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LP Pump Troubles

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Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#281739
I was reading the EJ20 not running right post, and read that the LP pump was the problem. I have a tip for LP pump users, as usually a tip that came about by doing it the wrong way myself first. So, do you have LP pump problems?

Well, what sort of low pressure pump are you using?

If your using a facet pump (or most pumps) then you will need a strainer prior to the fuel pump. In a stock beetle tank there is a small strainer attached to the fuel pick-up inside the tank.

When people do conversions they usually remove that stock strainer because they weld bigger fuel outlets into the tank. They figure they don't need the strainer because they will run better filters elsewhere.

But the pump doesn't like that. Especially the facet pump. The facet pump is a solid state coil with a magnet that moves back and forth in a steel cylinder, pushing fuel past a check valve with each stroke. Dirt will pass through the pump with no real problems, but small rust flakes from the fuel tank won't. The flakes will stick to the magnet which moves back and forth, and will actually get stuck between the magnet and the cylinder bore. This makes the pump start working temporarily, on and off as it pushes some flakes away only to get jammed again later. You can fix the pump by pulling it apart and cleaning the rust flakes and particles out the way.

The prevention however is to put a strainer prior to the fuel pump as the factory did.

You don't want a filter filter, like a cardboard filter, as a filter will catch the real fine particles and by doing so causing too much pressure loss for it to be installed prior to a pump.

You want a strainer type filter, a coarser mesh type device. I find the inline glass ones with replaceable, and cleanable meshes to work quite well. The glass lets you see how dirty it is, and if the fuel is flowing.

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Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

11CAB If ya got it....Baja it

4,674 posts · joined Aug 2002 ·

#281746
The standard FI filter used on the Kombi's and later T3's will do the same job. 133 133 511 is the part No. I think.
It has a larger fitting on the outlet for the pump side.
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Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#281872
Just out of interest, is the kombi one glass so you can see through it?

The one above is easily rebuildable and cleanable. Plus they aren't very expensive and available at most automotive stores like Autobarn etc.
Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

pete wood 23 Windows of Awesome

6,828 posts · joined Jan 2004 ·

#281876
I am using a standard fuel filter ($5 plastic opaque thingo) in line between the tank outlet and my facet fuel pump. I thought placing a filter there was the obvious thing to do. I have never had an issue with this pump.

Also, another thought. If you are going to the trouble and expense of fitting a great new efi motor (or system) the least you can do is recondition your fuel tank at the same time. POR15 sells a kit to strip, clean and seal the inside of the tank for about $45. It also seals up any pinholes or porrous welds at the same time. This is important for modfied tanks, eg. mine. Seems like cheap insurance to me.
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PurpleT3 Fahrvergnugen

880 posts · joined Apr 2003 ·

#281917
$45 for the POR fuel tank kit!! Where did you buy it from., I paid $99 + S&H.
Ain't nothin' like the wind in your hair.

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#281946
pete wood wrote:I am using a standard fuel filter ($5 plastic opaque thingo)
I'd change it for a glass strainer type one, or change it regularly.

As I said, those type fuel filters are a cardboard type element and are more restrictive than the strainer ones. Especially when they get dirty. It's ok to put them on the discharge of the pump because the pump simply forces it through.

But on the suction side of the pump it has to suck it through there. Fuel has a very low vapour pressure meaning it doesn't take much for it to get vapour lock and other strange running problems if you try to suck it through a restrictive filter.

That's why I didn't put a standard filter in front of my LP pump to start with. I initally skipped on the strainer too as I thought the facet would pass small particle without any real problems, which it would if the main moving part wasn't a magnet 🙂
Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

PurpleT3 Fahrvergnugen

880 posts · joined Apr 2003 ·

#281999
Would the vapour lock problem happen with a stock mechanical style fuel pumps as well? If so does this mean fuel filters should be after the fuel pump and only strainers before?
Ain't nothin' like the wind in your hair.

Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#282051
PurpleT3 wrote:Would the vapour lock problem happen with a stock mechanical style fuel pumps as well? If so does this mean fuel filters should be after the fuel pump and only strainers before?
Yes.

The standard beetle has the screen in the tank attached to the outlet fitting. Some of the mechanical fuel pumps also have a screen inside of them. It's normally behind a 13mm or so nut which is on the rear face of the pump, just about touching the belt. Clean it once in a while.

So the standard beetle has 1 or 2 screens. If you want to then add a filter, then stick it between the pump and the carby.

It's even more important if you have an EFI car with only a high pressure pump (just about every stock EFI car). They instead have a large area strainer bag attached to the pump inside the tank. It's designed to basically never be blocked or cause any pressure loss.

By the way, fuel has a different vapour pressure in summer and winter. The petrol companies do this on purpose. They kinda set it up to always be on the verge of vapour lock at a certain temperature. It's a balance between having fuel which is difficult to vapourise, and won't run as it won't burn properly, to a fuel which vapourises too easily causing vapour lock.
So you get the worst vapour lock problems during a freak hot day in the middle of winter.
Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.

seagull Compulsive Aussie Vee Dubber

4,979 posts · joined Dec 2003 ·

#282233
Brad had some neat fuel filters for sale 😉
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Andy Andy\'s Adventures

2,820 posts · joined Nov 2002 ·

#282320
Another thing to remember about the paper filters is they block when they get water through them. The paper swells when wet blocking the fuel flow. They are best mounted vertically, in the bottom out the top, this way they catch the water and don’t get the paper get wet.
Even though I don’t run mine on the inlet side anymore (stock mechanical pump, carb motor), when changed regularly I’ve not had problems with them on the inlet side.

MikeM Buggy Head

1,429 posts · joined Aug 2003 ·

#282328
I like the idea of using a fuel strainer before the pump. But I'm not a fan of using glass filters or strainers. One rock flicked up of the road can hit the filter, crack the glass, and all of a sudden there's fuel everywhere. Not good. This would be even more likely on an offroad car.

In my opinion every thing in the fuel delivery system should be rubber, metal or impact resistant plastic.

Is there a commonly available plastic strainer? Maybe the stock VW FI filter that 11Cab mentioned would be the go?


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Baja Wes V6 Baja Pioneer

3,119 posts · joined Aug 2002 ·

#282444
The glass one I have is about 4mm thick, it's pretty strong looking. It came with a hard bit of plastic that clips over half of it (mainly to stop the unit unscrewing itself), and you can still see the other half. It gives adequate protection.

If you were real worried you could simply zip-tie a piece of rubber over the filter.
Wes - www.offroadvw.net - 200HP Quad Cam V6 in a VW Baja - with climate control... 🙂
www.taylorcycles.com.au - My DH MTB racing brothers shop.