[T3] Fuel pump and Wiring

[Jim Adney]

I've been out of town, with a broken laptop, and with the flu. Other 
than that we had a great Thanksgiving. I spent most of my long 
weekend in bed, waited an extra day, and then drove home on monday 
instead of sunday. I'm still under the weather, but I'm home now, 
getting better and getting more real sleep

Hope this explains why I've been unresponsive lately.

So here goes:

On 25 Nov 2011 at 14:13, Adriel Rowley wrote:

> In the summer before leaving for University the Squareback was bowing
> the fuel injection curcuit's fuses. Checked the wires and all seemed
> fine. Put in new fuses and got the two clicks but the pump did not
> sound good. None of the fuses are blowing now. The pump sounds like a
> clogged/stuck garbage disposal and does not sound like it is pumping
> fuel, i.e. no bubbles in the tank. Could the pump cause a fuse to blow
> with too much draw? What is going on? 

Noisy pumps usually mean a restriction in fuel feed to the pump. At 
some point I suspect this might blow a fuse, but I've never seen it 
get that bad. The first thing to check would be to pull off the hose 
to the pump inlet and just see if you get a good flow of gas out of 
that hose. It should be a pencil diameter stream that comes out 
disturbingly fast.  

Do this outside, no smoking, no flames or sparks in the area.

If you get just a dribble, you need to work your way back toward the 
tank. The most common problem is a clogged filter; second most common 
is a clogged filter screen in the tank. 

If the tank is close to empty and the passages in the bottom of the 
tank have been clogged with rust, then you may just be drawing air, 
so make sure the tank is at least half full when you do this.

> Also where can I find a fuel pump wiring diagram? Want to be sure all
> is right. 

Ch. 4, pg 18, item 9 (at the bottom of the diagram)

The one thing you could check would be to put a voltmeter across the 
pump relay to verify that there is less than 0.1 V of voltage drop 
across the relay contacts when the pump is running. Very 
occasionally, I've seen those relay contacts become poor and fail to 
deliver full voltage to the pump. So far, I've only seen this in '72.

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