[DML] Re: Fuel Pump Madness
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[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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