Thanks for the clarification, Dick. Agree the ASDM design looks
like an afterthought. Reminds me of some of the quick fixes they made us
do to ship "prototypes" out to customers. But my quest here is
not purely academic, I have this machine running near perfectly, however, out
of the clear blue it will suddenly just die. Does not stumble, cough, or
anything, just dies at random times. All modules are the late production,
non-meltdown, all new filters, cleaned tank and pickup filter. Will not
restart until it gets stone cold again. Has fuel, spark, and turns over,
but no start. Same effect with bypassed ASDM. That's how I isolated
the common lead to the CCC. I am about to bite the bullet and gamble
on a "new" or "refurbished" CCC.
I’m copying the IML with this
discussion because I want to get all the thinking into the archives for the
future use of folks who are going to be keeping these cars going; I hope you
don’t object.
I hadn’t read your suggestion
carefully enough – I see now that you were proposing to disconnect the
wire at the ASDM and CCC, but leave the pump drive alone. I
can’t see a reason to do this, as the signal from pin 6 to the ASDM
cannot cause a noise problem once the car has started; the NAND gate consisting
of pins 12, 13 and 11 of the IC is in the “don’t care”
state. This is due to the fact that the starting signal (pin 13 of the
IC) has gone (low) once the key is released. The connection is
there only to initialize the first “flip/flop” and start the
in-tank pump for the purge cycle as soon as the circuit comes alive – it
is then ignored until the next cycle.
I can’t tell you what the pump drive
signal is used for inside the CCC, as we have no information on that item.
I assume it is used as a feedback signal for whatever analog circuit
generates the fuel demand signal – if that is the case, grounding it
would probably cause the pump drive to go to max (80PSI!) and stay there.
Fuel mileage would suffer, to put it mildly!
The bottom line is: try an experiment if
you wish, but my advice is - leave well enough alone.
The noise problems in the ASDM are due to a very poor design, namely the use of
“tied back NAND” type (unclocked rather than J-K) flip/flops, and
the absence of any solid grounding provision for the unit – both mistakes
invite severe noise problems, thus the service note about adding a ground wire
to the case.
Dick Benjamin
From: Ken W Stephenson
[mailto:kss37215@xxxxxxxx]
Sent: Sunday, July 24, 2005 9:23
PM
To: dickb@xxxxxxxxx
Subject: Re: 81-83 EFI system
circuit analysis: Was (RE: IML: Question, of course!)
Agree, but we would not disturb drive to Control pump, which is
internal to the hydraulic plate, just disconnect pin 6 and keep line to CCC,
pin 2, and ASDM, pin 4, low. Seems redundant the way it is.
Just a thought to eliminate another noise input to ASDM and CCC.
On Sun, 24 Jul 2005 21:37:36 -0700 "Dick Benjamin" <dickb@xxxxxxxxx> writes:
Pin 6 of the power module is the pump
drive signal output to the Control Fuel pump from the push/pull pair of power
driver transistors.
You must have been asking about some other
pin or connector – you won’t get far without pin 6!.
Dick
From:
mailing-list-owner@xxxxxxxxxxxxxxxx
[mailto:mailing-list-owner@xxxxxxxxxxxxxxxx] On
Behalf Of Dick Benjamin
Sent: Sunday, July 24, 2005 1:36
PM
To: 'Ken W Stephenson'
Cc: mailing-list@xxxxxxxxxxxxxxxx
Subject: 81-83 EFI system circuit
analysis: Was (RE: IML: Question, of course!)
-----Original Message-----
From: Ken W Stephenson
[mailto:kss37215@xxxxxxxx]
Sent: Sunday, July 24, 2005 11:42 AM
To: dickb@xxxxxxxxx
Subject: Question, of course!
The lead from pin 6 of the Power
Module to the CCC and ASDM. Obviously
controls shutdown. For what
reason? The ignition pulse train does the
same thing. Can I disconnect
it at the PM and ground the side to the CCC
and ASDM without losing
anything? Just trying to simplify this design.
Did anyone ever do a theory of operation
on the Power Module?
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