Perplexing Ignition Problem

pickman

pickman

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The 1973 sat for about 2 months occasionally charging the battery. During this time I exchanged transmissions. Yesterday took a ride and noticed the Tach is not working and it will not accelerate without stumbling badly. I checked the coil both primary 1.5 Oms and secondary 13 Mohms so I do not see the coil as the issue. I touched NOTHING else between drives. Put the old coil in and the Tach worked but its too weak to run the engine for just a few seconds. Put the new coil back and the car starts and idles OK.

I am as a loss as to what could have caused this change? What would cause the Tach to not work? I am using a ballast resistor and it really heats up.

It almost feels like its not advancing the ignition when accelerating have an old Mallory Unilite distributor with new cap.

Sure could use some leads!
 
Here's the Unilite instructions.

Wiring diagram...
Screen Shot 2021-03-13 at 12.06.51 PM.png


Make sure the wire to your tach is connected to the - terminal of the coil.
 
Try bypassing the ballast resistor and get full 12v to the coil. According to the diagram, the distributor is not in line with the resistor so no harm in doing so. Clean and tighten the spade connectors (male and female) of all wires attaching to the coil, one will also be the tach wire.
 
So, the transmission has a ground strap to the body. This is at the top of the transmission at the back of the engine bay. Did you replace the ground strap when you changed transmissions?

I not only have that ground strap, I have a ground strap from the body ground for the battery to the engine block, and another across one of the motor mounts.
 
Stevehose said:
Try bypassing the ballast resistor and get full 12v to the coil. According to the diagram, the distributor is not in line with the resistor so no harm in doing so. Clean and tighten the spade connectors (male and female) of all wires attaching to the coil, one will also be the tach wire.
Click to expand...

Might be risky. The instructions say...

"NOTE: The purpose of an ignition ballast resistor between the ignition switch (12V) and the ignition coil positive terminal is to restrict current flow through the ignition coil. Failure to use an ignition ballast resistor will eventually destroy the Ignition Module."
 
I hope you didn’t run the existing wire from the starter used on the old SR-71X if you installed a newer starter, it will fry the ballast resistor and glow cherry red. Just a thought.
 
The ballast resistor does run cherry red. BUT I have changed nothing. The ground strap was replaced from body to bellhousing. I can bypass the BR to see if this helps? Could something happened to the Distributor? Very strange occurrence as I have not touched the engine compartment during the trans swap.
 
Agreed, but briefly seeing if it resloves the problem won't hurt it. It theoretically gets full 12v when cranking

Dick Steinkamp said:
Might be risky. The instructions say...

"NOTE: The purpose of an ignition ballast resistor between the ignition switch (12V) and the ignition coil positive terminal is to restrict current flow through the ignition coil. Failure to use an ignition ballast resistor will eventually destroy the Ignition Module."
Click to expand...
 
I wonder if charging the battery while the main ground strap was disconnected did something to the ignition? The hard thing to swallow is I touched nothing in the engine compartment while rebuilding the trans. The ballast resistor glows bright red when running. Tach jumps around some.

Could this be a coil issue? Could it be the distributor? Not sure how to diagnose. It will idle only.
 
What is voltage at battery, ballast, and coil when idling? Did you bypass the ballast resistor to see if that solves the issue temporarily?
 
pickman said:
I wonder if charging the battery while the main ground strap was disconnected did something to the ignition? The hard thing to swallow is I touched nothing in the engine compartment while rebuilding the trans. The ballast resistor glows bright red when running. Tach jumps around some.

Could this be a coil issue? Could it be the distributor? Not sure how to diagnose. It will idle only.
Click to expand...

When you say "main ground strap", do you mean the connection from the negative terminal of the battery to the chassis? If so, and you you charged the battery by connecting the charger to the positive and negative battery terminals with the ground strap disconnected on the battery, this won't be our problem.
 
deQuincey said:
perplexing...ballast resistor glows !
Click to expand...

There should not be enough resistance to make anything glow like a toaster, that's a lot of heat. Something has or is presently creating a short circuit. Time for serious diagnosis with a voltmeter or shop who can & will remedy the problem. Remember, your car can kill you.
 
Removed the Ballast Resistor and the problem went away except it now sounds like the starter is not disengaged and spinning with the flywheel?

The ignition key barley turns and the engine turns over.

Something weird going on?
 
Removed the black and red wire from starter and it now runs normally. So you all talked me to this point now what is the solution with the ballast resistor? Certainly this solved all the issues.

Please advise.
 
Well, when you say you didn't change anything, there is a switch on the automatic transmission that prevents the car from starting unless the transmission is in park or neutral. You must have disconnected this switch to change transmissions, or at least detached it from the transmission you removed.

Did you use the same switch or did you get another switch with the new transmission?

And either way, are you sure the connector from that switch into the wiring harness is properly seated?
 
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