RE: 81-83 EFI system circuit analysis: Was (RE: IML: Question, of course!)

["Dick Benjamin" <dickb@xxxxxxxxx>]

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

 

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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. 

Ken

 

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

 

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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?