Computronics OUT, Disty IN, a Few Questions

[RRoller123]

So I am replacing my failed Computronics unit with the original distributor that came with the car ('80FI) and I have a few questions that are not apparent in the manual.

(Obviously I am NOT happy with this, the Compu was a lot of money, they fail at a high rate, and there is no service available).

At any rate:

The system looks like this:



I see how the control module goes, the vac hose, the spark plug and primary coil wire, the control module cable, 12VDC in from the IGN "ON/RUN" to "B", how the mounting plate goes, plenty of thermally conductive Gumpcukrus under the control module, "B" of cable (RED) passes through Control Module to "B" of coil, BLK to the other post, no problem, but where does the Condenser go?

First question: The thing I can't remember is where the Condenser hooks up? Can't find anything in the manual.

Second Question: The only external input to this system is the 12VDC to Coil "B" is that correct? Everything else I have shown in the picture. I can easily restore that if I am correct in this assumption.

It does passes all the electrical tests that are in the manual. Here are the various pages, they may be of help to others. THIS IS FOR '79 ON.

[SteinOnkel]

Ah, another gentleman burned by the computronix junk. I've been there, my friend.

Wire it up per this diagram:

https://lh3.googleusercontent.com/proxy ... 9mqAkA1cvb

The ground connection drawn for the screw hole just above terminal c is critical. You will not have a spark without it.

The condenser is only used with points ignition; this system makes it obsolete.

Yes, the coil plus and ignition module terminal b are the only things receiving inputs. 12v, switched. Make sure it's a full +12v and not a resistor wire that only supplies 9V.

[RRoller123]

Excellent, thanks! Now why the hell did my '80 FI Electronic ignition have the Condenser? I have an electronic ignition, no points. Hmm..... Makes sense that I don't see it in the manual.

I have to watch the tach wire too, forget to mention that, but I understand it. It hooks to the C pole opposite the B on the coil top.

I am irritated about the Compu. I really liked the simplicity and block mounting, high voltage, wider plug gap, ease of setup and timing, waste spark, etc, but if it isn't reliable, or cant be repaired, then that is really, really bad.

[RRoller123]

sorry, google error on that link.... Could you PM or type it out so I can copy paste. This forum doesn't allow direct links to outside sites, which makes a hell of a lot of sense.

Just to be clear, the Control unit gets its power from the 12VDC that comes in at B on the coil, and goes down to the control unit through the red wire I showed in my pic, no other external connection, literally just this one wire from the IGN switch to B on the coil? (plus of course the tach wire out) No other external connections? Except GND of course.

Maybe I should run a dedicated 12AWG or 10AWG wire from the IGN switch to Coil "B".... fuse it? Hmmmm...........

[spider2081]

The condenser is only used with points ignition; this system makes it obsolete.

I'm pretty sure the capacitor is a radio noise filter. It's ring terminal goes on the B terminal of the coil. The capacitor's wire points down this allows the clamp to just fit to be retained by the coils physical mounting strap with the stud. The other side of the coil retaining clamp is held in place by a small bolt.

[RRoller123]

Ah yes, it is all coming back now. Since I never listen to the radio..... But I guess I will put it back in anyway. Thanks to both of you for the help. This forum is invaluable.

Will be starting a new topic once my block goes back in shortly, driveline angle, pinion angle, matching, measuring etc. I find this of great interest, maybe others will too.

This shows the entire issue in a nutshell. Really interesting. Phasing not an issue, the prop shaft is welded.

https://www.youtube.com/watch?v=gmV4qwLfOMY

here is another one.

https://www.youtube.com/watch?v=jaaTyL099RA

[RRoller123]

One last question:

Does this massive heat sink need to be an electrical ground through it's mounting bolts, as well as a thermal ground? It doesn't seem like the coil case needs grounding, but I don't know.

[SteinOnkel]

Nothing fancy about this ignition, it's simply a GM HEI. Yes, you can ground through your heatsink. Aluminum is a great conductor. Tach simply goes to coil negative.

[RRoller123]

Thanks, I should have looked at my own posting, the drawings on page 55-20 clearly show the coil mounting strap through the heat sink going to ground.

[RRoller123]

OK, so I think I have it as to how to reverse the Computronix back to stock Electronic Distributor System:

Let's see if I have this right:

1) The RED from the IGN CONTROL MODULE goes to COIL "B".

2) The BLK from the IGN CONTROL MODULE goes to COIL "GND". (or the opposite of "B", it is not marked as anything on my coil, calling it "GND" here).

3.) The PINK from the IGN SWITCH "ON/RUN" goes to COIL "B".

4.) The BRN/WHT from the TACH goes to COIL "GND"

5.) The BRN/WHT from the ECU goes to COIL "GND"

6.) The CAPACITOR "+" RING TERM goes to COIL "B".

7.) The CAPACITOR GND STRAP goes to HEAT SINK and thus to GND.

8.) The HEAT SINK must ground to CHASSIS GND. (May run a dedicated wire for this, there's a lot of paint in the way..)

This puts (3) leads on COIL "B": The Control Module RED, the IGN SWITCH PINK, and the CAPACITOR RING TERM.

This also puts 3 leads on the COIL "GND": The BRN/WHT from the TACH, the BRN/WHT from the ECU, and the BLK from the
CONTROL MODULE.

Hope I have this right... An awful lot of simultaneous changes are going into this engine swap, that always makes me really nervous.

Pete

[SteinOnkel]

Here's Shia to give you the last bit of information:

https://www.youtube.com/watch?v=ZXsQAXx_ao0

[RRoller123]

Hahahah! Perfect! Also going to pull the heat sink and give it an acid bath to brighten it up. Phosphoric, I think. Going for it, lol.