[T3] Question re F.I. fuel pump cutoff

Jim Adney jadney at vwtype3.org
Fri Apr 15 11:15:35 PDT 2011


On 15 Apr 2011 at 12:43, Robert Bills  wrote:

>  The fuel injection fuel pump for my '73 Squareback is supposed to run 1-2
> sec. when the ignition switch is turned to the "on" position, then stop
> until the engine fires.  Mine did, but now runs all the time when the
> ignition is turned to "on."  Since the cutoff is a safety feature to prevent
> the pump from running when the engine quits, thereby preventing a gasoline
> catastophe, I need it to work properly. 

> My reading of various fuel injection manuals for the Bosch D-Jet suggests,
> but does not clearly state, that it is the fuel pump relay that controls
> this function.  Is this correct?  (makes sense to me, because this is an
> open loop system.)  If not, what does? 

Yes, it's a very good idea to keep this feature working correctly.

The fuel pump relay controls the pump, but the relay and its timing is 
controlled by the brain. Unless someone has changed the wiring for your relay 
or some of the FI wiring, I don't understand how you could get the failure you 
describe in a '73. I think failures in the brain should make the pump run ALL 
the time or none of the time, but I suppose it's possible that a failure in the 
brain timing circuit MIGHT give the symptoms you describe. I've never seen that 
happen.

If the pump actually runs continuously as long as the key is ON, then I THINK 
the problem has to be that either the relay has been rewired to be controlled 
by the key, or the relay has been bypassed so that the key feeds the pump 
directly.

Look at your pump relay. Pull the white plug off it and see if the pump still 
runs. If it does, move one of the 2 red wires to a different terminal. If you 
have an AT, there will be 3 red wires and finding the correct solution is 
slightly more difficult to describe.

In general: There are 3 tabs on the relay that are available after the white 
plug is installed. 2 of those are close together and are, in fact, the same 
connection. The red wire from the fuse box should go to the 3rd tab.

The other 1 (or 2 for AT) red wire(s) connect to the 2 tabs that are close 
together.

The red wire to the fuse box goes to a fuse that should serve no other load. 
That fuse should be hot all the time, not controlled by the key.

If pulling the white plug off the pump makes the pump not run at all, let me 
know and we'll think about other possibilities.

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




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