DIY_EFI abilities and older engines
J.W. Harris
jwharris at holli.com
Wed Dec 6 04:01:10 GMT 1995
>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.
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