1975 California distributer wiring

[Dave WM]

Can someone confirm if the Green lead at the 2 term distributor block has a ground lead as well as the two green leads connected to it? My 1975 FSM is not clear on this, at least from what I could see in the actual wiring on the electrical chapter. The wiring diagram if I am reading it right does NOT show a grounding of the green lead. However on my car there is one, but it does not look factory. Furthermore if I disconnect it, the ign will not fire. IF I have the ign in the on position and start to remove it (causing an intermittent connect of the green wire to ground) the ign will fire (I can see the spark at the coil and here the injectors firing).

Some other testing I have done:

observe the ign thru a neon spark tester at the center lead of the dist cap, while cranking I get an inconsistent spark, If I remove the plugs from the car to lower compression (spins engine faster) the spark is consistent (continuous with no breaks). I checked the output of the dist pickup, I get about 200mv AC at normal crank speeds (plugs in). I compared this to my test engine setup that does not have the same inconsistent spark, it also output about 200mv AC. I did not break out the scope yet...

I have checked the voltages at the ign coil for correct dropping thru the ballast resistor with a test light and volt meter, full bright while cranking, less once running at the + side of the coil. check for voltages and grounds at the module itself.

All this is done since I notice that my test engine always starts nearly instantly while my car always seems to take several revolutions but always starts (not excessive just more, like 2-3 seconds vs a fraction of a second). I was thinking orig that maybe it was a fuel thing but I tested the spark and can see it cranking with no spark then after the 2-3 seconds there is a spark and instant start up.

the test engine shows spark instantly with no delay. The battery voltage is good, about 11v under starter load. I even swapped batteries, and both engines sound like plenty of crank speed, The test engine will start easy even when the battery is not it good shape.

Its not a big deal as it always starts but I just cant account for the difference in how quickly the sparking (and starting) takes place.

My next test will be to try a start with the remote starter while the key is in the on position, just to make sure I don't have any ign switch issues. its a new switch but its an easy thing to check. I did test light checks with the ign module under both "run" and "start"  positions, all past fine (full brightness with all leads that should be energized. I check the ground connection (black wire of ign module), it showed nearly zero resistance to the chassis ground. I also used the test light from hot lead to ground lead (just in case it was grounded but not a good ground). While its not much of a load I figured better than a meter. I tried a different module, same results, maybe even a longer crank time.

But I can not account for the looks like the extra ground lead on the green wire at the term block. That bothers me.

 

 

 

 

 

[Zed Head]

Seems like the grounding is through the ignition module, if it grounds.  It's a sine wave.  Maybe somebody "hacked" your system in the past to solve a problem.

Pretty sure 75 is the same as 76.  I had no extra grounds on my car and no extra grounds after I switched to a GM HEI module.  Might be worthwhile to try an HEI module. Worth having as an emergency spare, either way.

 

Edited December 26, 2019 by Zed Head

[Zed Head]

I just remembered that somebody had jumped the two terminals on my car, a Federal model.  I assume that one of the pickup coils had gone bad and they converted it, basically, to a single pickup coil distributor.

Or maybe they were going for multiple spark...

Edited December 26, 2019 by Zed Head

[Dave WM]

I wonder why the grounding of the green wire results in a discharge of the ign module? that is ign "on" engine not running, loosen ground at green wire, and it starts discharging as the circuit is broken.

I was contemplating disconnecting it while it was running to confirm the need for the ground being used in my setup. It def does not look factory as the terms look to be home made. Also noted heat shrink on the green and red leads near the block on the distributer side. As if someone replaced the end of the distributer cable. I did check the resistance both at the distributer lead and the ign module. 709 ohms. factory is about 720 so I think at least that looks correct. The distributer internals (reluctor/coil) look VERY clean no way its 45 yrs old so pretty sure something had been done.

I assume the HEI swap is pretty non invasive? so if I need to have as an backup I could do something easy.

Edited December 26, 2019 by Dave WM

[Zed Head]

You can hook up a GM HEI module without cutting any wires.  Completely reversible.

The ignition modules are designed to sense very small voltages, and the trigger is when it goes from negative to positive.  When you disconnect the wire you must be changing the potential across the two contact points.