[T3] car died on way home

Bryon Garvin spinningrooves at gmail.com
Sat Apr 7 16:53:48 PDT 2012

Here's what happened:

Testing blue/white wire in plastic connector (back-probing method):  Got
12v with key turned, jumped to 14v when engine ran, back to 12v when engine

Testing white wire in plastic connector:  Got 12v when key turned, then

1st time: stayed at 12v while engine ran, when engine died, still showed 12v
2nd time: dropped to 5v while engine ran, when engine died, back up to 12v
3rd time: same as first

Hand on fuel relay under back seat confirms that it clicks off only when
the key is turned off.

Only other thing I'll say is that over time and doing test after test, the
engine stays running for less and less time each go-around.


 - Bryon, '71 Fastback FI/MT

On Fri, Apr 6, 2012 at 8:11 PM, Jim Adney <jadney at vwtype3.org> wrote:

> On 6 Apr 2012 at 19:38, Bryon Garvin wrote:
> > Here's the latest.  Got the volt meter out.  Turned key, got 14v out of
> the
> > FI relay under the dash.  Started the car.  Ran fine for 30-40 seconds,
> 14v
> > still coming out of relay... then voltage dropped to zero INSTANTLY.
>  There
> > was no gradual decline in output voltage.  Engine died.  When I did it
> > again, same thing happened and I felt the relay click off thru the probe
> I
> > was holding on the terminal.
> I agree that this sounds like the fuel pump relay may not be the
> problem. Here's what I would do next. There are 2 wires coming into
> that relay in a white plastic plug. You need to test those wires.
> Attach one of your voltmeter leads to ground and stick the other one
> in the backside of that connector (this is called "backprobing")
> making contact with each wire in turn, as the engine runs and fails.
> One wire comes from the main power relay. That should get 14 V as
> soon as the key is turned on and should stay there all the time the
> engine is running. That wire should stay high even after the engine
> stops.
> The other wire should go high when you turn the key on, but it should
> go low as soon as the engine starts to crank and stay low all the
> time the engine is running. It should stay low for about one second
> after the engine fails, as long as the key stays on.
> If you haven't done so already, check that the ground wire under the
> mounting screw for the main FI power relay is tight. You might also
> want to put a finger on that relay while doing your testing. That
> relay should only click off when you turn the key off.
> Make sure you know which relay under the back seat is the FI main
> power relay. It's the one with the dedicated red wire coming from the
> battery + terminal.
> Let us know what you find.
> --
> *******************************
> Jim Adney, jadney at vwtype3.org
> Madison, Wisconsin, USA
> *******************************
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