RE: [DML] Re: Fuel Pump Madness
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RE: [DML] Re: Fuel Pump Madness

Todd, The RPM relay has a 555 chip inside it that allows the pump to prime
up for about 2 sec every time the key is turned on and off. If this isn't
happening then I would replace the RPM relay after you have checked all the
connections. I have brand new ones for $34.95 with a 1 year warranty.
John Hervey


-----Original Message-----
From: dmcnews@xxxxxxxxxxxxxxx [mailto:dmcnews@xxxxxxxxxxxxxxx] On Behalf Of
Todd Nelson
Sent: Friday, July 07, 2006 4:07 PM
To: dmcnews@xxxxxxxxxxxxxxx
Subject: [DML] Re: Fuel Pump Madness

Responding to my own post....

After some more reading and research I have another question.  From what
I've read the RPM relay is not supposed to close unless it receives signals
from the impulse coil, so it doesn't run if the engine is off.  I see that
happening from the wire coming off of the impulse coil in the distributor
that then goes into the Ignition Control Unit.  Power is then transferred
from the ICU over the White/Slate wire to the RPM relay which in turn powers
the internal relay magnet and closes the relay, giving power to the pump and
CPR.  So...  Just from the book point of view I'd say that the pump not
turning on when the key is just placed in ON is normal, since the engine is
obviously not running.  So why then does the pump sometimes turn on and
"prime" for those couple seconds?  I've found that when is does "prime"
itself for those 2 seconds there is 0 Volts on the white/slate wire.  So how
in the world is the internal relay closing?  There must be some other source
of power that is causing that internal relay to close and that is what I
cannot determine.  The only source of power I can see that is switched with
the ignition switch is going to pin 15 on the relay, which comes from fuse
1.  Pin 15 then seems to go to the internal relay electromagnet coil, so it
would seem that 12V+ on this would close it, but alas it does not.

Does everyone else's fuel pump "prime" like this?  Every other car I've
driven (non DMC), new or old, I've always heard the fuel pump kick on for a
couple seconds before actually starting, so I have to think it is supposed
to do this all of the time.

I've tested my impulse coil and it checks out OK, about 600 Ohms.  Not that
it really matters since I'm only testing with the engine off.

Sorry for WAY over complicating this  :-)

Todd Nelson
1561, Vermont

  ----- Original Message ----- 
  From: Todd Nelson 
  To: dmcnews@xxxxxxxxxxxxxxx 
  Sent: Friday, July 07, 2006 11:50 AM
  Subject: Fuel Pump Madness


  I think I've done all I can do with this one, so I'm going to open it up
to you all.  After taking the car out of storage for the winter I noticed
that when I turned the key to the ON position the fuel pump didn't do its
regular 2-3 second prime then shut off.  Hmm I said and continued to flick
the key from ACC to ON. Finally the pump did its deal and the car started
fine.  I shrugged it off as some corroded contacts and went on my merry way,
only to find that the problem was back when I tried to restart again.  The
same "solution" of flicking the key seemed to work.  I have been told that
it may be dirty contacts on the ignition switch, but I don't think this is
it since the main relay for the ON position always works, and everything
else that is supposed to come on when in the ON position (dash lights,
engine electrical components, etc) all work fine.  I first suspected the RPM
relay, so I opened it up, cleaned the contacts on the relay and the same
problem continued.  After A LOT of testing I came to the conclusion that the
RPM relay was dead, I've heard they are prone to failure and I had an
original one, so it all added up.  $57 later at my local foreign parts shop
and my troubles continue!  But at least I have a spare RPM relay now.
During my testing I noticed that if I quickly (really quickly) plug and
unplug the #1 fuse a few times things will work, but if I slowly plug and
unplug the fuse things will not.  Same goes for the key, if I quickly flick
to the run position a few times the pump will run for those 2 seconds as it
should.  I've studied the wiring diagram of the car until migraines set in
and I can't seem to find anything else on this circuit to prevent the pump
from pumping.  It's not the inertia switch, I've bypassed that.  I was also
thinking possibly the "main fuel relay/LAMBDA relay" as it is on the
circuit.  But even with that unplugged the symptoms are the same, the pump
will still function (sometimes) with that relay removed, so that can't be
it.  I've cleaned all the contacts on the fuses, pump connections, relay
connections and ground points.  Once I get the pump going the car runs and
drives fine.

  Any thoughts?

  Todd Nelson
  1561, Vermont

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