GM HEI circa 1985 info needed

[Jason Weir]

Stowe, Ted-SEA wrote:

> hi, I am working on building a mutant Lucas/gm distributor for my mg
> tbi
> project.
>
> I have a '85 tbi system from a sunbird, which uses a HEI distributor.
>
> I have the matching GM ignition module which would of gone into that
> set-up.
> and I have a Lucas distributor which uses a hall effect sensor, which
> fits
> into my block.
>
> my problem is that the Lucas sensor has a 3 wires coming out of it,
> whereas
> the gm hall effect sensor uses 2. the gm system looks pretty simple
> actually. so I am trying to figure out why the pommys used 3 wires.
> one
> might be a ground ? or center tap ??
>
> I suppose I could hook it up on a bench with a coil and work on
> combinations
> until I zap myself.
> but I don't want to blow the module nor the sensor in the distributor.
> and
> without the ECU attached I don't know if that would work anyway ??
>
> also I get the idea that the ECU controlled all of the timing, so I
> would
> just take out the mechanical advance in the distributor and lock down
> the
> top plate ??
>
> and would this module fire off an external coil ok, as opposed to the
> built
> in GM coil ?
>
> and I see that the gm module has a heat sink area, something I have to
> work
> on, how much heat did that module put out ?
>
> thanks for your always excellent advice.
>
> Ted Stowe

Ted,    I ran into all of the problems that you mentioned above when I
did my Jeep TBI conversion.  My fixes are as follows

1. My pickup had three wires, I used a DVOM to find the one that went to
ground, it actually was tied to ground inside the distributor and then I
just hooked up the other 2 in the configuration that gave me the most
advance.... I am still playing with this to get correct pickup and
rotor/cap alignment (see #2)

2.  I removed the vacuum advance and then removed the springs and
weights of the centrifugal advance I used lockwire to disable the
centrifugal movement... Then I used epoxy to hold the top plate from
moving... I got it a little bit retarded so when the pickup fires the
rotor is not positioned exactly how I want it, but I have not had the
time to get around to fixing it...

3.  I used the HEI module with no heatsink and it would cut out
periodically so I got a couple of CPU heatsinks with fans.. It just
happens that CPU fans are 12V so I wired them up to switched power so
they run when the ignition is on...


--
Jason Weir
88 Wrangler - 258 Chevy TBI
Fayetteville, North Carolina
http://home.att.net/~jweir  --- Jeep Home Page
mailto:jweir at att.net