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76 Tac Drop, Stall, Trouble Starting


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Really need help on this issue that has plagued an otherwise great and reliable car.

The car will be driving fine and the tac will drop to 0, the engine stalls, then usually there is difficulty in restarting the engine.  Because the tac dies suddenly I am leaning toward it being an electrical issue.  I would have replaced the ignition switch but that seems hard to find.  Need help about that. 

 

Battery recently tested 

123 Bluetooth Distributor

Have replaced the coil multiple times (Bosch blue coil)

Ballast resistor wire removed 

Distributor cap, rotor, wires, and spark plugs about 1 year old.
New Pieburg fuel pump (twice one failed after 4 months)

Webber 3838 with electric choke

New fuel line

Tank pickup is missing screen since screen plastic retaining clips broke.  Where can I get a new retaining clip?

Tank is clean

Metal cylinder fuel filter

Carb recently cleaned

Air filter cleaned 

Idle jet cleaned multiple times

Uploading video of coil voltages

 

Really hoping to resolve this issue once and for all. It’s a bad situation to stall in traffic. 
 

Thanks

 

 

9D798D18-98D8-4F6B-BE23-0B85A1DEC503.jpeg

A85B4D64-37A6-4D02-B603-C9955BBEDC1E.jpeg

Edited by Carson
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Thanks SOMarty.  As I understand it there are 4 wires to the coil. 
One to 123 Distributor Negative

One to 123 Distributor Positive 

One to Tachometer 

One to fuse box


The tachometer wire and fuse box wire are the only two wires that aren’t new.  I use heat shrink connectors and shrink tubing over that so if I have a short, it’s probably the old wiring.  

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wiring-negtuneplus.png

 

 

9 minutes ago, Carson said:

One to Tachometer 

One to fuse box

I have a 123 distributor and don't remember a tach or fuse box connection.

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Posted (edited)

In my case my battery is in the trunk. So my blue wire is grounded to the chassis and the red wire going off the coil in the pic goes to the fuse box and then on to the ignition switch.

 

One thing that does worry me is that all this wiring is above the exhaust header and that heat shield is poor.  Is there a better solution for that?

Edited by Carson
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With this symptom, its definitely the low tension circuit of the coil which is failing... if other electricals continue to work (Radio, Headlamps etc) then look closely at the ignition itself... The ground and power of the 123 unit, the condition of the coil...and if that is all good then look at the black wire that runs to the tach.

If all the electrics drop out then its just a general battery connection issue.

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Posted (edited)

I believe it’s just the tac and ignition that cuts out.  Lights and radio stay on.

Maybe I should disconnect the tac wire and drive.  I feel like the 123 wiring is good.

Maybe I need to run a new wire to the fusebox if it’s not the tac wire. 
I’ve replaced the coil several times.  It’s hard to imagine they keep going bad. 

Edited by Carson
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The engine itself needs a solid path to ground. The standard path is a braided flat wire with two sections that connect the engine block and the chassis to the battery negative.  If you relocated the battery to the trunk, did you replace the block to chassis connection?  I didn’t when I first relocated my battery to the trunk, but didn’t realize the importance because for the most part things still worked - somehow electrons were getting enough path to ground for it to start and run.  However I soon started to see gremlins - erratic temp gauge, erratic tach, occasional hiccups / misses.  I replaced the block ground and all the problems went away.

Edited by Solarphil
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Check the connectors on the black wires. The one on the distributor is especially prone to failing internally (looks good on the outside, but wires are broken inside). This will display the symptoms you describe...tach drop, intermittent miss, hard restart.

 

Ignition Circuit.jpg

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From the look of your factory wiring, in the older blue sheath, you may still have the resistor section in it, these can break down over time and with a blue coil anyway it's not needed. The resistor looks like a piece of speaker wire and it's with in the last 4-6" of the coil connector.

Edited by Son of Marty
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