Re: [T3] running fuel pump w/o ignition on

["Jim Adney" <jadney@vwtype3.org>]

On 1 Apr 2010 at 18:39, J. Jonik wrote:

> Isn't this the same as just grounding the wire---ignition on---in the
> engine compartment...the fuel relay wire in that plastic in-line plug
> connector tucked in behind the manifold pipes on the No 3 and 4 side
> of the engine? 

The end result is the same: the fuel pump runs, but you're getting 
there by different means.

Shorting the red wires on the pump relay just sends power straight to 
the pump, without involving the relay. There's some advantage to this 
in that it takes a possibly defective relay out of the picture.

Shorting the wire in the engine compartment to ground actually 
energizes that relay, which generally works fine, but it depends on 
the relay being good.

> ÊThat is...can you get an accurate Fuel Pressure reading just by
> grounding that wire...which keeps the pump running while grounded?ÊÊ
> Or do you really have to crank the engine over for 8 seconds or so to
> get an accurate reading? 

Anything you do that keeps the pump running will allow you to do an 
accurate fuel pressure reading. You can do this by either means 
above, or by using the Bosch tester (which is equivalent to the 
second method above) or by just starting the engine and letting it 
run.

I think it would be hard to try to crank an engine that will not 
start while also trying to read a gauge. The other methods allow you 
to adjust the pressure while the pump runs, but I prefer to do this 
without running the engine or the starter, simply because then 
there's no moving parts, no spark, no rush, no exhaust gas, etc, etc. 

-- 
*******************************
Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA
*******************************


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