AW: [DML] Re: Fuel pressure & RPM Relay

["Elvis Nocita" <elvisnocita@xxxxxx>]

[MODERATOR NOTE:  Let's be nice to each other here.  Please keep the discussion civilized, not accusatory.  -moderator Mike Substelny]

David,
you do help people a lot with your answers and the experience you have.
I am sure I profitted from it in the past, too.

This fact, that people trust you blind makes it even worse that
you don't even use the schematic to take a quick look on it.

How many people out there now think that their idle speed motor
should stop making that buzzing sound after a few seconds ?
They are totally mislead because it is supposed to buzz as long as
the key is inserted and turned to the position where all the bulbs 
in the dash are on. The green wire to the idle ECU is fed by the AUX
relay and fuse #1 - it's not even connected to the RPM relay !

On another note - I played with many RPM relays so far and there are 
different ones out there. While it is the regular case, that the pump 
is not activated when you turn the key, there are some out there which
do that (while I think is a good idea). Some may do it because of a 
spike that triggers it, but I think (can't prove it because I didn't
redraw the schematic of all of them) most of them do it always because
they are supposed to do it and built like that. At least I know that the 
Volvo or Renault replacement part does it for sure.

You are absolutely right when you say that is it extra hard to find a 
problem by remote. It is very often impossible without seeing the car
to diagnose things like you said. This makes it even more important
that then at least one who trys to help doesn't give wrong advices
because he doesn't even take a quick look at the schematic.

Please go on with your good work but verify it first, please.

Elvis



Actuallly it is not quite that simple. Yes, all these engine systems
are controlled by the RPM relay. It is *supposed* to prevent these
systems from continuiously operating if the ignition key is on and the
motor is not running. In practice I have seen cars where it does not
quite work this way. For instance when first powering up the RPM relay
is supposed to pulse so the fuel pump can run enough to provide some
fuel pressure to get the motor started. In many cases it stays powered
a lot longer than a "pulse". BTW the idle motor system is also
controled by the RPM relay so it should go quiet too along with the
frequency valve. Reference D:05:03. I think one of the points to be
made here is when working on old cars (including Deloreans) we
(mechanics and technicians) start to assume that many things are
hooked up and working the way they are supposed to except for that one
problem that the owner/driver has identified. We have to start
somewhere and assume that SOMETHING is correct or we might never get
anything done. The problem with that is that from past experience you
really can't trust everything, I have seen things like the wrong
relays in the wrong places, wrong fuses, things unplugged, jury-rigged
wiring, (especilly in the fuel pump circuit and cooling circuit). When
giving advice by remote control you are in an even worse position.
>From my many years of experience I could spot something that would be
obvious to me but someone else may never see but I can't see it
because I am not there. There was one car that wouldn't start and run
properly. It finally was mentioned that he had the hot-start relay. As
soon as he pulled it the car ran fine. Now, in a quick visual
inspection I may have spotted that and fixed it in a minute. Instead
we guessed at many things and sent the poor guy down a lot of blind
alleys. We all do the best we can. I am not in this for money but to
only help get as many Deloreans running as good as possible. I am not
perfect but I do the best I can. I appreciate that many people read my
posts and think I am helping them. Anyway the short answer is that the
frequency valve will buzz if the motor is not running but after a
short while (if the RPM relay is working correctly) it should stop
buzzing and the idle motor should be quiet. Same goes for the fuel
pump. The time does vary a lot. Another quick point to be made. The
origional RPM relay has a failure rate. It isn't high but it is
significant. Every owner should be aware of this and know how to
jumper it so the car can be driven home. It is not safe to drive
continuosly with a jumpered RPM relay but it is OK to do in an
emergency for a limited time. You must be very aware that the key is
OFF if the motor is not running. In my defense I do not research every
question and sometimes I do give answers "off the top of my head".
David Teitelbaum
vin 10757 







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