[DML] Re: Fuel pressure & RPM Relay

["endotex23" <endotex23@xxxxxxxxx>]

--- In dmcnews@xxxxxxxxxxxxxxx, "Matt Spittle" <supermatty@xxxx>
wrote:
 > I studied the diagram to answer my own question, and I wasn't able 
> to; not even with a background in electrical engineering.<

Matt, first off I apologize if I offended you. I was both making a 
point about learning things in general and also making a few
assumptions in your particular case. The assumption I was making is
you were aware of the RPM relay's function. As you pointed out it's
stated in the manual and the diagram shows the relay as having an
input from the ignition module. To anyone trained in circuit analysis
that should have jumed right out. Plus the archives are full of
references to this because of it's associated effect on the fuel pump
circuit and the relay is also used in many other vehicles for the same
purpose. I assumed it was common knowledge among anyone who has owned
the car for a period of time and among anyone who frequents the DML.
Since you're not a new owner (and one with a background in electrical
engineering) I also assumed you had already developed a basic working
knowledge of the car's electrical system and were aware of this
detail. I shouldn't have made any of those assumptions. My bad.

It's obvious from the diagram the frequency valve is sunk, not
sourced, for control. There is only one power input on the Lambda
controller so it should be intuitive the valve will not operate unless
power is supplied to the controller via the RPM relay. Since the
controller has but a single output sunked to the frequency valve (and
since the service manual in many places states what this output does)
a schematic of the controller should not be required to fathom it's
basic operation. It's sole purpose is to control the frequency valve
at a variable duty cycle in response to a hot O2 sensor (closed loop)
or at a fix duty cycle during open loop and during a contact closure
of either the WOT or coolant switch. It must be powered to do this and
as you say, the key to understanding when the controller (and hence
the frequency valve) is active lies in understanding the RPM relay. 

I should not have made the assumption you were aware of the relay's
purpose, as well known as it seems to be. I also assumed people would
do a quick search of the archives or service manual prior to asking.
In some ways it further validates my opinion about learning things
versus handholding but again, my apologies. As David points out,
perhaps lower expectations on my part are in order.

Greg








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