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Re: [T3] FI fuel pump ordeal


On 11 Nov 2005 at 22:51, Tony Rongey wrote:

> >If I had to guess, I'd say that you've got your intermediate pump
> >plate assembled wrong. It can go together 8 different ways, but only
> >one of them works right. 

> I'd be inclined to agree based on my first experience
> disassembling a pump.  Took me 8 tries to get it to
> work :<

Okay, I see that you've worked your way up the learning curve the 
hard way. Don't you hate it when you take something apart and THEN 
discover that there was some secret to how it went together that you 
didn't think to look for as it came apart.  ;-)

> In this case though, the pump quit pumping while it
> was on the car.  Since that first experience I've been
> real careful about knowing how the plate goes back on.

I still suspect that there's some other explanation. I don't think 
that piston works its way back and forth too much, and the piston and 
bore should be pretty nicely lubricated with gas flowing all around 
it. It's hard for me to imagine that bore wearing much. I wonder if 
your rubber plug could be coming apart in a way that lets gas thru 
the piston, but I'd expect you to have found that easily, so I'm just 
shooting in the dark here.

> I actually got one to work for a while by clipping off
> one or two coils of the spring to reduce it's force. 
> That's what makes me think the inner part of the
> piston bore is worn.  Nothing happens when the pumps
> are unmolested.  Once I add the block which preloads
> the piston both the pressure and relief work fine,
> which means the piston is traveling back from the
> preloaded position.  It just won't move from the fully
> closed position.

I believe the end of that rubber plug is pretty much hemispherical 
when it is new. Its diameter is about 4mm. If yours is deformed, it 
may be sticking in the outlet and this would allow the piston to 
intrude farther into that cavity, which might be part of the problem.

The bore is expected to leak a bit, and the piston has OD grooves 
that are designed so that it leaks more before the piston is pushed 
back. If the rubber plug has collapsed, maybe the piston is sticking 
in too far, and just leaking too much.

The leak allows the pump to expell air to prime itself. The air will 
slowly leak past the piston until there is enough gas in the pump to 
build up enough pressure to open the exit check valve.

> I was really hoping there would be a sleeve there since that would 
> provide hope of fixing that problem.  

The piston is 7mm diameter. I suspect that if your bore was actually 
oversize now, you could bore it out and sleeve it. I just doubt that 
this is actually the problem.

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

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