[T3] Vacuum Leak

[Jim Adney]

On 8 Jan 2011 at 18:02, Adriel Rowley wrote:

> > From: jadney at vwtype3.org

> > I've not seen good results from rebuilt injectors. My impression is 
> > that they don't always meter out the correct amount of fuel. New or 
> > used bosch 007s are what you want. Keep in mind that if the plug is 
> > fouling, the problem may not be too much gas, it may be too little 
> > compression or too much oil leaking past the rings.
> > 
> Well, will see if that is the case.  Bob's test should show this, and if 
> the injector is not spraying what appears to be the same, might have a 
> spare injector.  There are no knew ones, as far as I know.  Oh, and the 
> rebuild is for the seals and maybe the valve; the windings are still the 
> same.

I don't think you can tell much from the appearance of the spray. If 
it looks bad, then it IS bad, but if it looks good, then it may still 
be bad. A good looking spray cone can still contain 50% too much or 
too little gas. 

> Well, will see if that is the case.  Bob's test should show this, and if
> the injector is not spraying what appears to be the same, might have a
> spare injector.  There are no knew ones, as far as I know.  Oh, and the
> rebuild is for the seals and maybe the valve; the windings are still the
> same.

If some of your injectors have been rebuilt, then I would be 
suspicious of them. I've fixed cars that ran poorly just by replacing 
"rebuilt" injectors with correct Bosch injectors. I have a suspicion 
that in the rebuild process the rebuilders are not always careful 
about which nozzles they install in which injectors. Bosch made 
different injectors for a reason.

> > I also install the seal on the nose of the injector first. Then you 
> > have to make sure that it seats nicely in the manifold when you 
> > install it.  

> How?  Not real easy, especially with the fuel line fighting one the 
> whole way.  The F.I. hose seems to be stiffer than the other low 
> pressure fuel hose (F.I. hose not my doing nor approved, especially 
> considering it is 7mm).

Use 5/16" fuel line and don't try to connect all the hoses before you 
insert the injectors (assuming you have it all apart at that point.) 
If you've just pulled them out to check the spray pattern, then the 
hose should not be fighting you if you're just putting it back where 
it came from.

> > > Where is the vacuum leak?
> > 
> > ??? You're the one who reported finding it. You tell us.
> > 
> What I mean is, you say it is not the injector seal, so what else could 
> it be?  The spray was general, so only know what general area, and I am
> under the impression stock F.I. gaskets do not leak.  That seems to 
> elemenate the possibilities...

I don't think there is a vacuum leak. Any gasket CAN leak if it's not 
installed properly. Surfaces have to be clean and nuts have to be 
tight, etc. 

The most common place for leaks is at the joints between the IAD and 
the intake runners. Those can usually be cured by loosening all THREE 
parts and letting them find their own best position. This can be 
difficult if the connecting hoses have already been bent and 
distorted. I sometimes have to straighten intake runners that have 
been bent out of parallel and rotate hoses which have an offset to 
them due to being installed poorly before I got to them.

OTOH, leaks at those joints are rather unimportant, because they 
basically leak right into the IAD, where the pressure is measured, so 
a leak there is very little different from opening the throttle 
slightly more. It might make a noticable difference at idle, but 
nowhere else.

But start by checking the compression on the cylinder that is 
fouling.

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