[T3] Fuel pressure leak

[Jim Adney]

On 25 Aug 2013 at 9:36, Jacob Adam Schroeder wrote:

> When my car is running, I have a constant 28 psi on my fuel line.  The
> second I turn off the key, the pressure immediately drops to about 20 psi.
> 
> The same is true before starting.  In other words, when I turn the key to
> the first click, the PSI goes up to 28.  As soon as the pump clicks off,
> the pressure drops immediately down to 20psi.  The pressure stays around 20
> psi for an hour before it slowly begins to drop.  Last night, it was around
> 17psi when I went to bed (about an hour after I turned the engine off), and
> in the morning I was around 5 psi.

This is perfectly normal, nothing to be concerned about.

> Should I be concerned about this?  It is always 28 psi when running, but
> I'm concerned that whatever is causing the leak could be giving me a super
> rich mixture.  If so, what is the likely culprit and is it an easy fix?  I
> understand that our fuel pumps are difficult to find.

I rebuild the pumps, so don't worry about finding a new one. One of 
the major causes of pump death is water and dirt that gets in via a 
cracked "overflow" hose. The OE part is NLA, so I finally made up a 
kit to replace it, and my parts should outlast the OE parts. The 
price is $25-33, including shipping and instructions, depending on 
the year.  

> I began to investigate my fuel pressure after I experienced some sort of
> "vapor lock" issue on Friday.  After the 25 mile commute from work to home,
> my wife had me go back out for groceries.  When I tried to start the car, I
> got nothing and I could hear air bubbles in the gas tank (presumably coming
> in through the return).  Any thoughts?

This is a fairly common hot weather problem. During the heat soak 
after shutdown, the engine compartment gets hot enough to boil the 
gas inside the lines. The gas vapor gets pushed backwards into the 
gas tank where it recondenses, because it's cooler there, then air 
gets sucked back into the fuel loop as the engine cools. It's not 
clear where the air gets in, but backwards thru the injectors is one 
possibility.

The solution is to install a switch to run the pump briefly, before 
you try the starter. Just run the starter until the bubbles stop, 
then start the car. I have a kit for that, too, which includes the 
switch, wiring, mounting bracket, and instructions for $10 (MT) or 
$11 (AT.)  

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Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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