

Nigel

[Guest danny_samb]

I thought the cube has a maximum dry lift of 30cm.

Once the fuel is at the pump it lifts it easy it's just getting the fuel to the pump. It takes about 9 primes to get the fuel to the pump then if not in use after a few mins it drains back out as there is no check valve in the cube.

[stevedohc2b]

I would still remove pipe from pump and blow air back in to tank and take sender out and have a look to check all is free, if the feed is from bottom any crud will settle at bottom and get sucked down pipe. I had a bit of a gasket get sucked up mine that is fed from top. i have a silver top pump. if then all ok replace cube cheap enof. i do carry a spare low pressure and high pressure pump as had both fail over time.

 

Stephen

Edited April 27, 2015 by stevedohc2b

[Guest 2b cruising]

I thought the cube has a maximum dry lift of 30cm.

Once the fuel is at the pump it lifts it easy it's just getting the fuel to the pump. It takes about 9 primes to get the fuel to the pump then if not in use after a few mins it drains back out as there is no check valve in the cube.

If it drains back every time after a few minutes, would it need priming 8 or 9 times every time you stop.

Surely this would be illuminated if the pump was sited below fluid storage level.

It is all sealed units and pipe work so what be wrong plumbing it like this.

No priming would be needed, just slight pumping to get up to pressure.

[sj-bradley]

Surely this would be illuminated if the pump was sited below fluid storage level.

 

Is this a "light bulb" moment? And please don't call me Shirley ...

[Guest 2b cruising]

Hahahahaha pml.

At least it would throw some light on it.

Edited April 27, 2015 by 2b cruising

[Guest danny_samb]

That was my plan to move the low pressure pump down to the same level as the tank outlet. Then it will grab it feed the pump. Does the high pressure pump need to be mounted flat too. As at the minute the outlet of the pump is higher than the inlet.

Do I need a breather on my tank.

Also I have a non return valved installed o the line from the fuel rail back to the swirl pot could this be causing me problems