MemCals Needing RFD Tweeking Before Finding A Home......

[Ludis Langens]

Walter Sherwin wrote:
> 
> My
> original thought was to simply render RFD innocuous, and carry my cell phone
> and CAA card at all times, but I later resolved to explore the recal route
> in light of the DIY penchant that we all share.

A while ago, I think I found that one of the NETRES to RFD connections
could tell the RFD to shut up.  In other words, this one signal is used
to detect a missing MEMCAL.  When I bench run a P4 without NETRES's
installed, the RFD remains mute.

> REF,
> TPS, and CTS are fed into the RFDA and in turn the RFDA would seem to
> trigger the PMID to fire both injector channels in synchronous simultaneous
> fashion during RFD.

With a full MEMCAL installed, the RFD output runs continuously.  The
next chip in line is responsible for selecting between the RFD or the
digital logic.  BTW, the P4 RFD has just this one "output" signal.

> Q1 - Can these NETRES blocks be replaced by a creative breadboard circuit
> containing multiple cascade resistor devices?

Yes.

> Q2 - If so, in what arrangement would they get interconnected?   On the
> surface, there would appear to be more resistors than available pin pairs,
> so I am assuming that there is a certain degree of interconnectivity within
> each NETRES block.

I guess you haven't looked at my diagrams yet.  The resistors are very
much interconnected.  I've figured out the interconnections of the C3
1227170 & 1228746 CALPAKs (see the daughterboard pages).  From this it
is obvious that each pair of pins along a side of the NETRES can have a
resistor between them, and that each pin can have a resistor up to a
common bus bar.

> Q3 - Are there upper/lower "R" limits that a person should be aware of, so
> as to not let the smoke out?

Most of the resistors are arranged as voltage dividers.  I assume that
the only limit is to make sure that none of the dividers short out the
power supply.

> Q4 - This thing must have been calibrated by a mere "human" at one point in
> time working for the OE.  Anyone care to share experiences & thoughts and/or
> point toward alternate sources of understanding?

I suspect that understanding the late '70's Cadillac analog FI system
would be a good start.  GM seems to reuse their technology.  The RFD may
be based on the old Caddy circuit.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/

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