DIY_EFI abilities and older engines

[J.W. Harris]

>To: dn <dn at dlogtech.cuc.ab.ca>
>From: jwharris at holli.com (J.W. Harris)
>Subject: Re: DIY_EFI abilities and older engines
>
>
>>and I think I've found a better unit than the stock HEI module, which fits 
into  
>>the stock HEI distributor (I think...).  It has a total of seven interface
>>terminals, including a spark reference output and input which should be easy
>>to interface to.  Problem is, none of the aftermarket parts catalogs that I
>>have have ANY technical info on the module itself (ie voltages, currents, 
etc.)
>
>As far as I know, there are 3 different types of HEI modules:
>
>The original 1975- ~80 "4 terminal" module.  Ground is thourgh the bolt 
holes and the other terminals are for: battery, coil-, and pickup +/-.  This 
is what I am currently using.
>
>The 5 terminal module. I think this one was used on trucks with ESC the 
extra pin is "delay". Not sure how it works.
>
>The 1981- end of distributor 7 terminal module.  This one has the terminals 
of the 4 term module and three others:  refrence: amplified pickup signal 
output.
>est: input signal from the ECM to fire the coil.  
>bypass: input used to select refrence if the est signal is bad or the 4 
wire connector to the ECM is dicconnected (To set timing).
>
>I think these are 5 volt signals but I'll have to check.  The levels are 
set to allow the ECM to detect an open, or short to battery/ground, then 
bypass mode will be used and the engine will be on base (~10deg.) timing 
Incidentally the direct fire systems have a similar interface.  
>
>I have the schematics for these modules, but of course I cant give them out.
>Looking at the signals with a scope on any '80's car so equipped would be 
educational and you would see what the voltage levels look like.
>>
>>Why dual?  One for the Wife?
>
>I needed 4 lines. Data is displayed like this:
>
>$aaaa: dd
>(bargraph here)
>
>a: address
>d: currnet value
>
>the s/w allows as many displays as wanted to be added using the same 
subrouintes. (until you fill the memory map)
>>
>>> The frist cut alogrithim will generate spark advance from RPM and MAP
>>> 
>>
>>Assuming you don't have access to a dynamometer, how would you generate a
>>spark timing table?  Also, would there be any advantage to using a MAF
>>sensor instead of MAP?  
>
>1.
>Using an advance timing light and the existing setup.
>
>Dinsconnect the vacuum advance.
>measure the timing advance at every 500 rpm or so.
>connect a vacuum pump and guage to the advacne.
>at idle (known advance) record the advance vs inches of Hg.
>enter these values into the spark advance table as a first cut.
>tweak as necessary (yes I know this could take a while.)
>
>2. 
>I don't know if anyone does it this way but I don't intend to use the 
complicated (expensive) and annoying to plumb MAF sensor.  Mabye there would 
be some value in experimenting with it.
>
>
>JW
>
----------------------------------------------------------------------------
J.W. Harris                                          Delco Electronics Corp.
Project Engineer                                     One Corporate Center
Powertrain Electronics                               M.S. CT40C
                                                     Kokomo, IN 46904-9005
jwharris at kocrsv01.delcoelect.com

Of course, all responses are my own and should not be mistaken for those of
Delco Electronics or General Motors.