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Fuel Pump Circuit

To: healeys@autox.team.net
Subject: Fuel Pump Circuit
From: Awgertoo@aol.com
Date: Tue, 4 Oct 2005 15:58:16 EDT
My wife's 3000 died over the weekend. On initial investigation it cranked 
fine and had a spark but empty fuel bowls. 

When I turned on the ignition I did not hear any ticking from the SU (her car 
came with one of the double-headed models) so I checked the circuit to 
it--test meter showed 12 volts. I disconnected the fuel supply line--The pump 
would 
give one gasp and emit a short burst of fuel when the ignition switch was 
turned on and no more.  Same thing when I turned the switch off-one click and 
that 
was it.  I removed the pump and checked it on the bench--same deal.

I went to the NAPA store and bought a FACET pump.  Checked it on the bench 
and it was fine.  I wired and plumbed it in and with the ignition switch turned 
on it clicked away and apparently pushed fuel to the engine.  However, 
whenever I started the engine the fuel pump would die--I could feel it stop 
clicking 
at the same time that the green "ignition warning" light would go off--and 
within a minute or so the engine would die.  I could also see that the fuel was 
not being pumped into the transparent inline fuel filter.

When I turn the ignition switch off and then back on the fuel pump energizes 
and keeps on ticking (less intensely once the system is pressurized) but as 
soon as I push the start button and the engine fires over the fuel pump 
switches 
off!

Here are some other observations:

1.  If I wire the pump directly to the battery there is no problem.  The pump 
will of course run with the engine off or on. I can see fuel being pumped 
into the transparent fuel filter.

2.  When I run a test light to the fuel pump power lead it lights when I turn 
on the ignition switch, blinks or dims a bit during starting (never really 
goes out), and stays lighted when the engine is running (this with the fuel 
pump 
wired directly to the battery as in #1 above.) 

3.  When I attach a test meter to the fuel pump power lead the voltage is 
around 12 with the ignition switch on and the engine off.  On startup the 
voltage 
goes up to 13+ (it's an analog meter and I'm testing on a 50 volt scale so I 
cannot get precise readings.) 

Best I can tell something is kicking the fuel pump off when the engine starts 
up but I am lost.  I have an alternator if that is important. The pump is 
wired for negative ground.

Any suggestions will be appreciated.
Best--Michael Oritt 




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