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RE: [T3] fuel pump woes


On 3 May 2002, at 21:54, nathan howell wrote:

> When you switch the car on the pump
> comes on and then off as it should, so the relay is fine.

The relays develop resistance in the contacts, so they can sound fine and 
appear to work, yet they don't pass current well. This is still a possibility.

> The problem as it is described to me, is this...
> 
> The fuel pump turns on with the engine, in order to produce 31 psi it
> has to have resistance in the circulation line. This is done with a kind
> of check valve in the pump. My check valve is not functioning, therefore
> no resistance, and no good pressure. The fuel is just racing around at
> full bore. It is having a hard time getting up to 31 psi. That is what
> he explained to me. Does this sound wrong in some way?

There is an overpressure valve in the pump, which also acts as a check valve 
when you turn the pump off. It is the overpressure function that you're worried 
about here, because that allows excess pressure to bleed back to the tank.

If you think the pump output is leaking past the overpressure valve, you can 
test this by clamping the overflow hose (rearmost off the pump) while the 
pump is running. If this makes the pressure come right up (should be almost 
instantly) then this IS your problem.

I HAVE seen this problem in pumps left unused and dry for several years.

-
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************

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