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Air Lock In Fuel System, Fuel Injected, High Pressure Pump


Guest shaggy

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Guest shaggy

All,

 

I've got a problem, well many at the moment, but this one seems to have me baffled.

 

For quite some time now, I've been taken home on a low loader following a short trip out. The most recent was today following having my zetec condemned after a rr session. I broke down no less than 5 times, on the hard shoulder on most occasions.

 

Problem seems to be maintaining a good pressure in the fuel rail, usually 3 bar to feed the very thirst TB's.

 

I have changed the high pressure pump, fuel regulator, and even the fuel filter. I have cleaned the fuel tank, but yet the problem persists.

 

Its only today that the penny has dropped, and most of the incidents occur when the tank is quite low, AND after a sharp left hand bend (outlet for the fuel is on passenger side).

 

Now I have the low pressure pump mounted under the tank, and the swirl pot (incl fuel pump) and filter and regulator mounted above the tank (no room under the tank). To resolve the lack of fuel pressure, I have resorted to releasing the fuel line after the filter, before it goes to the fuel rail, splashing myself with loads of fuel, then turning the pumps on to ensure a good flow of fuel goes into an empty container before reconnecting and going on my merry way. Now the process of getting the fuel running into the container can take a good 20 seconds as much air is expelled out of the pipe before fuel starts to pour out.

 

So MY diagnosis is that air is pumped into the system as the fuel swooshes to the non exit side of the tank, and thus causes some kind of blockage either between the low pressure pump and the high pressure pump, or the HP pump and the filter.

 

Then again I may be talking a load of tosh (which for those of you who know me, is not too far from the truth).

 

Filled up with fuel, taken her out for a good thrashing, and she behaved quite well. The car also gave me no trouble at all, hence my theory about the air lock.

 

Can anyone confirm or dispute this? If this is the case, is there a cure, apart from mounting the swirl pot, fuel pimp, filter and regulator underneath?

 

TIA

 

Si

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Guest shaggy

does the return fuel line from the fuel rail feed to the swirl pot, and then a final return to the tank from the swirl pot?

No, the fuel rail does not have a return, instead, the fuel to the rail is tee'd off, one feed to fuel rail, the other to pressure reg, and then onto the swirl pot.

 

Works fine with good supply of fuel, just cocks up when tank low and on left hand bend.

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Guest ant.b

 

No, the fuel rail does not have a return, instead, the fuel to the rail is tee'd off, one feed to fuel rail, the other to pressure reg, and then onto the swirl pot.

 

Works fine with good supply of fuel, just cocks up when tank low and on left hand bend.

I had this on mine for ages , I used to avoid turning left when less than half a tank ! I experimented with the position of the pump that fills the swirl and eventually moved it to the bootfloor along with the swirl pot and that cured it , since then I ve used an in tank pump to feed the swirl with no issues apart from when I ran it out of fuel and killed the pump , so back on the boot mounted puller pump now and still working ok , but I do have a return from the rail to the pot

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Guest peter2b2002

bigger swirl pot, on my sierra doner i could get it to cut out if i went arround a round about too fast with a nearly empty tank, on my 2b the guage goes from 1/2 to empty on tight bends but it ok as there is a big 2ltr swilrl pot

peter2b

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by fuel rail i mean rail/regulator (on mine they're one and the same). I'd prefer it if the fuel flow travelled through the rail before reaching the regulator, as you're at the risk of trapping air in the rail, which might be giving you the problem (and initial bleeding problems).

That said, air should not be getting into the system after the swirl pot. Do you not have a return from the pot to the tank? This is essential. If you do, is it the highest outlet from the swirl pot?

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Every time you corner with low fuel and expose the fuel pick-up in a non baffled tank your low pressure pump sucks in air which rises to the top of the the swirl-pot. You must have a return to the tank from the highest point of the swirl-pot which allows this air to be returned to the tank. The swirl-pot should always be full of fuel only. The diagram below shows how it works. Not rocket science and you don't have to reinvent the wheel. Just do it right. There are slight variations but the basics are the same. It's a system that must be self bleeding just like a cooling system.

 

A swirl pot needs four pipes.

The pressure regulator is always effectively in the return from the fuel rail (for injection.)

The relative positions of the pipes into the swirl-pot are not accidental.

The LP pump can be very simple and of quite low output. After it has filled the swirl-pot for the first time its function is to replace fuel used by the engine and maintain bleed flow in the swirl pot.

The HP pump needs to be specced to exceed the desired fuel rail pressure under all conditions

 

Nigel

post-21-0-39122300-1370516360_thumb.jpg

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If you want to play and have a system that has only one line to the fuel rail then here's a diagram. It does introduce possible problems and I personally wouldn't bother with it. If you want problem free injection feed the diagram in the post above is the one to follow.

 

Nigel

post-21-0-20800800-1370517125_thumb.jpg

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Guest shaggy

Nigel and Grim,

 

you have both hit the nail on the head. I have cocked up on the plumbing side as I have the return from swirl pot to tank on the lowest port, instead of the highest port.

 

In another life I'll come back as a blonde

 

thanks again. What a great forum this is - now let the mickey taking begin........................

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i will be there at 10 am after sorting out Mr(heavyhands) Perry with his sheard bolts issues.. all this after 12hr night shift.!!!! oh and Simon. how many times did i ask if it was right!!!!! you plank !!!

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